[rust-renderer] Standalone preprocessing (#36718)

Signed-off-by: Sage Ahrac <sagiahrak@gmail.com>
Co-authored-by: Shangming Cai <csmthu@gmail.com>
Co-authored-by: Liangsheng Yin <hnyls2002@gmail.com>
Co-authored-by: Rain Jiang <96632942+rainj-me@users.noreply.github.com>

docker/renderer.Dockerfile

@@ -0,0 +1,89 @@
+# syntax=docker/dockerfile:1
+
+# Keep the compiler aligned with rust/rust-toolchain.toml. Pin image indexes
+# rather than individual architecture manifests so both platforms use this file.
+FROM rust:1.92.0-slim-bookworm@sha256:f1f73538ebe623fd3673a35aff3df358ae1084c64c55646516e5b17b321b6c9b AS build
+
+ARG TARGETARCH
+ARG CARGO_BUILD_JOBS=4
+ENV RUSTUP_TOOLCHAIN=1.92.0 \
+    CARGO_BUILD_JOBS=${CARGO_BUILD_JOBS} \
+    PCRE2_SYS_STATIC=1
+
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends build-essential pkg-config \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /build
+COPY rust/Cargo.toml rust/Cargo.lock rust/rust-toolchain.toml rust/
+# Cargo loads every workspace member even when building only the renderer.
+COPY rust/sglang-grpc/Cargo.toml rust/sglang-grpc/
+COPY rust/sglang-grpc/src/ rust/sglang-grpc/src/
+COPY rust/sglang-mm/Cargo.toml rust/sglang-mm/
+COPY rust/sglang-mm/src/ rust/sglang-mm/src/
+COPY rust/sglang-server/Cargo.toml rust/sglang-server/
+COPY rust/sglang-server/src/ rust/sglang-server/src/
+COPY rust/sglang-renderer/Cargo.toml rust/sglang-renderer/
+COPY rust/sglang-renderer/src/ rust/sglang-renderer/src/
+
+# Avoid rustup downloading development components from rust-toolchain.toml,
+# but fail if the image's compiler and the workspace toolchain drift apart.
+RUN channel=$(sed -n 's/^channel = "\([^"]*\)"/\1/p' rust/rust-toolchain.toml) \
+    && case "${RUSTUP_TOOLCHAIN}" in "$channel"|"$channel".*) ;; *) exit 1 ;; esac
+
+RUN --mount=type=cache,id=renderer-registry-${TARGETARCH},target=/usr/local/cargo/registry,sharing=locked \
+    --mount=type=cache,id=renderer-git-${TARGETARCH},target=/usr/local/cargo/git,sharing=locked \
+    --mount=type=cache,id=renderer-target-${TARGETARCH},target=/build/rust/target,sharing=locked \
+    cargo build --manifest-path rust/Cargo.toml -p sglang-renderer \
+        --bin sglang-renderer --release --features http --locked \
+    && install -D rust/target/release/sglang-renderer /out/sglang-renderer
+
+# Run the existing unit suite in the same Linux toolchain used for the image.
+# This sibling stage is selected by CI and is not a dependency of the runtime.
+FROM build AS test
+COPY rust/sglang-renderer/tests/ rust/sglang-renderer/tests/
+COPY experimental/sgl-router/tests/fixtures/tiny_tokenizer.json experimental/sgl-router/tests/fixtures/tiny_tokenizer.json
+RUN --mount=type=cache,id=renderer-registry-${TARGETARCH},target=/usr/local/cargo/registry,sharing=locked \
+    --mount=type=cache,id=renderer-git-${TARGETARCH},target=/usr/local/cargo/git,sharing=locked \
+    --mount=type=cache,id=renderer-target-${TARGETARCH},target=/build/rust/target,sharing=locked \
+    cargo test --manifest-path rust/Cargo.toml -p sglang-renderer --features http --locked
+
+FROM debian:bookworm-slim@sha256:88200866dfff7ea7f5cbcb6ec7c8a701889efe6fe859fe64d6990e4b07ea4171 AS runtime
+
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends ca-certificates libgcc-s1 \
+    && rm -rf /var/lib/apt/lists/* \
+    && groupadd --gid 65532 sglang \
+    && useradd --uid 65532 --gid 65532 --no-log-init --create-home \
+        --home-dir /home/sglang --shell /usr/sbin/nologin sglang \
+    && mkdir -p /home/sglang/.cache/huggingface \
+    && chown -R 65532:65532 /home/sglang
+
+COPY --from=build /out/sglang-renderer /usr/local/bin/sglang-renderer
+COPY LICENSE /usr/share/licenses/sglang-renderer/LICENSE
+
+# Metadata changes must not invalidate compilation.
+ARG SGLANG_BUILD_COMMIT=unknown
+ARG SGLANG_BUILD_URL=
+ARG SGLANG_IMAGE_TAG=local/sglang-renderer:dev
+ENV HOME=/home/sglang \
+    HF_HOME=/home/sglang/.cache/huggingface \
+    SGLANG_BUILD_COMMIT=${SGLANG_BUILD_COMMIT} \
+    SGLANG_BUILD_URL=${SGLANG_BUILD_URL} \
+    SGLANG_IMAGE_TAG=${SGLANG_IMAGE_TAG}
+LABEL org.opencontainers.image.source="https://github.com/sgl-project/sglang" \
+      org.opencontainers.image.licenses="Apache-2.0" \
+      org.opencontainers.image.revision="${SGLANG_BUILD_COMMIT}" \
+      org.opencontainers.image.version="${SGLANG_IMAGE_TAG}" \
+      org.opencontainers.image.url="${SGLANG_BUILD_URL}" \
+      ai.sglang.build.commit="${SGLANG_BUILD_COMMIT}" \
+      ai.sglang.build.url="${SGLANG_BUILD_URL}" \
+      ai.sglang.image.tag="${SGLANG_IMAGE_TAG}"
+
+USER 65532:65532
+WORKDIR /home/sglang
+EXPOSE 30000
+# The renderer's existing graceful shutdown handler listens for Ctrl-C.
+STOPSIGNAL SIGINT
+ENTRYPOINT ["/usr/local/bin/sglang-renderer"]
+CMD ["--help"]

rust/Cargo.lock

@@ -703,6 +703,16 @@ version = "0.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3d52eff69cd5e647efe296129160853a42795992097e8af39800e1060caeea9b"
 
+[[package]]
+name = "core-foundation"
+version = "0.9.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "91e195e091a93c46f7102ec7818a2aa394e1e1771c3ab4825963fa03e45afb8f"
+dependencies = [
+ "core-foundation-sys",
+ "libc",
+]
+
 [[package]]
 name = "core-foundation-sys"
 version = "0.8.7"
@@ -1076,6 +1086,15 @@ version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "34aa73646ffb006b8f5147f3dc182bd4bcb190227ce861fc4a4844bf8e3cb2c0"
 
+[[package]]
+name = "encoding_rs"
+version = "0.8.35"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "75030f3c4f45dafd7586dd6780965a8c7e8e285a5ecb86713e63a79c5b2766f3"
+dependencies = [
+ "cfg-if",
+]
+
 [[package]]
 name = "equator"
 version = "0.4.2"
@@ -1510,15 +1529,18 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "629d8f3bbeda9d148036d6b0de0a3ab947abd08ce90626327fc3547a49d59d97"
 dependencies = [
  "dirs",
+ "futures",
  "http",
  "indicatif",
  "libc",
  "log",
+ "num_cpus",
  "rand 0.9.5",
  "reqwest",
  "serde",
  "serde_json",
  "thiserror",
+ "tokio",
  "ureq",
  "windows-sys 0.60.2",
 ]
@@ -1637,9 +1659,11 @@ dependencies = [
  "percent-encoding",
  "pin-project-lite",
  "socket2 0.5.10",
+ "system-configuration",
  "tokio",
  "tower-service",
  "tracing",
+ "windows-registry",
 ]
 
 [[package]]
@@ -3293,9 +3317,11 @@ checksum = "eddd3ca559203180a307f12d114c268abf583f59b03cb906fd0b3ff8646c1147"
 dependencies = [
  "base64 0.22.1",
  "bytes",
+ "encoding_rs",
  "futures-channel",
  "futures-core",
  "futures-util",
+ "h2",
  "http",
  "http-body",
  "http-body-util",
@@ -3304,6 +3330,7 @@ dependencies = [
  "hyper-util",
  "js-sys",
  "log",
+ "mime",
  "mime_guess",
  "percent-encoding",
  "pin-project-lite",
@@ -3696,6 +3723,35 @@ dependencies = [
  "ureq",
 ]
 
+[[package]]
+name = "sglang-renderer"
+version = "0.1.0"
+dependencies = [
+ "async-stream",
+ "axum 0.8.9",
+ "clap",
+ "dynamo-parsers",
+ "dynamo-protocols",
+ "dynamo-renderer",
+ "dynamo-tokenizers",
+ "flume",
+ "futures",
+ "hf-hub",
+ "minijinja",
+ "regex-syntax",
+ "reqwest",
+ "rmp-serde",
+ "rmpv",
+ "serde",
+ "serde_json",
+ "thiserror",
+ "tokio",
+ "tower 0.5.3",
+ "tracing",
+ "tracing-subscriber",
+ "uuid",
+]
+
 [[package]]
 name = "sglang-server"
 version = "0.1.0"
@@ -3959,6 +4015,27 @@ dependencies = [
  "syn 2.0.119",
 ]
 
+[[package]]
+name = "system-configuration"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a13f3d0daba03132c0aa9767f98351b3488edc2c100cda2d2ec2b04f3d8d3c8b"
+dependencies = [
+ "bitflags",
+ "core-foundation",
+ "system-configuration-sys",
+]
+
+[[package]]
+name = "system-configuration-sys"
+version = "0.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8e1d1b10ced5ca923a1fcb8d03e96b8d3268065d724548c0211415ff6ac6bac4"
+dependencies = [
+ "core-foundation-sys",
+ "libc",
+]
+
 [[package]]
 name = "tagptr"
 version = "0.2.0"
@@ -4752,6 +4829,17 @@ version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
 
+[[package]]
+name = "windows-registry"
+version = "0.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "02752bf7fbdcce7f2a27a742f798510f3e5ad88dbe84871e5168e2120c3d5720"
+dependencies = [
+ "windows-link",
+ "windows-result",
+ "windows-strings",
+]
+
 [[package]]
 name = "windows-result"
 version = "0.4.1"

rust/Cargo.toml

@@ -3,6 +3,7 @@ resolver = "3"
 members = [
     "sglang-grpc",
     "sglang-mm",
+    "sglang-renderer",
     "sglang-server"
 ]
 exclude = ["sglang-radix-tree"]

rust/sglang-renderer/Cargo.toml

@@ -0,0 +1,54 @@
+[package]
+name = "sglang-renderer"
+description = "Reusable SGLang request preprocessing with an optional OpenAI frontend"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[features]
+default = []
+http = [
+    "dep:axum",
+    "dep:clap",
+    "dep:reqwest",
+    "dep:tokio",
+    "dep:tracing-subscriber",
+    "hf-hub/rustls-tls",
+    "hf-hub/tokio",
+]
+
+[[bin]]
+name = "sglang-renderer"
+path = "src/main.rs"
+required-features = ["http"]
+
+[dependencies]
+async-stream = { workspace = true }
+flume = "0.12.0"
+futures = { workspace = true }
+serde = { workspace = true }
+serde_json = { workspace = true }
+thiserror = { workspace = true }
+tracing = { workspace = true }
+tokio = { workspace = true, optional = true }
+uuid = { workspace = true }
+
+axum = { version = "0.8.9", features = ["json"], optional = true }
+clap = { version = "4", features = ["derive"], optional = true }
+reqwest = { version = "0.12", default-features = false, features = ["json", "rustls-tls", "stream"], optional = true }
+tracing-subscriber = { workspace = true, optional = true }
+dynamo-parsers = "7.0.1"
+dynamo-protocols = "5.1.0"
+dynamo-renderer = "5.0.0"
+hf-hub = { version = "0.4", default-features = false }
+minijinja = { version = "2.24.0", features = ["unstable_machinery"] }
+regex-syntax = "=0.8.11"
+
+# Keep this paired with the server until Dynamo exposes a smaller tokenizer API.
+dynamo-tokenizers = "1.7.0"
+
+[dev-dependencies]
+tokio = { workspace = true }
+rmp-serde = "1"
+rmpv = { version = "1", features = ["with-serde"] }
+tower = { version = "0.5", features = ["util"] }

rust/sglang-renderer/README.md

@@ -0,0 +1,104 @@
+# SGLang renderer
+
+The renderer runs as a separate service. It owns text preprocessing, token decoding,
+and OpenAI chat/completion responses. It submits token IDs through the native
+Rust server's existing `/generate` endpoint.
+
+The renderer targets the existing `/generate` contract on SGLang main and must
+work with an unmodified Rust server. It accepts both cumulative and incremental
+streaming responses, using the engine's configured format. Additional generate
+request fields or server behavior changes are deferred to separate PRs.
+
+## Build and run
+
+From the repository root, build the standalone renderer. Rendering and
+tokenization work without an engine; generation requires a running SGLang engine.
+
+```sh
+cargo build --manifest-path rust/Cargo.toml -p sglang-renderer --release --features http --locked
+```
+
+Start the engine in one terminal.
+
+```sh
+SGLANG_RUST_SERVER=1 python -m sglang.launch_server \
+  --model-path meta-llama/Llama-3.1-8B-Instruct \
+  --host 127.0.0.1 --port 30001 --skip-server-warmup
+```
+
+Keep engine tokenization enabled for stop conditions and minimum-token handling.
+
+Start the renderer in another terminal. Match the engine's model revision,
+tokenizer, context limit, and sampling defaults. Set tool and reasoning parsers
+on the renderer when needed.
+
+```sh
+rust/target/release/sglang-renderer meta-llama/Llama-3.1-8B-Instruct \
+  --engine-url http://127.0.0.1:30001 \
+  --host 127.0.0.1 --port 30000 \
+  --sampling-defaults openai --proxy-unhandled-routes
+```
+
+Send OpenAI requests to port 30000. With `--proxy-unhandled-routes`, routes such as
+`/v1/models` and engine health checks are forwarded to the engine. The renderer's
+own `/_sglang_renderer/ready` endpoint returns HTTP 204 with
+`x-sglang-renderer: ready`; engine readiness is checked separately.
+
+For preprocessing without an engine, omit `--engine-url`. This mode serves render
+and tokenization endpoints without inference.
+
+```sh
+rust/target/release/sglang-renderer meta-llama/Llama-3.1-8B-Instruct \
+  --host 127.0.0.1 --port 30000 --sampling-defaults openai
+```
+
+The CLI defaults to sampling parameters from the model's generation config.
+`--sampling-defaults openai` matches SGLang's OpenAI API defaults. Use
+`--help` for template, parser, and limit options. A custom Cargo target directory
+or compilation target changes the executable path shown above.
+
+## Tool-call parser support
+
+`--tool-call-parser` uses Dynamo's parsers. See
+[Dynamo's supported tool-call parsers](https://docs.nvidia.com/dynamo/dev/parsing/tool-call-parsing#supported-tool-call-parsers)
+for parser names and model formats. These SGLang names need special attention:
+
+| SGLang name | Renderer support |
+| --- | --- |
+| `llama3` | Accepted alias for `llama3_json` |
+| `qwen` | Accepted alias for `qwen25` |
+| `glm`, `glm45` | Accepted aliases for `glm47` |
+| `deepseekv3` | Use `deepseek_v3` |
+| `gpt-oss` | Use `harmony` |
+| `step3` | Unsupported |
+
+Reasoning parsers are configured separately with `--reasoning-parser`.
+
+## Docker image
+
+Build the CPU-only renderer image from the repository root (`linux/amd64` or
+`linux/arm64`).
+
+```sh
+docker buildx build --load -f docker/renderer.Dockerfile \
+  -t local/sglang-renderer:dev .
+```
+
+Run preprocessing without an engine.
+
+```sh
+docker run --rm -p 30000:30000 \
+  -v renderer-cache:/home/sglang/.cache/huggingface \
+  -e HF_TOKEN \
+  local/sglang-renderer:dev meta-llama/Llama-3.1-8B-Instruct \
+  --host 0.0.0.0 --sampling-defaults openai
+```
+
+For inference, add `--engine-url` with a URL reachable from the container.
+
+## Current scope
+
+OpenAI serving supports text chat and completions. Multimodal OpenAI inputs,
+`/responses`, and `/messages` are deferred. Automatic engine launch and packaged
+renderer installation are also deferred; manage both processes explicitly.
+The renderer does not implement API-key authentication or TLS.

rust/sglang-renderer/src/config.rs

@@ -0,0 +1,37 @@
+//! Immutable configuration required during request rendering.
+
+use serde::{Deserialize, Serialize};
+
+#[derive(Clone, Debug, Default, PartialEq, Serialize, Deserialize)]
+pub struct SamplingDefaults {
+    pub temperature: Option<f64>,
+    pub top_p: Option<f64>,
+    pub top_k: Option<i64>,
+    pub min_p: Option<f64>,
+    pub repetition_penalty: Option<f64>,
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct RendererLimits {
+    pub vocab_size: u64,
+    pub context_len: u64,
+    pub num_reserved_tokens: u64,
+    pub allow_auto_truncate: bool,
+    pub enable_return_hidden_states: bool,
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct RendererConfig {
+    pub served_model_name: String,
+    pub tokenizer_path: String,
+    pub revision: Option<String>,
+    pub model_path: String,
+    pub chat_template: Option<String>,
+    pub tool_call_parser: Option<String>,
+    pub reasoning_parser: Option<String>,
+    #[serde(default)]
+    pub default_chat_template_kwargs: std::collections::HashMap<String, serde_json::Value>,
+    pub stream_response_default_include_usage: bool,
+    pub default_sampling_params: SamplingDefaults,
+    pub limits: RendererLimits,
+}

rust/sglang-renderer/src/engine/decode.rs

@@ -0,0 +1,427 @@
+//! Prompt and generated-token decoding, including local text stops.
+
+use super::{internal, invalid};
+use crate::{
+    GenerateRequest, GenerationOutput, GenerationOutputExtras, ResponseError, TokenIds,
+    TokenLogprob,
+};
+
+use super::{GenerationFinishReason, GenerationStream, MatchedStop, TokenStream};
+use futures::StreamExt;
+
+/// Shared tokenizer handle for prompt and generated-output decoding.
+pub(crate) struct TokenDecoder {
+    tokenizer: dynamo_tokenizers::Tokenizer,
+}
+
+pub(super) struct DecodeState {
+    decoder: dynamo_tokenizers::DecodeStream,
+    stops: Option<StopStringMatcher>,
+    logprob_text: bool,
+}
+
+impl TokenDecoder {
+    pub(crate) fn new(tokenizer: dynamo_tokenizers::Tokenizer) -> Self {
+        Self { tokenizer }
+    }
+
+    pub(crate) fn detokenize_prompt(&self, token_ids: TokenIds) -> Result<String, ResponseError> {
+        let ids = token_ids
+            .into_iter()
+            .map(u32::try_from)
+            .collect::<Result<Vec<_>, _>>()
+            .map_err(|_| invalid("token IDs must be non-negative"))?;
+        self.tokenizer
+            .decode(&ids, true)
+            .map(String::from)
+            .map_err(|error| invalid(format!("detokenizing prompt failed: {error}")))
+    }
+
+    pub(super) fn prepare(
+        &self,
+        request: &mut GenerateRequest,
+    ) -> Result<DecodeState, ResponseError> {
+        let stops = text_stop_matcher(request);
+        let prompt_ids = request
+            .input_ids
+            .iter()
+            .map(|&id| u32::try_from(id))
+            .collect::<Result<Vec<_>, _>>()
+            .map_err(|_| invalid("input_ids must be non-negative"))?;
+        let logprob_text = request.return_text_in_logprobs.unwrap_or(false);
+        request.return_text_in_logprobs = Some(false);
+        Ok(DecodeState {
+            decoder: self
+                .tokenizer
+                .decode_stream(&prompt_ids, request.sampling_params.skip_special_tokens),
+            stops,
+            logprob_text,
+        })
+    }
+
+    pub(super) fn decode(
+        &self,
+        mut tokens: TokenStream,
+        mut state: DecodeState,
+    ) -> GenerationStream {
+        let tokenizer = self.tokenizer.clone();
+        async_stream::try_stream! {
+            while let Some(delta) = tokens.next().await {
+                let mut output = GenerationOutput::from(delta?);
+                let matched = decode_output(&mut state.decoder, &mut output, state.stops.as_mut())?;
+                if state.logprob_text {
+                    fill_logprob_text(&tokenizer, output.extras.as_deref_mut());
+                }
+                let stopped = matched.is_some();
+                if let Some(stop) = matched {
+                    output.finish_reason = Some(GenerationFinishReason::Stop(Some(MatchedStop::Text(stop))));
+                }
+                if stopped {
+                    drop(tokens);
+                    yield output;
+                    return;
+                }
+                yield output;
+            }
+        }.boxed()
+    }
+}
+
+/// Match text stops locally without removing them from the engine request.
+///
+/// The engine uses the same stops to end decoding promptly. The renderer still
+/// needs its own matcher because it owns text decoding, stop trimming, and the
+/// OpenAI-facing finish reason.
+pub(super) fn text_stop_matcher(request: &GenerateRequest) -> Option<StopStringMatcher> {
+    let params = &request.sampling_params;
+    StopStringMatcher::new(params.stop.clone(), params.no_stop_trim)
+}
+
+pub(super) struct StopStringMatcher {
+    stops: Vec<String>,
+    pending: String,
+    include_stop: bool,
+}
+
+struct StopMatch {
+    text: String,
+    matched: Option<String>,
+}
+
+impl StopStringMatcher {
+    fn new(stops: Vec<String>, include_stop: bool) -> Option<Self> {
+        (!stops.is_empty()).then_some(Self {
+            stops,
+            pending: String::new(),
+            include_stop,
+        })
+    }
+
+    fn push(&mut self, text: &str) -> StopMatch {
+        self.pending.push_str(text);
+        if let Some((position, stop)) = self
+            .stops
+            .iter()
+            .filter_map(|stop| {
+                self.pending
+                    .find(stop)
+                    .map(|position| (position, stop.clone()))
+            })
+            .min_by_key(|(position, _)| *position)
+        {
+            if stop.is_empty() {
+                return StopMatch {
+                    text: std::mem::take(&mut self.pending),
+                    matched: Some(stop),
+                };
+            }
+            let end = if self.include_stop {
+                position + stop.len()
+            } else {
+                position
+            };
+            let text = self.pending[..end].to_owned();
+            self.pending.clear();
+            return StopMatch {
+                text,
+                matched: Some(stop),
+            };
+        }
+
+        let held_start = self
+            .pending
+            .char_indices()
+            .map(|(start, _)| start)
+            .chain(std::iter::once(self.pending.len()))
+            .find(|&start| {
+                self.stops
+                    .iter()
+                    .any(|stop| stop.starts_with(&self.pending[start..]))
+            })
+            .unwrap_or(self.pending.len());
+        let held = self.pending.split_off(held_start);
+        let text = std::mem::replace(&mut self.pending, held);
+        StopMatch {
+            text,
+            matched: None,
+        }
+    }
+
+    fn flush(&mut self) -> String {
+        std::mem::take(&mut self.pending)
+    }
+}
+
+pub(super) fn decode_output(
+    decoder: &mut dynamo_tokenizers::DecodeStream,
+    output: &mut GenerationOutput,
+    mut stop_matcher: Option<&mut StopStringMatcher>,
+) -> Result<Option<String>, ResponseError> {
+    let mut text = String::new();
+    for index in 0..output.token_ids.len() {
+        let id = output.token_ids[index];
+        let id = u32::try_from(id).map_err(|_| internal("engine returned a negative token ID"))?;
+        let delta = decoder
+            .step(id)
+            .map_err(|error| internal(format!("detokenizing engine output failed: {error}")))?;
+        if let Some(matcher) = stop_matcher.as_deref_mut() {
+            let matched = matcher.push(delta.as_deref().unwrap_or_default());
+            text.push_str(&matched.text);
+            if let Some(stop) = matched.matched {
+                truncate_output(output, index + 1)?;
+                output.text = text;
+                return Ok(Some(stop));
+            }
+        } else if let Some(delta) = delta {
+            text.push_str(&delta);
+        }
+    }
+    if output.finish_reason.is_some()
+        && let Some(matcher) = stop_matcher
+    {
+        text.push_str(&matcher.flush());
+    }
+    output.text = text;
+    Ok(None)
+}
+
+fn truncate_output(output: &mut GenerationOutput, kept_tokens: usize) -> Result<(), ResponseError> {
+    output.token_ids.truncate(kept_tokens);
+    output.completion_tokens = u64::try_from(kept_tokens).unwrap_or(u64::MAX);
+    let Some(extras) = output.extras.as_deref_mut() else {
+        return Ok(());
+    };
+    truncate_optional(
+        &mut extras.output_logprobs,
+        kept_tokens,
+        "output logprob positions",
+    )
+}
+
+fn truncate_optional<T>(
+    values: &mut Vec<T>,
+    length: usize,
+    description: &str,
+) -> Result<(), ResponseError> {
+    if values.is_empty() {
+        return Ok(());
+    }
+    if values.len() < length {
+        return Err(internal(format!(
+            "engine returned {} {description} values for {length} retained tokens",
+            values.len()
+        )));
+    }
+    values.truncate(length);
+    Ok(())
+}
+
+pub(super) fn fill_logprob_text(
+    tokenizer: &dynamo_tokenizers::Tokenizer,
+    extras: Option<&mut GenerationOutputExtras>,
+) {
+    let Some(extras) = extras else { return };
+    for position in extras
+        .output_logprobs
+        .iter_mut()
+        .chain(&mut extras.input_logprobs)
+    {
+        fill_text(tokenizer, &mut position.token);
+        for token in &mut position.top {
+            fill_text(tokenizer, token);
+        }
+    }
+}
+
+fn fill_text(tokenizer: &dynamo_tokenizers::Tokenizer, token: &mut TokenLogprob) {
+    if token.text.is_some() {
+        return;
+    }
+    token.text = Some(
+        u32::try_from(token.token_id)
+            .ok()
+            .and_then(|id| tokenizer.decode(&[id], false).ok())
+            .map(String::from)
+            .unwrap_or_default(),
+    );
+}
+
+#[cfg(test)]
+mod tests {
+    use super::super::test_utils::{position, tiny_tokenizer};
+    use super::*;
+    use crate::{GenerationOptions, SamplingParams, TokenIdsRequest};
+
+    fn request(stop: Vec<&str>) -> GenerateRequest {
+        TokenIdsRequest {
+            rid: "r".into(),
+            input_ids: vec![1],
+            options: GenerationOptions {
+                sampling_params: SamplingParams {
+                    stop_strs: stop.into_iter().map(str::to_owned).collect(),
+                    ..Default::default()
+                },
+                ..Default::default()
+            },
+            metadata: Default::default(),
+        }
+        .into()
+    }
+
+    #[test]
+    fn text_stops_reach_the_frontend_and_engine() {
+        let mut request = request(vec!["<eos>"]);
+        request.sampling_params.stop_token_ids = Some(vec![9]);
+        let matcher = text_stop_matcher(&request);
+
+        assert!(matcher.is_some());
+        assert_eq!(request.sampling_params.stop_token_ids, Some(vec![9]));
+        assert_eq!(request.sampling_params.stop, ["<eos>"]);
+    }
+
+    #[test]
+    fn regex_stops_and_min_tokens_reach_the_engine() {
+        let mut request = request(vec!["END"]);
+        request.sampling_params.stop_regex = vec!["[0-9]{3}".into()];
+        request.sampling_params.min_new_tokens = 4;
+
+        text_stop_matcher(&request);
+
+        assert_eq!(request.sampling_params.stop, ["END"]);
+        assert_eq!(request.sampling_params.stop_regex, ["[0-9]{3}"]);
+        assert_eq!(request.sampling_params.min_new_tokens, 4);
+    }
+
+    #[test]
+    fn decoded_stop_matcher_handles_cross_frame_matches_and_order() {
+        let mut matcher = StopStringMatcher::new(vec!["END".into(), "ND".into()], false).unwrap();
+
+        let first = matcher.push("value E");
+        assert_eq!(first.text, "value ");
+        assert!(first.matched.is_none());
+
+        let second = matcher.push("ND trailing");
+        assert_eq!(second.text, "");
+        assert_eq!(second.matched.as_deref(), Some("END"));
+    }
+
+    #[test]
+    fn decoded_stop_matcher_uses_the_earliest_match() {
+        let mut matcher =
+            StopStringMatcher::new(vec!["later".into(), "first".into()], false).unwrap();
+
+        let matched = matcher.push("first then later");
+
+        assert_eq!(matched.text, "");
+        assert_eq!(matched.matched.as_deref(), Some("first"));
+    }
+
+    #[test]
+    fn no_stop_trim_includes_the_matched_text() {
+        let mut matcher = StopStringMatcher::new(vec!["END".into()], true).unwrap();
+        let matched = matcher.push("value END trailing");
+
+        assert_eq!(matched.text, "value END");
+        assert_eq!(matched.matched.as_deref(), Some("END"));
+    }
+
+    #[test]
+    fn local_stop_truncates_token_aligned_logprobs() {
+        let mut output = GenerationOutput {
+            token_ids: vec![7, 8, 9],
+            completion_tokens: 3,
+            extras: Some(Box::new(GenerationOutputExtras {
+                output_logprobs: vec![
+                    position(7, -0.1, &[(7, -0.1), (6, -1.0)]),
+                    position(8, -0.2, &[(8, -0.2)]),
+                    position(9, -0.3, &[(9, -0.3)]),
+                ],
+                ..Default::default()
+            })),
+            ..Default::default()
+        };
+
+        truncate_output(&mut output, 2).unwrap();
+
+        assert_eq!(output.token_ids, [7, 8]);
+        assert_eq!(output.completion_tokens, 2);
+        let extras = output.extras.unwrap();
+        assert_eq!(extras.output_logprobs.len(), 2);
+        assert_eq!(extras.output_logprobs[0].top.len(), 2);
+        assert_eq!(extras.output_logprobs[1].top.len(), 1);
+        assert_eq!(extras.output_logprobs[1].token.token_id, 8);
+    }
+
+    #[test]
+    fn text_stops_are_matched_on_contextual_decoder_output() {
+        let tokenizer = tiny_tokenizer();
+        let token_ids = tokenizer
+            .encode("hello")
+            .unwrap()
+            .token_ids()
+            .iter()
+            .map(|&id| id as i32)
+            .collect::<Vec<_>>();
+        let mut expected_decoder = tokenizer.decode_stream(&[65], true);
+        let mut decoded = String::new();
+        for &id in &token_ids {
+            if let Some(delta) = expected_decoder.step(id as u32).unwrap() {
+                decoded.push_str(&delta);
+            }
+        }
+        assert!(!decoded.is_empty());
+
+        let mut decoder = tokenizer.decode_stream(&[65], true);
+        let mut output = GenerationOutput {
+            token_ids,
+            completion_tokens: 1,
+            ..Default::default()
+        };
+        let mut matcher = StopStringMatcher::new(vec![decoded.clone()], false).unwrap();
+
+        let matched = decode_output(&mut decoder, &mut output, Some(&mut matcher)).unwrap();
+
+        assert_eq!(matched.as_deref(), Some(decoded.as_str()));
+        assert!(output.text.is_empty());
+    }
+
+    #[test]
+    fn empty_stop_matches_after_the_first_generated_token() {
+        let tokenizer = tiny_tokenizer();
+        let mut decoder = tokenizer.decode_stream(&[65], true);
+        let mut output = GenerationOutput {
+            token_ids: vec![104, 101],
+            completion_tokens: 2,
+            ..Default::default()
+        };
+        let mut matcher = StopStringMatcher::new(vec!["never".into(), String::new()], false)
+            .expect("the empty stop must remain active");
+
+        let matched = decode_output(&mut decoder, &mut output, Some(&mut matcher)).unwrap();
+
+        assert_eq!(matched.as_deref(), Some(""));
+        assert_eq!(output.token_ids, [104]);
+        assert_eq!(output.completion_tokens, 1);
+        assert_eq!(output.text, "h");
+    }
+}

rust/sglang-renderer/src/engine/http/mod.rs

@@ -0,0 +1,550 @@
+//! HTTP client from renderer-owned generation requests to SGLang `/generate`.
+
+use std::time::Duration;
+
+use async_stream::stream;
+use futures::{StreamExt, future::BoxFuture};
+
+use super::{GenerateTransport, TokenStream, internal};
+use crate::{GenerateRequest, ResponseError};
+use protocol::{engine_error_message, normalize_engine_output, parse_engine_frame};
+
+mod protocol;
+
+// SGLang's deep health probe defaults to 20 seconds. Leave it time to return
+// its own status while still bounding a peer that never sends response headers.
+const ENGINE_HEALTH_REQUEST_TIMEOUT: Duration = Duration::from_secs(30);
+
+fn unavailable(message: impl Into<String>) -> ResponseError {
+    ResponseError {
+        kind: crate::ResponseErrorKind::Unavailable,
+        message: message.into(),
+    }
+}
+
+#[derive(Clone)]
+pub struct HttpGenerateClient {
+    client: reqwest::Client,
+    generate_url: reqwest::Url,
+    health_url: reqwest::Url,
+    health_timeout: Duration,
+}
+
+impl HttpGenerateClient {
+    pub fn new(engine_url: impl AsRef<str>) -> Result<Self, String> {
+        let engine_url = engine_url.as_ref();
+        let base_url = reqwest::Url::parse(engine_url)
+            .map_err(|error| format!("invalid engine URL {engine_url:?}: {error}"))?;
+        let is_http_origin = matches!(base_url.scheme(), "http" | "https")
+            && base_url.host_str().is_some()
+            && base_url.username().is_empty()
+            && base_url.password().is_none()
+            && base_url.path() == "/"
+            && base_url.query().is_none()
+            && base_url.fragment().is_none();
+        if !is_http_origin {
+            return Err(format!(
+                "invalid engine URL {engine_url:?}: expected an HTTP(S) origin without credentials, a path, query, or fragment"
+            ));
+        }
+        let generate_url = base_url
+            .join("/generate")
+            .map_err(|error| format!("joining /generate to engine URL failed: {error}"))?;
+        let health_url = base_url
+            .join("/health")
+            .map_err(|error| format!("joining /health to engine URL failed: {error}"))?;
+        let client = reqwest::Client::builder()
+            .connect_timeout(Duration::from_secs(10))
+            .build()
+            .map_err(|error| format!("building engine HTTP client failed: {error}"))?;
+        Ok(Self {
+            client,
+            generate_url,
+            health_url,
+            health_timeout: ENGINE_HEALTH_REQUEST_TIMEOUT,
+        })
+    }
+
+    #[cfg(test)]
+    pub(crate) fn with_health_timeout(mut self, timeout: Duration) -> Self {
+        self.health_timeout = timeout;
+        self
+    }
+
+    pub(crate) async fn health_status(&self) -> Result<reqwest::StatusCode, ResponseError> {
+        let request = self
+            .client
+            .get(self.health_url.clone())
+            .timeout(self.health_timeout);
+        let response = request
+            .send()
+            .await
+            .map_err(|error| unavailable(format!("engine health check failed: {error}")))?;
+        Ok(response.status())
+    }
+}
+
+impl GenerateTransport for HttpGenerateClient {
+    fn generate(
+        &self,
+        mut request: GenerateRequest,
+    ) -> BoxFuture<'_, Result<TokenStream, ResponseError>> {
+        Box::pin(async move {
+            // Always consume token deltas, including for unary frontend requests.
+            request.stream = true;
+
+            let response = self
+                .client
+                .post(self.generate_url.clone())
+                .json(&request)
+                .send()
+                .await
+                .map_err(|error| unavailable(format!("engine request failed: {error}")))?;
+            let status = response.status();
+            if !status.is_success() {
+                let body = response.text().await.unwrap_or_default();
+                return Err(ResponseError {
+                    kind: crate::ResponseErrorKind::Upstream(crate::UpstreamErrorCode::Http(
+                        status.as_u16(),
+                    )),
+                    message: engine_error_message(&body)
+                        .unwrap_or_else(|| format!("engine returned HTTP {status}")),
+                });
+            }
+
+            let mut chunks = response.bytes_stream();
+            let events = stream! {
+                let mut parser = SseParser::default();
+                let mut terminal = false;
+                let mut emitted_tokens = 0;
+                while let Some(chunk) = chunks.next().await {
+                    let chunk = match chunk {
+                        Ok(chunk) => chunk,
+                        Err(error) => {
+                            yield Err(unavailable(format!("engine stream failed: {error}")));
+                            return;
+                        }
+                    };
+                    for payload in parser.push(&chunk) {
+                        if payload == "[DONE]" {
+                            if !terminal {
+                                yield Err(internal("engine stream ended before a terminal frame"));
+                            }
+                            return;
+                        }
+                        let mut output = match parse_engine_frame(&payload) {
+                            Ok(output) => output,
+                            Err(error) => {
+                                yield Err(error);
+                                return;
+                            }
+                        };
+                        if let Err(error) = normalize_engine_output(&mut output, &mut emitted_tokens) {
+                            yield Err(error);
+                            return;
+                        }
+                        terminal = output.finish_reason.is_some();
+                        yield Ok(output);
+                    }
+                }
+                if !terminal {
+                    yield Err(internal("engine response closed before [DONE]"));
+                }
+            }
+            .boxed();
+
+            Ok(events)
+        })
+    }
+}
+
+#[derive(Default)]
+struct SseParser {
+    bytes: Vec<u8>,
+}
+
+impl SseParser {
+    fn push(&mut self, chunk: &[u8]) -> Vec<String> {
+        self.bytes.extend_from_slice(chunk);
+        let mut payloads = Vec::new();
+        while let Some((end, separator_len)) = event_end(&self.bytes) {
+            let event = self.bytes.drain(..end).collect::<Vec<_>>();
+            self.bytes.drain(..separator_len);
+            let event = String::from_utf8_lossy(&event);
+            let data = event
+                .lines()
+                .filter_map(|line| line.strip_prefix("data:").map(str::trim_start))
+                .collect::<Vec<_>>()
+                .join("\n");
+            if !data.is_empty() {
+                payloads.push(data);
+            }
+        }
+        payloads
+    }
+}
+
+fn event_end(bytes: &[u8]) -> Option<(usize, usize)> {
+    let crlf = bytes
+        .windows(4)
+        .position(|window| window == b"\r\n\r\n")
+        .map(|position| (position, 4));
+    let lf = bytes
+        .windows(2)
+        .position(|window| window == b"\n\n")
+        .map(|position| (position, 2));
+    match (crlf, lf) {
+        (Some(crlf), Some(lf)) => Some(crlf.min(lf)),
+        (Some(crlf), None) => Some(crlf),
+        (None, Some(lf)) => Some(lf),
+        (None, None) => None,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::engine::test_utils::tiny_tokenizer;
+    use crate::{GenerationOptions, TokenIds, TokenIdsRequest};
+    use axum::{
+        Json, Router,
+        extract::State,
+        response::sse::{Event, Sse},
+        routing::post,
+    };
+    use std::convert::Infallible;
+    use std::sync::{Arc, Mutex};
+
+    #[test]
+    fn sse_parser_handles_split_crlf_and_lf_frames() {
+        let mut parser = SseParser::default();
+        assert!(parser.push(b"data: {\"a\":1}\r\n").is_empty());
+        assert_eq!(
+            parser.push(b"\r\ndata: [DONE]\n\n"),
+            ["{\"a\":1}", "[DONE]"]
+        );
+    }
+
+    #[test]
+    fn sse_parser_uses_the_earliest_mixed_delimiter() {
+        let mut parser = SseParser::default();
+
+        let payloads = parser.push(b"data: {\"a\":1}\n\ndata: {\"b\":2}\r\n\r\n");
+
+        assert_eq!(payloads, ["{\"a\":1}", "{\"b\":2}"]);
+    }
+
+    #[derive(Clone)]
+    struct EngineState {
+        requests: Arc<Mutex<Vec<serde_json::Value>>>,
+        output_ids: TokenIds,
+    }
+
+    async fn generate(
+        State(state): State<EngineState>,
+        Json(body): Json<serde_json::Value>,
+    ) -> Sse<impl futures::Stream<Item = Result<Event, Infallible>>> {
+        state.requests.lock().unwrap().push(body);
+        let frame = serde_json::json!({
+            "output_ids": state.output_ids,
+            "meta_info": {
+                "prompt_tokens": 1,
+                "completion_tokens": state.output_ids.len(),
+                "finish_reason": {"type": "stop", "matched": null}
+            }
+        })
+        .to_string();
+        Sse::new(futures::stream::iter([
+            Ok(Event::default().data(frame)),
+            Ok(Event::default().data("[DONE]")),
+        ]))
+    }
+
+    async fn streaming_generate(
+        State(cumulative): State<bool>,
+    ) -> Sse<impl futures::Stream<Item = Result<Event, Infallible>>> {
+        let frame = |completion_tokens, finish_reason: serde_json::Value| {
+            Event::default().data(
+                serde_json::json!({
+                    "output_ids": if cumulative { vec![104; completion_tokens] } else { vec![104] },
+                    "meta_info": {
+                        "prompt_tokens": 1,
+                        "completion_tokens": completion_tokens,
+                        "finish_reason": finish_reason,
+                    }
+                })
+                .to_string(),
+            )
+        };
+        Sse::new(futures::stream::iter([
+            Ok(frame(1, serde_json::Value::Null)),
+            Ok(frame(2, serde_json::json!({"type": "length", "length": 2}))),
+            Ok(Event::default().data("[DONE]")),
+        ]))
+    }
+
+    #[test]
+    fn engine_origins_are_validated_and_joined_during_client_construction() {
+        for invalid_url in [
+            "127.0.0.1:30001",
+            "ftp://engine.example",
+            "http://user@engine.example",
+            "http://engine.example/base",
+            "http://engine.example?query",
+            "http://engine.example#fragment",
+        ] {
+            let error = match HttpGenerateClient::new(invalid_url) {
+                Ok(_) => panic!("{invalid_url:?} must be rejected"),
+                Err(error) => error,
+            };
+            assert!(error.contains("invalid engine URL"));
+        }
+
+        let client = HttpGenerateClient::new("http://engine.example:30001/").unwrap();
+        assert_eq!(
+            client.generate_url.as_str(),
+            "http://engine.example:30001/generate"
+        );
+        assert_eq!(
+            client.health_url.as_str(),
+            "http://engine.example:30001/health"
+        );
+    }
+
+    #[tokio::test]
+    async fn backend_posts_token_ids_and_decodes_the_engine_stream() {
+        let tokenizer = tiny_tokenizer();
+        let output_ids = tokenizer
+            .encode("hello")
+            .unwrap()
+            .token_ids()
+            .iter()
+            .map(|&id| id as i32)
+            .collect::<Vec<_>>();
+        let requests = Arc::new(Mutex::new(Vec::new()));
+        let listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
+        let address = listener.local_addr().unwrap();
+        let server = tokio::spawn(
+            axum::serve(
+                listener,
+                Router::new()
+                    .route("/generate", post(generate))
+                    .with_state(EngineState {
+                        requests: requests.clone(),
+                        output_ids: output_ids.clone(),
+                    }),
+            )
+            .into_future(),
+        );
+
+        let client = HttpGenerateClient::new(format!("http://{address}")).unwrap();
+        let request = TokenIdsRequest {
+            rid: "client-request".into(),
+            input_ids: vec![65],
+            options: GenerationOptions {
+                return_text_in_logprobs: Some(true),
+                ..Default::default()
+            },
+            metadata: Default::default(),
+        };
+        let service = crate::engine::GenerationService::new(
+            Arc::new(client),
+            crate::engine::TokenDecoder::new(tokenizer.clone()),
+        );
+        let mut events = service.generate(request.into()).await.unwrap();
+        let output = events.next().await.unwrap().unwrap();
+        assert!(output.finish_reason.is_some());
+
+        let mut expected_decoder = tokenizer.decode_stream(&[65], true);
+        let mut expected = String::new();
+        for id in output_ids {
+            if let Some(delta) = expected_decoder.step(id as u32).unwrap() {
+                expected.push_str(&delta);
+            }
+        }
+        assert_eq!(output.text, expected);
+        assert_eq!(output.prompt_tokens, 1);
+        let request = requests.lock().unwrap().pop().unwrap();
+        assert_eq!(request["rid"], "client-request");
+        assert_eq!(request["input_ids"], serde_json::json!([65]));
+        assert_eq!(request["stream"], true);
+        assert!(request.get("incremental_streaming_output").is_none());
+        assert_eq!(request["return_text_in_logprobs"], false);
+        server.abort();
+    }
+
+    #[tokio::test]
+    async fn transport_requires_a_terminal_frame_and_rejects_malformed_output() {
+        async fn scripted(
+            Json(request): Json<serde_json::Value>,
+        ) -> Sse<impl futures::Stream<Item = Result<Event, Infallible>>> {
+            let case = request["rid"].as_str().unwrap();
+            let terminal = case == "terminal-eof";
+            let frame = serde_json::json!({
+                "output_ids": [],
+                "meta_info": {
+                    "prompt_tokens": 1,
+                    "completion_tokens": 0,
+                    "finish_reason": if terminal { serde_json::json!({"type": "length"}) } else { serde_json::Value::Null },
+                }
+            }).to_string();
+            let frames = match case {
+                "malformed" => vec!["{".to_owned()],
+                "early-done" => vec![frame, "[DONE]".to_owned()],
+                _ => vec![frame],
+            };
+            Sse::new(futures::stream::iter(
+                frames
+                    .into_iter()
+                    .map(|frame| Ok(Event::default().data(frame))),
+            ))
+        }
+        let listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
+        let address = listener.local_addr().unwrap();
+        let server = tokio::spawn(
+            axum::serve(listener, Router::new().route("/generate", post(scripted))).into_future(),
+        );
+        let client = HttpGenerateClient::new(format!("http://{address}")).unwrap();
+        for (case, error_message) in [
+            ("malformed", Some("invalid engine frame")),
+            (
+                "early-done",
+                Some("engine stream ended before a terminal frame"),
+            ),
+            (
+                "unfinished-eof",
+                Some("engine response closed before [DONE]"),
+            ),
+            ("terminal-eof", None),
+        ] {
+            let request = TokenIdsRequest {
+                rid: case.into(),
+                input_ids: vec![65],
+                options: GenerationOptions::default(),
+                metadata: Default::default(),
+            };
+            let events = client
+                .generate(request.into())
+                .await
+                .unwrap()
+                .collect::<Vec<_>>()
+                .await;
+            if let Some(message) = error_message {
+                let error = events.last().unwrap().as_ref().unwrap_err();
+                assert_eq!(error.kind, crate::ResponseErrorKind::Internal);
+                assert!(
+                    error.message.starts_with(message),
+                    "{case}: {}",
+                    error.message
+                );
+                assert_eq!(events.iter().filter(|event| event.is_err()).count(), 1);
+            } else {
+                assert_eq!(events.len(), 1);
+                assert!(events[0].as_ref().unwrap().finish_reason.is_some());
+            }
+        }
+        server.abort();
+    }
+
+    #[tokio::test]
+    async fn engine_frames_are_forwarded_once() {
+        for cumulative in [false, true] {
+            let listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
+            let address = listener.local_addr().unwrap();
+            let server = tokio::spawn(
+                axum::serve(
+                    listener,
+                    Router::new()
+                        .route("/generate", post(streaming_generate))
+                        .with_state(cumulative),
+                )
+                .into_future(),
+            );
+
+            let client = HttpGenerateClient::new(format!("http://{address}")).unwrap();
+            let mut events = client
+                .generate(
+                    TokenIdsRequest {
+                        rid: "incremental".into(),
+                        input_ids: vec![65],
+                        options: GenerationOptions::default(),
+                        metadata: Default::default(),
+                    }
+                    .into(),
+                )
+                .await
+                .unwrap();
+
+            let first = events.next().await.unwrap().unwrap();
+            assert!(first.finish_reason.is_none());
+            assert_eq!(first.token_ids, [104]);
+            assert_eq!(first.completion_tokens, 1);
+
+            let second = events.next().await.unwrap().unwrap();
+            assert!(second.finish_reason.is_some());
+            assert_eq!(second.token_ids, [104]);
+            assert_eq!(second.completion_tokens, 1);
+            assert!(events.next().await.is_none());
+            server.abort();
+        }
+    }
+
+    struct DropNotice(Option<tokio::sync::oneshot::Sender<()>>);
+
+    impl Drop for DropNotice {
+        fn drop(&mut self) {
+            if let Some(sender) = self.0.take() {
+                let _ = sender.send(());
+            }
+        }
+    }
+
+    async fn slow_generate(
+        State(notice): State<Arc<Mutex<Option<tokio::sync::oneshot::Sender<()>>>>>,
+    ) -> Sse<impl futures::Stream<Item = Result<Event, Infallible>>> {
+        let guard = DropNotice(notice.lock().unwrap().take());
+        Sse::new(stream! {
+            let _guard = guard;
+            yield Ok(Event::default().data(serde_json::json!({
+                "output_ids": [104],
+                "meta_info": {
+                    "prompt_tokens": 1,
+                    "completion_tokens": 1,
+                    "finish_reason": null
+                }
+            }).to_string()));
+            futures::future::pending::<()>().await;
+        })
+    }
+
+    #[tokio::test]
+    async fn dropping_renderer_events_closes_the_engine_stream() {
+        let (notice_tx, notice_rx) = tokio::sync::oneshot::channel();
+        let listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
+        let address = listener.local_addr().unwrap();
+        let server = tokio::spawn(
+            axum::serve(
+                listener,
+                Router::new()
+                    .route("/generate", post(slow_generate))
+                    .with_state(Arc::new(Mutex::new(Some(notice_tx)))),
+            )
+            .into_future(),
+        );
+        let client = HttpGenerateClient::new(format!("http://{address}")).unwrap();
+        let request = TokenIdsRequest {
+            rid: "cancel-me".into(),
+            input_ids: vec![65],
+            options: GenerationOptions::default(),
+            metadata: Default::default(),
+        };
+        let mut events = client.generate(request.into()).await.unwrap();
+        assert!(events.next().await.is_some());
+        drop(events);
+        tokio::time::timeout(Duration::from_secs(2), notice_rx)
+            .await
+            .expect("engine response stream was not dropped")
+            .unwrap();
+        server.abort();
+    }
+}

rust/sglang-renderer/src/engine/http/protocol.rs

@@ -0,0 +1,455 @@
+//! SGLang engine frame parsing and normalization into generation deltas.
+
+use super::internal;
+use crate::engine::TokenDelta;
+use crate::{
+    GenerationFinishReason, GenerationOutputExtras, MatchedStop, PositionLogprobs, ResponseError,
+    TokenIds, TokenLogprob,
+};
+use serde::Deserialize;
+
+type WireLogprob = (Option<f32>, i32, Option<String>);
+type WireTopLogprobs = Vec<Option<Vec<WireLogprob>>>;
+
+#[derive(Deserialize)]
+struct EngineFrame {
+    #[serde(default)]
+    output_ids: TokenIds,
+    meta_info: EngineMeta,
+}
+
+#[derive(Deserialize)]
+struct EngineMeta {
+    #[serde(default)]
+    prompt_tokens: u32,
+    #[serde(default)]
+    completion_tokens: u64,
+    #[serde(default)]
+    finish_reason: Option<EngineFinishReason>,
+    #[serde(default)]
+    output_token_logprobs: Vec<WireLogprob>,
+    #[serde(default)]
+    input_token_logprobs: Vec<WireLogprob>,
+    #[serde(default)]
+    output_top_logprobs: WireTopLogprobs,
+    #[serde(default)]
+    input_top_logprobs: WireTopLogprobs,
+}
+
+#[derive(Deserialize)]
+struct EngineFinishReason {
+    #[serde(rename = "type")]
+    kind: String,
+    #[serde(default)]
+    matched: Option<EngineMatchedStop>,
+    #[serde(default)]
+    status_code: Option<u16>,
+    #[serde(default)]
+    message: Option<String>,
+}
+
+#[derive(Deserialize)]
+#[serde(untagged)]
+enum EngineMatchedStop {
+    Token(i64),
+    Text(String),
+    Tokens(Vec<i64>),
+}
+
+#[derive(Deserialize)]
+struct EngineErrorEnvelope {
+    error: EngineError,
+}
+
+#[derive(Deserialize)]
+struct EngineError {
+    #[serde(default = "default_error_code")]
+    code: u16,
+    message: String,
+}
+
+fn default_error_code() -> u16 {
+    500
+}
+
+pub(super) fn parse_engine_frame(payload: &str) -> Result<TokenDelta, ResponseError> {
+    if let Ok(error) = serde_json::from_str::<EngineErrorEnvelope>(payload) {
+        return Err(ResponseError {
+            kind: crate::ResponseErrorKind::Upstream(crate::UpstreamErrorCode::Http(
+                error.error.code,
+            )),
+            message: error.error.message,
+        });
+    }
+    let frame: EngineFrame = serde_json::from_str(payload)
+        .map_err(|error| internal(format!("invalid engine frame: {error}")))?;
+    if let Some(reason) = frame.meta_info.finish_reason.as_ref()
+        && reason.kind == "abort"
+        && let Some(status_code) = reason.status_code
+    {
+        return Err(ResponseError {
+            kind: crate::ResponseErrorKind::Upstream(crate::UpstreamErrorCode::Http(status_code)),
+            message: reason
+                .message
+                .clone()
+                .unwrap_or_else(|| "request aborted".to_owned()),
+        });
+    }
+    let finish_reason = frame
+        .meta_info
+        .finish_reason
+        .map(|reason| match reason.kind.as_str() {
+            "stop" => GenerationFinishReason::Stop(reason.matched.map(|matched| match matched {
+                EngineMatchedStop::Token(id) => MatchedStop::Token(id),
+                EngineMatchedStop::Text(text) => MatchedStop::Text(text),
+                EngineMatchedStop::Tokens(ids) => MatchedStop::Tokens(ids),
+            })),
+            "length" => GenerationFinishReason::Length,
+            "abort" => GenerationFinishReason::Abort,
+            "content_filter" => GenerationFinishReason::ContentFilter,
+            other => GenerationFinishReason::Other(other.to_owned()),
+        });
+    let has_extras = !frame.meta_info.output_token_logprobs.is_empty()
+        || !frame.meta_info.input_token_logprobs.is_empty()
+        || !frame.meta_info.output_top_logprobs.is_empty()
+        || !frame.meta_info.input_top_logprobs.is_empty();
+    let output_logprobs = group_logprobs(
+        frame.meta_info.output_token_logprobs,
+        frame.meta_info.output_top_logprobs,
+        "output",
+    )?;
+    let input_logprobs = group_logprobs(
+        frame.meta_info.input_token_logprobs,
+        frame.meta_info.input_top_logprobs,
+        "input",
+    )?;
+    let extras = has_extras.then_some(Box::new(GenerationOutputExtras {
+        output_logprobs,
+        input_logprobs,
+    }));
+    Ok(TokenDelta {
+        token_ids: frame.output_ids,
+        finish_reason,
+        prompt_tokens: frame.meta_info.prompt_tokens,
+        completion_tokens: frame.meta_info.completion_tokens,
+        extras,
+    })
+}
+
+pub(super) fn normalize_engine_output(
+    output: &mut TokenDelta,
+    emitted_tokens: &mut u64,
+) -> Result<(), ResponseError> {
+    let total = output.completion_tokens;
+    let delta = total.checked_sub(*emitted_tokens).ok_or_else(|| {
+        internal(format!(
+            "engine completion token count decreased from {} to {total}",
+            *emitted_tokens
+        ))
+    })?;
+    let output_len = u64::try_from(output.token_ids.len()).unwrap_or(u64::MAX);
+    let trimmed_stop_tokens = match output.finish_reason.as_ref() {
+        Some(GenerationFinishReason::Stop(Some(MatchedStop::Token(_)))) => 1,
+        Some(GenerationFinishReason::Stop(Some(MatchedStop::Tokens(ids)))) => {
+            u64::try_from(ids.len()).unwrap_or(u64::MAX)
+        }
+        _ => 0,
+    };
+    let cumulative =
+        output_len == total || output_len.checked_add(trimmed_stop_tokens) == Some(total);
+    let incremental =
+        output_len == delta || output_len.checked_add(trimmed_stop_tokens) == Some(delta);
+
+    if cumulative {
+        let prefix = usize::try_from(*emitted_tokens)
+            .map_err(|_| internal("engine completion token count exceeds addressable memory"))?;
+        if prefix > output.token_ids.len() {
+            return Err(internal(format!(
+                "engine returned {output_len} cumulative output token IDs after {prefix} were already emitted"
+            )));
+        }
+        output.token_ids.drain(..prefix);
+        if let Some(extras) = output.extras.as_deref_mut() {
+            trim_cumulative_output_extras(extras, prefix)?;
+        }
+    } else if !incremental {
+        return Err(internal(format!(
+            "engine returned {output_len} output token IDs after reporting {delta} new completion tokens"
+        )));
+    }
+
+    output.completion_tokens = delta;
+    *emitted_tokens = total;
+    Ok(())
+}
+
+fn trim_cumulative_output_extras(
+    extras: &mut GenerationOutputExtras,
+    prefix: usize,
+) -> Result<(), ResponseError> {
+    drain_optional_prefix(
+        &mut extras.output_logprobs,
+        prefix,
+        "output logprob positions",
+    )
+}
+
+fn drain_prefix<T>(
+    values: &mut Vec<T>,
+    prefix: usize,
+    description: &str,
+) -> Result<(), ResponseError> {
+    if values.len() < prefix {
+        return Err(internal(format!(
+            "engine returned {} {description} values for a {prefix}-token cumulative prefix",
+            values.len()
+        )));
+    }
+    values.drain(..prefix);
+    Ok(())
+}
+
+fn drain_optional_prefix<T>(
+    values: &mut Vec<T>,
+    prefix: usize,
+    description: &str,
+) -> Result<(), ResponseError> {
+    if values.is_empty() {
+        return Ok(());
+    }
+    drain_prefix(values, prefix, description)
+}
+
+fn wire_logprob((logprob, token_id, text): WireLogprob) -> TokenLogprob {
+    TokenLogprob {
+        logprob,
+        token_id,
+        text,
+    }
+}
+
+fn group_logprobs(
+    values: Vec<WireLogprob>,
+    top_values: WireTopLogprobs,
+    kind: &str,
+) -> Result<Vec<PositionLogprobs>, ResponseError> {
+    // P/D can send a single null position when top logprobs are disabled.
+    if top_values.iter().all(Option::is_none) {
+        return Ok(values
+            .into_iter()
+            .map(|token| PositionLogprobs {
+                token: wire_logprob(token),
+                top: Vec::new(),
+            })
+            .collect());
+    }
+
+    if top_values.len() != values.len() {
+        return Err(internal(format!(
+            "engine returned {} {kind} top-logprob positions for {} selected-token positions",
+            top_values.len(),
+            values.len()
+        )));
+    }
+
+    Ok(values
+        .into_iter()
+        .zip(top_values)
+        .map(|(token, top)| PositionLogprobs {
+            token: wire_logprob(token),
+            top: top
+                .unwrap_or_default()
+                .into_iter()
+                .map(wire_logprob)
+                .collect(),
+        })
+        .collect())
+}
+
+pub(super) fn engine_error_message(body: &str) -> Option<String> {
+    serde_json::from_str::<EngineErrorEnvelope>(body)
+        .ok()
+        .map(|error| error.error.message)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::engine::test_utils::position;
+
+    #[test]
+    fn engine_frame_maps_tokens_usage_finish_and_logprobs() {
+        let output = parse_engine_frame(
+            r#"{
+                "output_ids":[7],
+                "meta_info":{
+                    "prompt_tokens":3,
+                    "completion_tokens":1,
+                    "finish_reason":{"type":"stop","matched":9},
+                    "output_token_logprobs":[[-0.25,7,null]],
+                    "output_top_logprobs":[[[-0.25,7,null],[-1.0,8,null]]]
+                }
+            }"#,
+        )
+        .unwrap();
+        assert_eq!(output.token_ids, [7]);
+        assert_eq!(output.prompt_tokens, 3);
+        assert_eq!(output.completion_tokens, 1);
+        assert_eq!(
+            output.finish_reason,
+            Some(GenerationFinishReason::Stop(Some(MatchedStop::Token(9))))
+        );
+        let extras = output.extras.unwrap();
+        assert_eq!(extras.output_logprobs.len(), 1);
+        assert_eq!(extras.output_logprobs[0].token.token_id, 7);
+        assert_eq!(extras.output_logprobs[0].top.len(), 2);
+    }
+
+    #[test]
+    fn engine_frame_preserves_selected_logprobs_with_absent_top_positions() {
+        let output = parse_engine_frame(
+            r#"{
+                "output_ids":[12095,13],
+                "meta_info":{
+                    "prompt_tokens":5,
+                    "completion_tokens":2,
+                    "output_token_logprobs":[
+                        [-0.42652416229248047,12095,null],
+                        [-0.7053262591362,13,null]
+                    ],
+                    "output_top_logprobs":[null]
+                }
+            }"#,
+        )
+        .unwrap();
+
+        assert_eq!(output.token_ids, [12095, 13]);
+        assert_eq!(
+            output.extras.unwrap().output_logprobs,
+            [
+                position(12095, -0.42652416, &[]),
+                position(13, -0.70532626, &[])
+            ]
+        );
+    }
+
+    #[test]
+    fn engine_frame_rejects_misaligned_logprob_positions() {
+        let error = parse_engine_frame(
+            r#"{
+                "output_ids":[7,8],
+                "meta_info":{
+                    "completion_tokens":2,
+                    "output_token_logprobs":[[-0.25,7,null],[-0.5,8,null]],
+                    "output_top_logprobs":[[[-0.25,7,null]]]
+                }
+            }"#,
+        )
+        .unwrap_err();
+
+        assert_eq!(error.kind, crate::ResponseErrorKind::Internal);
+        assert_eq!(
+            error.message,
+            "engine returned 1 output top-logprob positions for 2 selected-token positions"
+        );
+    }
+
+    #[test]
+    fn engine_error_frame_preserves_status_and_message() {
+        let error = parse_engine_frame(
+            r#"{"error":{"message":"too long","type":"BadRequestError","code":400}}"#,
+        )
+        .unwrap_err();
+        assert_eq!(
+            error.kind,
+            crate::ResponseErrorKind::Upstream(crate::UpstreamErrorCode::Http(400))
+        );
+        assert_eq!(error.message, "too long");
+    }
+
+    #[test]
+    fn coded_abort_frame_preserves_status_and_message() {
+        let error = parse_engine_frame(
+            r#"{"output_ids":[],"meta_info":{"finish_reason":{"type":"abort","status_code":503,"message":"out of memory"}}}"#,
+        )
+        .unwrap_err();
+
+        assert_eq!(
+            error.kind,
+            crate::ResponseErrorKind::Upstream(crate::UpstreamErrorCode::Http(503))
+        );
+        assert_eq!(error.message, "out of memory");
+    }
+
+    #[test]
+    fn uncoded_abort_frame_remains_a_finish_reason() {
+        let output = parse_engine_frame(
+            r#"{"output_ids":[],"meta_info":{"finish_reason":{"type":"abort","status_code":null,"message":"cancelled"}}}"#,
+        )
+        .unwrap();
+
+        assert_eq!(output.finish_reason, Some(GenerationFinishReason::Abort));
+    }
+
+    #[test]
+    fn cumulative_engine_frames_become_deltas() {
+        let mut emitted_tokens = 1;
+        let mut output = TokenDelta {
+            token_ids: vec![7, 8],
+            completion_tokens: 2,
+            extras: Some(Box::new(GenerationOutputExtras {
+                output_logprobs: vec![
+                    position(7, -0.5, &[(7, -0.5), (9, -1.0)]),
+                    position(8, -0.25, &[(8, -0.25)]),
+                ],
+                ..Default::default()
+            })),
+            ..Default::default()
+        };
+
+        normalize_engine_output(&mut output, &mut emitted_tokens).unwrap();
+
+        assert_eq!(output.token_ids, [8]);
+        assert_eq!(output.completion_tokens, 1);
+        assert_eq!(emitted_tokens, 2);
+        let extras = output.extras.unwrap();
+        assert_eq!(extras.output_logprobs.len(), 1);
+        assert_eq!(extras.output_logprobs[0].token.token_id, 8);
+        assert_eq!(extras.output_logprobs[0].top.len(), 1);
+    }
+
+    #[test]
+    fn token_stops_may_be_trimmed_from_incremental_or_cumulative_frames() {
+        for token_ids in [vec![], vec![7]] {
+            let mut emitted_tokens = 1;
+            let mut output = TokenDelta {
+                token_ids,
+                completion_tokens: 2,
+                finish_reason: Some(GenerationFinishReason::Stop(Some(MatchedStop::Token(9)))),
+                ..Default::default()
+            };
+
+            normalize_engine_output(&mut output, &mut emitted_tokens).unwrap();
+
+            assert!(output.token_ids.is_empty());
+            assert_eq!(output.completion_tokens, 1);
+            assert_eq!(emitted_tokens, 2);
+        }
+    }
+
+    #[test]
+    fn inconsistent_engine_token_counts_are_rejected() {
+        let mut emitted_tokens = 2;
+        let mut output = TokenDelta {
+            token_ids: vec![7, 8],
+            completion_tokens: 3,
+            ..Default::default()
+        };
+
+        let error = normalize_engine_output(&mut output, &mut emitted_tokens).unwrap_err();
+
+        assert_eq!(error.kind, crate::ResponseErrorKind::Internal);
+        assert!(error.message.contains("2 output token IDs"));
+        assert_eq!(emitted_tokens, 2);
+    }
+}

rust/sglang-renderer/src/engine/mod.rs

@@ -0,0 +1,91 @@
+//! Token-only generation transport and decoded engine output.
+
+use futures::{StreamExt, TryStreamExt, future::BoxFuture};
+
+use crate::{GenerateRequest, ResponseError};
+
+mod decode;
+#[cfg(feature = "http")]
+mod http;
+pub(crate) mod response;
+mod types;
+
+pub(crate) use decode::TokenDecoder;
+#[cfg(feature = "http")]
+pub(crate) use http::HttpGenerateClient;
+pub(crate) use types::{
+    GenerationFinishReason, GenerationOutput, GenerationOutputExtras, GenerationStream,
+    MatchedStop, PositionLogprobs, TokenDelta, TokenLogprob,
+};
+
+pub(crate) type TokenStream =
+    futures::stream::BoxStream<'static, Result<TokenDelta, ResponseError>>;
+
+/// Backend generation from prepared token requests to normalized token deltas.
+///
+/// Successful streams carry a finish reason on their terminal output. The caller
+/// owns the submission future and response stream; dropping either must release the
+/// corresponding transport work. HTTP health checks and proxying are separate.
+pub(crate) trait GenerateTransport: Send + Sync {
+    fn generate(
+        &self,
+        request: GenerateRequest,
+    ) -> BoxFuture<'_, Result<TokenStream, ResponseError>>;
+}
+
+// Bound pending submissions per request without duplicating scheduler admission.
+const CONCURRENT_ENGINE_SUBMISSIONS: usize = 32;
+
+/// Shared generation policy and decoding, independent of the engine transport.
+pub(crate) struct GenerationService {
+    transport: std::sync::Arc<dyn GenerateTransport>,
+    pub(crate) decoder: TokenDecoder,
+}
+
+impl GenerationService {
+    pub(crate) fn new(
+        transport: std::sync::Arc<dyn GenerateTransport>,
+        decoder: TokenDecoder,
+    ) -> Self {
+        Self { transport, decoder }
+    }
+
+    pub(crate) async fn generate(
+        &self,
+        mut request: GenerateRequest,
+    ) -> Result<GenerationStream, ResponseError> {
+        let decode = self.decoder.prepare(&mut request)?;
+        let tokens = self.transport.generate(request).await?;
+        Ok(self.decoder.decode(tokens, decode))
+    }
+
+    /// Establish all choice streams before consumption, retaining input order.
+    pub(crate) async fn generate_many(
+        &self,
+        inputs: Vec<GenerateRequest>,
+    ) -> Result<Vec<GenerationStream>, ResponseError> {
+        futures::stream::iter(inputs.into_iter().map(|input| self.generate(input)))
+            .buffered(CONCURRENT_ENGINE_SUBMISSIONS)
+            .try_collect()
+            .await
+    }
+}
+
+fn invalid(message: impl Into<String>) -> ResponseError {
+    ResponseError {
+        kind: crate::ResponseErrorKind::InvalidRequest,
+        message: message.into(),
+    }
+}
+
+fn internal(message: impl Into<String>) -> ResponseError {
+    ResponseError {
+        kind: crate::ResponseErrorKind::Internal,
+        message: message.into(),
+    }
+}
+
+#[cfg(test)]
+pub(crate) mod test_utils;
+#[cfg(test)]
+mod tests;

rust/sglang-renderer/src/engine/response.rs

@@ -0,0 +1,116 @@
+//! Generation stream merging and aggregation.
+
+use crate::{GenerationOutput, GenerationStream, ResponseError};
+use futures::{StreamExt, stream::BoxStream};
+
+pub(crate) fn merge_indexed(
+    streams: Vec<GenerationStream>,
+) -> BoxStream<'static, (usize, Result<GenerationOutput, ResponseError>)> {
+    let streams = streams
+        .into_iter()
+        .enumerate()
+        .map(|(index, events)| events.map(move |event| (index, event)).boxed());
+    futures::stream::select_all(streams).boxed()
+}
+
+pub(crate) async fn collect_output(
+    mut events: GenerationStream,
+) -> Result<GenerationOutput, ResponseError> {
+    let mut collected = GenerationOutput::default();
+    while let Some(item) = events.next().await {
+        let output = item?;
+        let finished = output.finish_reason.is_some();
+        fold_output(&mut collected, output);
+        if finished {
+            return Ok(collected);
+        }
+    }
+    Err(ResponseError {
+        kind: crate::ResponseErrorKind::Internal,
+        message: "response truncated before completion".into(),
+    })
+}
+
+fn fold_output(collected: &mut GenerationOutput, output: GenerationOutput) {
+    collected.text.push_str(&output.text);
+    collected.token_ids.extend(output.token_ids);
+    collected.prompt_tokens = output.prompt_tokens;
+    collected.completion_tokens = collected
+        .completion_tokens
+        .saturating_add(output.completion_tokens);
+    if output.finish_reason.is_some() {
+        collected.finish_reason = output.finish_reason;
+    }
+    if let Some(output) = output.extras {
+        let collected = collected
+            .extras
+            .get_or_insert_with(|| Box::new(crate::GenerationOutputExtras::default()));
+        collected.output_logprobs.extend(output.output_logprobs);
+        if !output.input_logprobs.is_empty() {
+            collected.input_logprobs = output.input_logprobs;
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use futures::{StreamExt, stream};
+
+    use super::super::test_utils::position;
+    use super::{fold_output, merge_indexed};
+    use crate::{GenerationOutput, GenerationOutputExtras};
+
+    #[test]
+    fn unary_output_appends_generated_logprobs_and_replaces_prompt_logprobs() {
+        let mut collected = GenerationOutput::default();
+        for (output_token, input_token) in [(1, 10), (2, 20)] {
+            fold_output(
+                &mut collected,
+                GenerationOutput {
+                    extras: Some(Box::new(GenerationOutputExtras {
+                        output_logprobs: vec![position(output_token, -0.1, &[])],
+                        input_logprobs: vec![position(input_token, -0.2, &[])],
+                    })),
+                    ..Default::default()
+                },
+            );
+        }
+        let extras = collected.extras.unwrap();
+        assert_eq!(extras.output_logprobs[0].token.token_id, 1);
+        assert_eq!(extras.output_logprobs[1].token.token_id, 2);
+        assert_eq!(extras.input_logprobs[0].token.token_id, 20);
+    }
+
+    #[tokio::test]
+    async fn merged_stream_preserves_choice_indexes() {
+        let choice0 = stream::iter([
+            Ok(GenerationOutput {
+                text: "a".into(),
+                ..Default::default()
+            }),
+            Ok(GenerationOutput {
+                text: "b".into(),
+                ..Default::default()
+            }),
+        ])
+        .boxed();
+        let choice1 = stream::iter([Ok(GenerationOutput {
+            text: "x".into(),
+            ..Default::default()
+        })])
+        .boxed();
+
+        let events = merge_indexed(vec![choice0, choice1])
+            .collect::<Vec<_>>()
+            .await;
+        let mut observed = events
+            .into_iter()
+            .map(|(index, event)| (index, event.unwrap().text))
+            .collect::<Vec<_>>();
+        observed.sort();
+        assert_eq!(
+            observed,
+            [(0, "a".into()), (0, "b".into()), (1, "x".into())]
+        );
+    }
+}

rust/sglang-renderer/src/engine/test_utils.rs

@@ -0,0 +1,31 @@
+use crate::{PositionLogprobs, TokenLogprob};
+
+fn logprob(token_id: i32, logprob: f32) -> TokenLogprob {
+    TokenLogprob {
+        logprob: Some(logprob),
+        token_id,
+        text: None,
+    }
+}
+
+pub(super) fn position(token_id: i32, value: f32, top: &[(i32, f32)]) -> PositionLogprobs {
+    PositionLogprobs {
+        token: logprob(token_id, value),
+        top: top
+            .iter()
+            .map(|&(token_id, logprob)| self::logprob(token_id, logprob))
+            .collect(),
+    }
+}
+
+pub(crate) fn tiny_tokenizer() -> dynamo_tokenizers::Tokenizer {
+    let path = std::path::Path::new(env!("CARGO_MANIFEST_DIR"))
+        .join("../../experimental/sgl-router/tests/fixtures/tiny_tokenizer.json");
+    dynamo_tokenizers::Tokenizer::from_file_with_options(
+        path.to_str().unwrap(),
+        dynamo_tokenizers::TokenizerOptions {
+            add_special_tokens: false,
+        },
+    )
+    .unwrap()
+}

rust/sglang-renderer/src/engine/tests.rs

@@ -0,0 +1,139 @@
+use std::sync::{
+    Arc, Mutex,
+    atomic::{AtomicUsize, Ordering},
+};
+
+use futures::{FutureExt, StreamExt, future::BoxFuture};
+
+use super::{
+    GenerateTransport, GenerationService, TokenDecoder, TokenDelta, TokenStream,
+    test_utils::{position, tiny_tokenizer},
+};
+use crate::{
+    GenerateRequest, GenerationFinishReason, GenerationOptions, GenerationOutputExtras,
+    MatchedStop, ResponseError, TokenIdsRequest,
+};
+
+struct DropNotice(Arc<AtomicUsize>);
+
+impl Drop for DropNotice {
+    fn drop(&mut self) {
+        self.0.fetch_add(1, Ordering::SeqCst);
+    }
+}
+
+struct MemoryTransport {
+    pending_submission: bool,
+    dropped: Arc<AtomicUsize>,
+    requests: Mutex<Vec<GenerateRequest>>,
+}
+
+impl GenerateTransport for MemoryTransport {
+    fn generate(
+        &self,
+        request: GenerateRequest,
+    ) -> BoxFuture<'_, Result<TokenStream, ResponseError>> {
+        Box::pin(async move {
+            let guard = DropNotice(self.dropped.clone());
+            self.requests.lock().unwrap().push(request);
+            if self.pending_submission {
+                futures::future::pending::<()>().await;
+            }
+            Ok(async_stream::stream! {
+                let _guard = guard;
+                for ids in [vec![104], vec![101, 108]] {
+                    yield Ok(TokenDelta {
+                        completion_tokens: ids.len() as u64,
+                        extras: Some(Box::new(GenerationOutputExtras {
+                            output_logprobs: ids.iter().map(|&id| position(id, -0.1, &[(id, -0.1)])).collect(),
+                            ..Default::default()
+                        })),
+                        token_ids: ids,
+                        prompt_tokens: 1,
+                        ..Default::default()
+                    });
+                }
+                futures::future::pending::<()>().await;
+            }.boxed())
+        })
+    }
+}
+
+fn transport(pending_submission: bool) -> Arc<MemoryTransport> {
+    Arc::new(MemoryTransport {
+        pending_submission,
+        dropped: Arc::new(AtomicUsize::new(0)),
+        requests: Mutex::new(Vec::new()),
+    })
+}
+
+fn request() -> GenerateRequest {
+    TokenIdsRequest {
+        rid: "generate".into(),
+        input_ids: vec![65],
+        options: GenerationOptions::default(),
+        metadata: Default::default(),
+    }
+    .into()
+}
+
+#[tokio::test]
+async fn shared_decoder_stops_across_chunks_and_releases_transport() {
+    for no_stop_trim in [false, true] {
+        let transport = transport(false);
+        let service =
+            GenerationService::new(transport.clone(), TokenDecoder::new(tiny_tokenizer()));
+        let mut request = request();
+        request.sampling_params.stop = vec!["he".into()];
+        request.sampling_params.stop_token_ids = Some(vec![9]);
+        request.sampling_params.no_stop_trim = no_stop_trim;
+        request.return_text_in_logprobs = Some(true);
+        let mut events = service.generate(request).await.unwrap();
+
+        let first = events.next().await.unwrap().unwrap();
+        assert!(first.text.is_empty());
+        let last = events.next().await.unwrap().unwrap();
+        assert_eq!(last.text, if no_stop_trim { "he" } else { "" });
+        assert_eq!(last.token_ids, [101]);
+        assert_eq!(last.completion_tokens, 1);
+        assert_eq!(
+            last.finish_reason,
+            Some(GenerationFinishReason::Stop(Some(MatchedStop::Text(
+                "he".into()
+            ))))
+        );
+        let positions = &last.extras.unwrap().output_logprobs;
+        assert_eq!(positions.len(), 1);
+        assert_eq!(positions[0].token.text.as_deref(), Some("e"));
+        assert_eq!(positions[0].top[0].text.as_deref(), Some("e"));
+        // Release upstream as soon as a local stop is emitted, even if the caller
+        // keeps the completed response stream alive without polling it again.
+        assert_eq!(transport.dropped.load(Ordering::SeqCst), 1);
+        assert!(events.next().await.is_none());
+
+        let sent = transport.requests.lock().unwrap();
+        assert_eq!(sent[0].sampling_params.stop, ["he"]);
+        assert_eq!(sent[0].sampling_params.stop_token_ids, Some(vec![9]));
+        assert_eq!(sent[0].return_text_in_logprobs, Some(false));
+    }
+}
+
+#[tokio::test]
+async fn cancellation_releases_pending_submissions_and_unpolled_streams() {
+    for pending_submission in [true, false] {
+        let transport = transport(pending_submission);
+        let service =
+            GenerationService::new(transport.clone(), TokenDecoder::new(tiny_tokenizer()));
+        let submission = service.generate_many(vec![request(), request(), request()]);
+        if pending_submission {
+            // Poll every submission once, then cancel the aggregate future.
+            assert!(submission.now_or_never().is_none());
+        } else {
+            let streams = submission.await.unwrap();
+            assert_eq!(transport.dropped.load(Ordering::SeqCst), 0);
+            drop(streams);
+        }
+        assert_eq!(transport.requests.lock().unwrap().len(), 3);
+        assert_eq!(transport.dropped.load(Ordering::SeqCst), 3);
+    }
+}

rust/sglang-renderer/src/engine/types.rs

@@ -0,0 +1,78 @@
+//! Generated output shared by the OpenAI response paths.
+
+use futures::stream::BoxStream;
+
+use crate::{ResponseError, TokenIds};
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum MatchedStop {
+    Token(i64),
+    Text(String),
+    Tokens(Vec<i64>),
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum GenerationFinishReason {
+    Stop(Option<MatchedStop>),
+    Length,
+    Abort,
+    ContentFilter,
+    Other(String),
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct TokenLogprob {
+    pub logprob: Option<f32>,
+    pub token_id: i32,
+    pub text: Option<String>,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct PositionLogprobs {
+    pub token: TokenLogprob,
+    pub top: Vec<TokenLogprob>,
+}
+
+#[derive(Debug, Clone, Default)]
+pub struct GenerationOutputExtras {
+    pub output_logprobs: Vec<PositionLogprobs>,
+    pub input_logprobs: Vec<PositionLogprobs>,
+}
+
+/// One decoded engine delta. All owned buffers are moved across the boundary.
+#[derive(Debug, Clone, Default)]
+pub struct GenerationOutput {
+    pub text: String,
+    pub token_ids: TokenIds,
+    pub finish_reason: Option<GenerationFinishReason>,
+    pub prompt_tokens: u32,
+    pub completion_tokens: u64,
+    pub extras: Option<Box<GenerationOutputExtras>>,
+}
+
+pub type GenerationStream = BoxStream<'static, Result<GenerationOutput, ResponseError>>;
+
+/// Normalized engine token delta, before renderer-owned text decoding.
+/// Completion counts are deltas; prompt counts describe the complete prompt.
+/// A successful stream includes a terminal finish reason.
+#[derive(Debug, Clone, Default)]
+pub(crate) struct TokenDelta {
+    pub token_ids: TokenIds,
+    pub finish_reason: Option<GenerationFinishReason>,
+    pub prompt_tokens: u32,
+    pub completion_tokens: u64,
+    pub extras: Option<Box<GenerationOutputExtras>>,
+}
+
+impl From<TokenDelta> for GenerationOutput {
+    fn from(delta: TokenDelta) -> Self {
+        Self {
+            text: String::new(),
+            token_ids: delta.token_ids,
+            finish_reason: delta.finish_reason,
+            prompt_tokens: delta.prompt_tokens,
+            completion_tokens: delta.completion_tokens,
+            extras: delta.extras,
+        }
+    }
+}

rust/sglang-renderer/src/error.rs

@@ -0,0 +1,89 @@
+//! Transport-neutral renderer failures.
+
+use serde::{Deserialize, Serialize};
+use thiserror::Error;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum RendererErrorKind {
+    InvalidRequest,
+    Tokenize,
+    Unavailable,
+    Internal,
+}
+
+#[derive(Debug, Clone, Error)]
+pub enum RendererError {
+    #[error("{0}")]
+    Request(String),
+    #[error("validation failed: {0}")]
+    Validation(String),
+    #[error("tokenize failed: {0}")]
+    Tokenize(String),
+    #[error("renderer is shutting down")]
+    Unavailable,
+    #[error("render preprocessing worker failed")]
+    WorkerDropped,
+    #[error("internal renderer error: {0}")]
+    Internal(String),
+}
+
+impl From<String> for RendererError {
+    fn from(message: String) -> Self {
+        Self::Request(message)
+    }
+}
+
+impl From<&str> for RendererError {
+    fn from(message: &str) -> Self {
+        Self::Request(message.to_owned())
+    }
+}
+
+impl RendererError {
+    pub fn kind(&self) -> RendererErrorKind {
+        match self {
+            Self::Request(_) | Self::Validation(_) => RendererErrorKind::InvalidRequest,
+            Self::Tokenize(_) => RendererErrorKind::Tokenize,
+            Self::Unavailable => RendererErrorKind::Unavailable,
+            Self::WorkerDropped | Self::Internal(_) => RendererErrorKind::Internal,
+        }
+    }
+}
+
+/// A host error carried through semantic processing without interpreting it.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ResponseError {
+    pub kind: ResponseErrorKind,
+    pub message: String,
+}
+
+impl From<RendererError> for ResponseError {
+    fn from(error: RendererError) -> Self {
+        let kind = match error.kind() {
+            RendererErrorKind::InvalidRequest => ResponseErrorKind::InvalidRequest,
+            RendererErrorKind::Unavailable => ResponseErrorKind::Unavailable,
+            RendererErrorKind::Tokenize | RendererErrorKind::Internal => {
+                ResponseErrorKind::Internal
+            }
+        };
+        ResponseError {
+            kind,
+            message: error.to_string(),
+        }
+    }
+}
+
+/// Failure category interpreted by the receiving transport adapter.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub enum ResponseErrorKind {
+    InvalidRequest,
+    Unavailable,
+    Internal,
+    Upstream(UpstreamErrorCode),
+}
+
+/// Original upstream code, preserved without imposing response transport policy.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub enum UpstreamErrorCode {
+    Http(u16),
+}

rust/sglang-renderer/src/frontend/http/chat.rs

@@ -0,0 +1,37 @@
+//! HTTP chat completion adapter.
+
+use super::{
+    ChatCompletionRequest,
+    error::{json_rejection_response, response_error},
+    response::sse_response,
+};
+use crate::openai::chat::serialize_chat_stream_response;
+use crate::openai::{OpenAIService, OperationResponse};
+use axum::{
+    Json, Router,
+    extract::{State, rejection::JsonRejection},
+    response::{IntoResponse, Response},
+    routing::post,
+};
+use std::sync::Arc;
+
+pub(super) fn routes() -> Router<Arc<OpenAIService>> {
+    Router::new().route("/v1/chat/completions", post(chat_completions))
+}
+
+async fn chat_completions(
+    State(state): State<Arc<OpenAIService>>,
+    body: Result<Json<ChatCompletionRequest>, JsonRejection>,
+) -> Response {
+    let request = match body {
+        Ok(Json(request)) => request,
+        Err(error) => return json_rejection_response(error),
+    };
+    match state.chat(request).await {
+        Ok(OperationResponse::Unary(response)) => Json(response).into_response(),
+        Ok(OperationResponse::Stream(chunks)) => {
+            sse_response(chunks, serialize_chat_stream_response)
+        }
+        Err(error) => response_error(error),
+    }
+}

rust/sglang-renderer/src/frontend/http/completions.rs

@@ -0,0 +1,36 @@
+//! HTTP completion adapter.
+
+use super::{
+    CompletionRequest,
+    error::{json_rejection_response, response_error},
+    response::sse_response,
+};
+use crate::openai::{OpenAIService, OperationResponse};
+use axum::{
+    Json, Router,
+    extract::{State, rejection::JsonRejection},
+    response::{IntoResponse, Response},
+    routing::post,
+};
+use std::sync::Arc;
+
+pub(super) fn routes() -> Router<Arc<OpenAIService>> {
+    Router::new().route("/v1/completions", post(completions))
+}
+
+async fn completions(
+    State(state): State<Arc<OpenAIService>>,
+    body: Result<Json<CompletionRequest>, JsonRejection>,
+) -> Response {
+    let request = match body {
+        Ok(Json(request)) => request,
+        Err(error) => return json_rejection_response(error),
+    };
+    match state.complete(request).await {
+        Ok(OperationResponse::Unary(response)) => Json(response).into_response(),
+        Ok(OperationResponse::Stream(chunks)) => sse_response(chunks, |chunk| {
+            serde_json::to_string(&chunk).expect("OpenAI response must serialize")
+        }),
+        Err(error) => response_error(error),
+    }
+}

rust/sglang-renderer/src/frontend/http/error.rs

@@ -0,0 +1,47 @@
+use axum::{
+    Json,
+    extract::rejection::JsonRejection,
+    http::StatusCode,
+    response::{IntoResponse, Response},
+};
+
+use crate::ResponseError;
+
+fn openai_error(code: StatusCode, message: impl Into<String>) -> Response {
+    (code, Json(error_payload(code, message))).into_response()
+}
+
+pub(super) fn json_rejection_response(rejection: JsonRejection) -> Response {
+    let status = if rejection.status() == StatusCode::PAYLOAD_TOO_LARGE {
+        StatusCode::PAYLOAD_TOO_LARGE
+    } else {
+        StatusCode::BAD_REQUEST
+    };
+    openai_error(status, rejection.body_text())
+}
+
+pub(super) fn response_error(error: ResponseError) -> Response {
+    let status = response_status(&error);
+    openai_error(status, error.message)
+}
+
+pub(super) fn response_status(error: &ResponseError) -> StatusCode {
+    use crate::{ResponseErrorKind, UpstreamErrorCode};
+    match error.kind {
+        ResponseErrorKind::InvalidRequest => StatusCode::BAD_REQUEST,
+        ResponseErrorKind::Unavailable => StatusCode::SERVICE_UNAVAILABLE,
+        ResponseErrorKind::Internal => StatusCode::INTERNAL_SERVER_ERROR,
+        ResponseErrorKind::Upstream(UpstreamErrorCode::Http(code)) => {
+            StatusCode::from_u16(code).unwrap_or(StatusCode::INTERNAL_SERVER_ERROR)
+        }
+    }
+}
+
+pub(super) fn error_payload(status: StatusCode, message: impl Into<String>) -> serde_json::Value {
+    let error_type = if status.is_server_error() {
+        "InternalServerError"
+    } else {
+        "BadRequestError"
+    };
+    crate::openai::error_payload(status.as_u16(), message, error_type)
+}

rust/sglang-renderer/src/frontend/http/mod.rs

@@ -0,0 +1,72 @@
+//! OpenAI HTTP frontend and render-only routes.
+
+use std::sync::Arc;
+
+use axum::Router;
+
+use crate::engine::HttpGenerateClient;
+use crate::openai::OpenAIService;
+
+mod chat;
+mod completions;
+mod error;
+mod proxy;
+mod render;
+mod response;
+mod tokenize;
+
+#[cfg(test)]
+mod tests;
+
+use crate::openai::protocol::{ChatCompletionRequest, CompletionRequest};
+
+const DEFAULT_REQUEST_BODY_LIMIT_BYTES: usize = 32 * 1024 * 1024;
+
+pub(crate) fn inference_routes(frontend: OpenAIService) -> Router<()> {
+    Router::new()
+        .merge(chat::routes())
+        .merge(completions::routes())
+        .with_state(Arc::new(frontend))
+}
+
+fn renderer_routes(renderer: Arc<crate::RendererService>) -> Router<()> {
+    render::routes(renderer.clone()).merge(tokenize::routes(renderer))
+}
+
+fn with_request_body_limit(routes: Router<()>) -> Router<()> {
+    // Limit JSON extraction without buffering or limiting raw proxy bodies.
+    routes.layer(axum::extract::DefaultBodyLimit::max(
+        DEFAULT_REQUEST_BODY_LIMIT_BYTES,
+    ))
+}
+
+pub(crate) fn standalone_routes(
+    frontend: OpenAIService,
+    health_client: HttpGenerateClient,
+) -> Router<()> {
+    let renderer = frontend.renderer.clone();
+    let routes = inference_routes(frontend).merge(renderer_routes(renderer));
+    let routes = routes.merge(render::engine_health_route(health_client));
+    with_request_body_limit(routes)
+}
+
+pub(crate) fn render_only_routes(renderer: Arc<crate::RendererService>) -> Router<()> {
+    let routes = renderer_routes(renderer).merge(render::health_route());
+    with_request_body_limit(routes)
+}
+
+pub(crate) fn hosted_routes(
+    frontend: OpenAIService,
+    upstream_url: String,
+) -> Result<Router<()>, String> {
+    let renderer = frontend.renderer.clone();
+    let proxy = proxy::RustServerProxy::new(upstream_url)?;
+    let routes = inference_routes(frontend)
+        .merge(renderer_routes(renderer))
+        .merge(render::readiness_route())
+        .fallback(move |request| {
+            let proxy = proxy.clone();
+            async move { proxy.forward(request).await }
+        });
+    Ok(with_request_body_limit(routes))
+}

rust/sglang-renderer/src/frontend/http/proxy.rs

@@ -0,0 +1,92 @@
+//! Streaming HTTP fallback to the native Rust server.
+
+use axum::body::Body;
+use axum::http::{HeaderMap, HeaderName, Request, Response, StatusCode, header};
+use axum::response::IntoResponse;
+
+#[derive(Clone)]
+pub(super) struct RustServerProxy {
+    client: reqwest::Client,
+    upstream_url: String,
+}
+
+impl RustServerProxy {
+    pub(super) fn new(upstream_url: String) -> Result<Self, String> {
+        let upstream_url = upstream_url.trim_end_matches('/').to_owned();
+        reqwest::Url::parse(&upstream_url)
+            .map_err(|error| format!("invalid proxy upstream {upstream_url:?}: {error}"))?;
+        let client = reqwest::Client::builder()
+            .redirect(reqwest::redirect::Policy::none())
+            .build()
+            .map_err(|error| format!("building Rust-server proxy client failed: {error}"))?;
+        Ok(Self {
+            client,
+            upstream_url,
+        })
+    }
+
+    pub(super) async fn forward(&self, request: Request<Body>) -> Response<Body> {
+        let (mut parts, body) = request.into_parts();
+        strip_hop_by_hop_headers(&mut parts.headers);
+        // Let the client set Host for the upstream origin.
+        parts.headers.remove(header::HOST);
+        let path = parts
+            .uri
+            .path_and_query()
+            .map_or("/", axum::http::uri::PathAndQuery::as_str);
+        let upstream = format!("{}{path}", self.upstream_url);
+        let response = self
+            .client
+            .request(parts.method, upstream)
+            .headers(parts.headers)
+            .body(reqwest::Body::wrap_stream(body.into_data_stream()))
+            .send()
+            .await;
+        let response = match response {
+            Ok(response) => response,
+            Err(error) => {
+                tracing::error!(%error, "Rust-server proxy request failed");
+                return (StatusCode::BAD_GATEWAY, "Rust server unavailable").into_response();
+            }
+        };
+
+        let status = response.status();
+        let mut headers = response.headers().clone();
+        strip_hop_by_hop_headers(&mut headers);
+        let mut builder = Response::builder().status(status);
+        *builder
+            .headers_mut()
+            .expect("response builder must expose headers") = headers;
+        builder
+            .body(Body::from_stream(response.bytes_stream()))
+            .unwrap_or_else(|error| {
+                tracing::error!(%error, "building Rust-server proxy response failed");
+                (StatusCode::BAD_GATEWAY, "Invalid Rust server response").into_response()
+            })
+    }
+}
+
+fn strip_hop_by_hop_headers(headers: &mut HeaderMap) {
+    let connection_headers = headers
+        .get(header::CONNECTION)
+        .and_then(|value| value.to_str().ok())
+        .into_iter()
+        .flat_map(|value| value.split(','))
+        .filter_map(|name| HeaderName::from_bytes(name.trim().as_bytes()).ok())
+        .collect::<Vec<_>>();
+    for name in connection_headers {
+        headers.remove(name);
+    }
+    for name in [
+        header::CONNECTION,
+        header::HeaderName::from_static("keep-alive"),
+        header::PROXY_AUTHENTICATE,
+        header::PROXY_AUTHORIZATION,
+        header::TE,
+        header::TRAILER,
+        header::TRANSFER_ENCODING,
+        header::UPGRADE,
+    ] {
+        headers.remove(name);
+    }
+}

rust/sglang-renderer/src/frontend/http/render.rs

@@ -0,0 +1,248 @@
+//! Render-only HTTP routes and renderer health endpoints.
+
+use super::{
+    ChatCompletionRequest, CompletionRequest,
+    error::{json_rejection_response, response_error},
+};
+use crate::{RendererService, engine::HttpGenerateClient};
+use axum::{
+    Json, Router,
+    extract::{State, rejection::JsonRejection},
+    http::StatusCode,
+    response::{IntoResponse, Response},
+    routing::{get, post},
+};
+use std::sync::Arc;
+
+pub(super) fn routes(renderer: Arc<RendererService>) -> Router<()> {
+    Router::new()
+        .route("/v1/chat/completions/render", post(render_chat))
+        .route("/v1/completions/render", post(render_completions))
+        .with_state(renderer)
+}
+
+pub(super) fn health_route() -> Router<()> {
+    Router::new().route("/health", get(health))
+}
+
+pub(super) fn engine_health_route(generate_client: HttpGenerateClient) -> Router<()> {
+    Router::new()
+        .route("/health", get(engine_health))
+        .with_state(generate_client)
+}
+
+pub(super) fn readiness_route() -> Router<()> {
+    Router::new().route("/_sglang_renderer/ready", get(readiness))
+}
+
+async fn health() -> StatusCode {
+    StatusCode::OK
+}
+
+async fn engine_health(State(generate_client): State<HttpGenerateClient>) -> StatusCode {
+    match generate_client.health_status().await {
+        Ok(status) => status,
+        Err(error) => {
+            tracing::warn!(message = %error.message, "engine health check failed");
+            StatusCode::SERVICE_UNAVAILABLE
+        }
+    }
+}
+
+async fn readiness() -> impl IntoResponse {
+    (StatusCode::NO_CONTENT, [("x-sglang-renderer", "ready")])
+}
+
+async fn render_chat(
+    State(renderer): State<Arc<RendererService>>,
+    body: Result<Json<ChatCompletionRequest>, JsonRejection>,
+) -> Response {
+    let request = match body {
+        Ok(Json(request)) => request,
+        Err(error) => return json_rejection_response(error),
+    };
+    match crate::openai::render::render_chat(&renderer, request).await {
+        Ok(request) => Json(request).into_response(),
+        Err(error) => response_error(error),
+    }
+}
+
+async fn render_completions(
+    State(renderer): State<Arc<RendererService>>,
+    body: Result<Json<CompletionRequest>, JsonRejection>,
+) -> Response {
+    let request = match body {
+        Ok(Json(request)) => request,
+        Err(error) => return json_rejection_response(error),
+    };
+    match crate::openai::render::render_completions(&renderer, request).await {
+        Ok(requests) => Json(requests).into_response(),
+        Err(error) => response_error(error),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use axum::{
+        body::{Body, to_bytes},
+        http::Request,
+    };
+    use tower::ServiceExt;
+
+    use crate::{RendererConfig, RendererError, RendererLimits, SamplingDefaults, TextTokenizer};
+
+    struct WordTokenizer;
+
+    impl TextTokenizer for WordTokenizer {
+        fn encode(&self, text: &str, _add_special_tokens: bool) -> Result<Vec<i32>, RendererError> {
+            Ok(text.split_whitespace().map(|_| 7).collect())
+        }
+    }
+
+    fn app() -> Router<()> {
+        let config = RendererConfig {
+            served_model_name: "model".into(),
+            tokenizer_path: ".".into(),
+            revision: None,
+            model_path: String::new(),
+            chat_template: Some("chatml".into()),
+            tool_call_parser: None,
+            reasoning_parser: None,
+            default_chat_template_kwargs: Default::default(),
+            stream_response_default_include_usage: false,
+            default_sampling_params: SamplingDefaults::default(),
+            limits: RendererLimits {
+                vocab_size: 100,
+                context_len: 64,
+                num_reserved_tokens: 0,
+                allow_auto_truncate: false,
+                enable_return_hidden_states: false,
+            },
+        };
+        routes(Arc::new(RendererService::with_tokenizer(
+            config,
+            Arc::new(WordTokenizer),
+            2,
+            2,
+        )))
+    }
+
+    #[tokio::test]
+    async fn completion_render_returns_token_only_generate_requests() {
+        let response = app()
+            .oneshot(
+                Request::builder()
+                    .method("POST")
+                    .uri("/v1/completions/render")
+                    .header("content-type", "application/json")
+                    .body(Body::from(
+                        serde_json::json!({
+                            "model": "model",
+                            "prompt": ["one two", "three"],
+                            "n": 2,
+                            "max_tokens": 5,
+                            "top_k": 17,
+                            "min_p": 0.2,
+                            "min_tokens": 3,
+                            "stop_regex": "END[0-9]",
+                            "rid": "request-id",
+                            "cache_salt": "tenant-a",
+                            "extra_key": "interactive",
+                            "priority": 7,
+                            "bootstrap_host": "prefill",
+                            "bootstrap_port": 8998,
+                            "bootstrap_room": 42,
+                            "routed_dp_rank": 2,
+                            "disagg_prefill_dp_rank": 1
+                        })
+                        .to_string(),
+                    ))
+                    .unwrap(),
+            )
+            .await
+            .unwrap();
+        assert_eq!(response.status(), StatusCode::OK);
+        let body: serde_json::Value =
+            serde_json::from_slice(&to_bytes(response.into_body(), 64 * 1024).await.unwrap())
+                .unwrap();
+        assert_eq!(body[0]["input_ids"], serde_json::json!([7, 7]));
+        assert_eq!(body[1]["input_ids"], serde_json::json!([7, 7]));
+        assert_eq!(body[2]["input_ids"], serde_json::json!([7]));
+        assert_eq!(body[3]["input_ids"], serde_json::json!([7]));
+        assert!(
+            body.as_array()
+                .unwrap()
+                .iter()
+                .all(|request| request.get("text").is_none())
+        );
+        assert_eq!(body[0]["sampling_params"]["top_k"], 17);
+        assert_eq!(body[0]["sampling_params"]["min_p"], 0.2);
+        assert_eq!(body[0]["sampling_params"]["min_new_tokens"], 3);
+        assert_eq!(
+            body[0]["sampling_params"]["stop_regex"],
+            serde_json::json!(["END[0-9]"])
+        );
+        assert_eq!(body[0]["rid"], "request-id-0");
+        assert_eq!(body[0]["model"], "model");
+        assert_eq!(body[0]["cache_salt"], "tenant-a");
+        assert_eq!(body[0]["extra_key"], "interactive");
+        assert_eq!(body[0]["priority"], 7);
+        assert_eq!(body[0]["bootstrap_host"], "prefill");
+        assert_eq!(body[0]["bootstrap_port"], 8998);
+        assert_eq!(body[0]["bootstrap_room"], 42);
+        assert_eq!(body[0]["routed_dp_rank"], 2);
+        assert_eq!(body[0]["disagg_prefill_dp_rank"], 1);
+        assert_eq!(body[1]["rid"], "request-id-1");
+        assert_eq!(body[2]["rid"], "request-id-2");
+        assert_eq!(body[3]["rid"], "request-id-3");
+        assert_eq!(body[3]["cache_salt"], "tenant-a");
+    }
+
+    #[tokio::test]
+    async fn chat_render_rejects_multiple_choices() {
+        let response = app()
+            .oneshot(
+                Request::builder()
+                    .method("POST")
+                    .uri("/v1/chat/completions/render")
+                    .header("content-type", "application/json")
+                    .body(Body::from(
+                        serde_json::json!({
+                            "model": "model",
+                            "messages": [{"role": "user", "content": "hello"}],
+                            "n": 2
+                        })
+                        .to_string(),
+                    ))
+                    .unwrap(),
+            )
+            .await
+            .unwrap();
+        assert_eq!(response.status(), StatusCode::BAD_REQUEST);
+    }
+
+    #[tokio::test]
+    async fn render_rejects_unimplemented_stateful_fields() {
+        let response = app()
+            .oneshot(
+                Request::builder()
+                    .method("POST")
+                    .uri("/v1/completions/render")
+                    .header("content-type", "application/json")
+                    .body(Body::from(
+                        serde_json::json!({
+                            "model": "model",
+                            "prompt": "hello",
+                            "session_id": "session"
+                        })
+                        .to_string(),
+                    ))
+                    .unwrap(),
+            )
+            .await
+            .unwrap();
+
+        assert_eq!(response.status(), StatusCode::BAD_REQUEST);
+    }
+}

rust/sglang-renderer/src/frontend/http/response.rs

@@ -0,0 +1,35 @@
+//! HTTP SSE framing for typed OpenAI response streams.
+
+use super::error::error_payload;
+use crate::ResponseError;
+use axum::response::{
+    IntoResponse, Response,
+    sse::{Event, Sse},
+};
+use futures::{Stream, StreamExt};
+use std::convert::Infallible;
+
+pub(super) fn sse_response<T, S, F>(chunks: S, serialize: F) -> Response
+where
+    T: Send + 'static,
+    S: Stream<Item = Result<T, ResponseError>> + Send + 'static,
+    F: Fn(T) -> String + Send + 'static,
+{
+    let events = async_stream::stream! {
+        futures::pin_mut!(chunks);
+        while let Some(chunk) = chunks.next().await {
+            let data = match chunk {
+                Ok(chunk) => serialize(chunk),
+                Err(error) => {
+                    let status = super::error::response_status(&error);
+                    error_payload(status, error.message).to_string()
+                }
+            };
+            yield Ok::<_, Infallible>(Event::default().data(data));
+        }
+        // An error may be followed by the protocol's final usage chunk.
+        // Only this transport owns the SSE terminator.
+        yield Ok::<_, Infallible>(Event::default().data("[DONE]"));
+    };
+    Sse::new(events).into_response()
+}

rust/sglang-renderer/src/frontend/http/tokenize.rs

@@ -0,0 +1,171 @@
+//! HTTP tokenization adapter.
+
+use super::error::{json_rejection_response, response_error};
+use crate::{
+    RendererService,
+    openai::tokenize::{TokenizeRequest, tokenize as tokenize_request},
+};
+use axum::{
+    Json, Router,
+    extract::{State, rejection::JsonRejection},
+    response::Response,
+    routing::post,
+};
+use serde_json::Value;
+use std::sync::Arc;
+
+pub(super) fn routes(renderer: Arc<RendererService>) -> Router<()> {
+    Router::new()
+        .route("/tokenize", post(tokenize))
+        .route("/v1/tokenize", post(tokenize))
+        .with_state(renderer)
+}
+
+async fn tokenize(
+    State(renderer): State<Arc<RendererService>>,
+    body: Result<Json<TokenizeRequest>, JsonRejection>,
+) -> Result<Json<Value>, Response> {
+    let Json(request) = body.map_err(json_rejection_response)?;
+    tokenize_request(&renderer, request)
+        .await
+        .map(Json)
+        .map_err(response_error)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use axum::{
+        body::{Body, to_bytes},
+        http::{Request, StatusCode},
+    };
+    use serde_json::json;
+    use tower::ServiceExt;
+
+    use crate::{RendererConfig, RendererError, RendererLimits, SamplingDefaults, TextTokenizer};
+
+    struct PrefixTokenizer;
+
+    impl TextTokenizer for PrefixTokenizer {
+        fn encode(&self, text: &str, add_special_tokens: bool) -> Result<Vec<i32>, RendererError> {
+            Ok(add_special_tokens
+                .then_some(1)
+                .into_iter()
+                .chain(text.split_whitespace().map(|_| 7))
+                .chain(add_special_tokens.then_some(2))
+                .collect())
+        }
+    }
+
+    fn app() -> Router<()> {
+        let config = RendererConfig {
+            served_model_name: "model".into(),
+            tokenizer_path: ".".into(),
+            revision: None,
+            model_path: String::new(),
+            chat_template: Some("chatml".into()),
+            tool_call_parser: None,
+            reasoning_parser: None,
+            default_chat_template_kwargs: Default::default(),
+            stream_response_default_include_usage: false,
+            default_sampling_params: SamplingDefaults::default(),
+            limits: RendererLimits {
+                vocab_size: 100,
+                context_len: 64,
+                num_reserved_tokens: 0,
+                allow_auto_truncate: false,
+                enable_return_hidden_states: false,
+            },
+        };
+        routes(Arc::new(RendererService::with_tokenizer(
+            config,
+            Arc::new(PrefixTokenizer),
+            2,
+            2,
+        )))
+    }
+
+    async fn post(body: Value) -> (StatusCode, Value) {
+        let response = app()
+            .oneshot(
+                Request::builder()
+                    .method("POST")
+                    .uri("/v1/tokenize")
+                    .header("content-type", "application/json")
+                    .body(Body::from(body.to_string()))
+                    .unwrap(),
+            )
+            .await
+            .unwrap();
+        let status = response.status();
+        let body =
+            serde_json::from_slice(&to_bytes(response.into_body(), 64 * 1024).await.unwrap())
+                .unwrap();
+        (status, body)
+    }
+
+    #[tokio::test]
+    async fn prompt_tokenization_preserves_batch_shape_and_special_token_choice() {
+        let (status, body) = post(json!({
+            "prompt": ["one two", ""],
+            "add_special_tokens": false
+        }))
+        .await;
+        assert_eq!(status, StatusCode::OK);
+        assert_eq!(body["tokens"], json!([[7, 7], []]));
+        assert_eq!(body["count"], json!([2, 0]));
+
+        let (_, body) = post(json!({"prompt": "one"})).await;
+        assert_eq!(body["tokens"], json!([1, 7, 2]));
+    }
+
+    #[tokio::test]
+    async fn chat_tokenization_applies_the_template_without_generation_limits() {
+        let (status, body) = post(json!({
+            "messages": [{"role": "user", "content": "hello"}],
+            "max_completion_tokens": 10_000
+        }))
+        .await;
+        assert_eq!(status, StatusCode::OK);
+        assert!(
+            body["tokens"]
+                .as_array()
+                .is_some_and(|tokens| !tokens.is_empty())
+        );
+        assert_ne!(body["tokens"][0], json!(1));
+        assert_ne!(
+            body["tokens"][body["tokens"].as_array().unwrap().len() - 1],
+            json!(2)
+        );
+        assert_eq!(
+            body["count"],
+            json!(body["tokens"].as_array().unwrap().len())
+        );
+    }
+
+    #[tokio::test]
+    async fn chat_tokenization_continues_the_final_assistant_message() {
+        let (_, regular) = post(json!({
+            "messages": [
+                {"role": "user", "content": "hello"},
+                {"role": "assistant", "content": "partial answer"}
+            ]
+        }))
+        .await;
+        let (status, continued) = post(json!({
+            "messages": [
+                {"role": "user", "content": "hello"},
+                {"role": "assistant", "content": "partial answer"}
+            ],
+            "continue_final_message": true,
+            "chat_template_kwargs": {
+                "continue_final_message": false,
+                "add_generation_prompt": true
+            }
+        }))
+        .await;
+
+        assert_eq!(status, StatusCode::OK);
+        assert!(continued["count"].as_u64().unwrap() < regular["count"].as_u64().unwrap());
+    }
+}

rust/sglang-renderer/src/frontend/mod.rs

@@ -0,0 +1,4 @@
+//! Inbound protocol adapters.
+
+#[cfg(feature = "http")]
+pub(crate) mod http;

rust/sglang-renderer/src/launcher.rs

@@ -0,0 +1,720 @@
+//! Process launch configuration for the standalone renderer.
+
+use std::collections::{BTreeSet, HashMap};
+use std::net::{IpAddr, Ipv4Addr, SocketAddr};
+use std::path::{Path, PathBuf};
+
+use clap::{Parser, ValueEnum};
+use hf_hub::api::tokio::{ApiBuilder, ApiRepo};
+use hf_hub::{Cache, Repo, RepoType};
+use serde_json::Value;
+
+use crate::preprocessing::{resolve_model_file, resolve_tokenizer_file};
+use crate::{RendererConfig, RendererLimits, RendererRuntimeConfig, SamplingDefaults, serve};
+
+const DEFAULT_CONTEXT_LEN: u64 = 2048;
+
+#[derive(Debug, Parser)]
+#[command(
+    name = "sglang-renderer",
+    about = "Run the SGLang Rust renderer with an optional SGLang engine"
+)]
+struct Cli {
+    /// Model directory, config file, or Hugging Face repository id.
+    #[arg(value_name = "MODEL")]
+    model: String,
+
+    /// Optional SGLang engine origin exposing /generate.
+    ///
+    /// When omitted, only rendering and tokenization routes are served.
+    #[arg(long, value_name = "URL")]
+    engine_url: Option<String>,
+
+    /// Proxy routes not owned by the renderer to the SGLang engine origin.
+    #[arg(long, requires = "engine_url")]
+    proxy_unhandled_routes: bool,
+
+    #[arg(long)]
+    tokenizer_path: Option<String>,
+    #[arg(long)]
+    revision: Option<String>,
+    #[arg(long)]
+    served_model_name: Option<String>,
+    #[arg(long, default_value_t = IpAddr::V4(Ipv4Addr::LOCALHOST))]
+    host: IpAddr,
+    #[arg(long, default_value_t = 30000)]
+    port: u16,
+    #[arg(long, default_value_t = 2)]
+    http_workers: usize,
+    #[arg(long, default_value_t = 1)]
+    tokenizer_workers: usize,
+    #[arg(long, default_value_t = 128)]
+    queue_capacity: usize,
+    #[arg(long)]
+    chat_template: Option<String>,
+    #[arg(long)]
+    tool_call_parser: Option<String>,
+    #[arg(long)]
+    reasoning_parser: Option<String>,
+    #[arg(long, value_parser = parse_json_object)]
+    default_chat_template_kwargs: Option<HashMap<String, Value>>,
+    #[arg(long, value_enum, default_value_t)]
+    sampling_defaults: SamplingDefaultsSource,
+    /// Already-resolved sampling defaults. When set with context length and
+    /// vocabulary size, model metadata is not reopened by this process.
+    #[arg(long, value_parser = parse_sampling_defaults)]
+    resolved_sampling_params: Option<SamplingDefaults>,
+    #[arg(long)]
+    context_length: Option<u64>,
+    #[arg(long)]
+    vocab_size: Option<u64>,
+    #[arg(long, default_value_t = 0)]
+    num_reserved_tokens: u64,
+    #[arg(long)]
+    allow_auto_truncate: bool,
+    #[arg(long)]
+    enable_return_hidden_states: bool,
+    #[arg(long)]
+    stream_response_default_include_usage: bool,
+}
+
+#[derive(Clone, Copy, Debug, Default, Eq, PartialEq, ValueEnum)]
+enum SamplingDefaultsSource {
+    #[default]
+    Model,
+    Openai,
+}
+
+#[derive(Debug)]
+struct DirectArgs {
+    model: String,
+    engine_url: Option<String>,
+    proxy_unhandled_routes: bool,
+    tokenizer_path: String,
+    revision: Option<String>,
+    served_model_name: String,
+    http_addr: SocketAddr,
+    http_workers: usize,
+    tokenizer_workers: usize,
+    queue_capacity: usize,
+    chat_template: Option<String>,
+    tool_call_parser: Option<String>,
+    reasoning_parser: Option<String>,
+    default_chat_template_kwargs: HashMap<String, Value>,
+    sampling_defaults: SamplingDefaultsSource,
+    resolved_sampling_params: Option<SamplingDefaults>,
+    context_length: Option<u64>,
+    vocab_size: Option<u64>,
+    num_reserved_tokens: u64,
+    allow_auto_truncate: bool,
+    enable_return_hidden_states: bool,
+    stream_response_default_include_usage: bool,
+}
+
+pub fn run_cli() -> Result<(), String> {
+    let args = Cli::parse().into_direct_args();
+    let http_workers = args.http_workers;
+
+    tracing_subscriber::fmt()
+        .with_env_filter(
+            tracing_subscriber::EnvFilter::try_from_default_env().unwrap_or_else(|_| "info".into()),
+        )
+        .init();
+
+    let runtime = tokio::runtime::Builder::new_multi_thread()
+        .worker_threads(http_workers.max(1))
+        .enable_all()
+        .build()
+        .map_err(|error| format!("building renderer runtime failed: {error}"))?;
+    runtime.block_on(async { serve(args.resolve().await?).await })
+}
+
+impl Cli {
+    fn into_direct_args(self) -> DirectArgs {
+        let model = self.model;
+        let tokenizer_path = self.tokenizer_path.unwrap_or_else(|| model.clone());
+        let served_model_name = self.served_model_name.unwrap_or_else(|| model.clone());
+        let http_addr = SocketAddr::new(self.host, self.port);
+        DirectArgs {
+            model,
+            engine_url: self.engine_url,
+            proxy_unhandled_routes: self.proxy_unhandled_routes,
+            tokenizer_path,
+            revision: self.revision,
+            served_model_name,
+            http_addr,
+            http_workers: self.http_workers,
+            tokenizer_workers: self.tokenizer_workers,
+            queue_capacity: self.queue_capacity,
+            chat_template: self.chat_template,
+            tool_call_parser: self.tool_call_parser,
+            reasoning_parser: self.reasoning_parser,
+            default_chat_template_kwargs: self.default_chat_template_kwargs.unwrap_or_default(),
+            sampling_defaults: self.sampling_defaults,
+            resolved_sampling_params: self.resolved_sampling_params,
+            context_length: self.context_length,
+            vocab_size: self.vocab_size,
+            num_reserved_tokens: self.num_reserved_tokens,
+            allow_auto_truncate: self.allow_auto_truncate,
+            enable_return_hidden_states: self.enable_return_hidden_states,
+            stream_response_default_include_usage: self.stream_response_default_include_usage,
+        }
+    }
+}
+
+impl DirectArgs {
+    async fn resolve(self) -> Result<RendererRuntimeConfig, String> {
+        let (context_len, vocab_size, default_sampling_params) = match self.resolved_sampling_params
+        {
+            Some(default_sampling_params) => {
+                let context_len = self.context_length.ok_or_else(|| {
+                    "--resolved-sampling-params requires --context-length".to_string()
+                })?;
+                let vocab_size = self.vocab_size.ok_or_else(|| {
+                    "--resolved-sampling-params requires --vocab-size".to_string()
+                })?;
+                (context_len, vocab_size, default_sampling_params)
+            }
+            None => {
+                let files = resolve_required_files(
+                    &self.model,
+                    &self.tokenizer_path,
+                    self.revision.as_deref(),
+                )
+                .await?;
+                let model_config = read_json(&files.config_path)?;
+                let derived_context_len = derive_context_len(&model_config)?;
+                let context_len = match self.context_length {
+                    Some(context_len)
+                        if context_len > derived_context_len && !allow_longer_context() =>
+                    {
+                        return Err(format!(
+                            "user-specified context length {context_len} exceeds the model-derived context length {derived_context_len}; set SGLANG_ALLOW_OVERWRITE_LONGER_CONTEXT_LEN=1 to allow it"
+                        ));
+                    }
+                    Some(context_len) => context_len,
+                    None => derived_context_len,
+                };
+                let vocab_size = self
+                    .vocab_size
+                    .or_else(|| derive_vocab_size(&model_config))
+                    .ok_or_else(|| {
+                        "model config does not define vocab_size; pass --vocab-size explicitly"
+                            .to_string()
+                    })?;
+                let default_sampling_params = match self.sampling_defaults {
+                    SamplingDefaultsSource::Openai => SamplingDefaults::default(),
+                    SamplingDefaultsSource::Model => files
+                        .generation_config_path
+                        .as_deref()
+                        .map(read_sampling_defaults)
+                        .transpose()?
+                        .unwrap_or_default(),
+                };
+                (context_len, vocab_size, default_sampling_params)
+            }
+        };
+
+        Ok(RendererRuntimeConfig {
+            http_addr: self.http_addr,
+            http_workers: self.http_workers,
+            tokenizer_workers: self.tokenizer_workers,
+            queue_capacity: self.queue_capacity,
+            engine_url: self.engine_url,
+            proxy_unhandled_routes: self.proxy_unhandled_routes,
+            renderer: RendererConfig {
+                served_model_name: self.served_model_name,
+                tokenizer_path: self.tokenizer_path,
+                revision: self.revision,
+                model_path: self.model,
+                chat_template: self.chat_template,
+                tool_call_parser: self.tool_call_parser,
+                reasoning_parser: self.reasoning_parser,
+                default_chat_template_kwargs: self.default_chat_template_kwargs,
+                stream_response_default_include_usage: self.stream_response_default_include_usage,
+                default_sampling_params,
+                limits: RendererLimits {
+                    vocab_size,
+                    context_len,
+                    num_reserved_tokens: self.num_reserved_tokens,
+                    allow_auto_truncate: self.allow_auto_truncate,
+                    enable_return_hidden_states: self.enable_return_hidden_states,
+                },
+            },
+        })
+    }
+}
+
+#[derive(Debug)]
+struct ResolvedFiles {
+    config_path: PathBuf,
+    generation_config_path: Option<PathBuf>,
+}
+
+async fn resolve_required_files(
+    model: &str,
+    tokenizer: &str,
+    revision: Option<&str>,
+) -> Result<ResolvedFiles, String> {
+    let model_is_local = Path::new(model).exists();
+    let tokenizer_is_local = Path::new(tokenizer).exists();
+    let mut config_path = resolve_model_file(model, revision, "config.json").map(PathBuf::from);
+    let mut tokenizer_ready = resolve_tokenizer_file(tokenizer, revision).is_some();
+
+    if model_is_local && config_path.is_none() {
+        return Err(format!(
+            "local model source {model:?} does not contain config.json"
+        ));
+    }
+    if tokenizer_is_local && !tokenizer_ready {
+        return Err(format!(
+            "local tokenizer source {tokenizer:?} does not contain tokenizer.json, tiktoken.model, or *.tiktoken"
+        ));
+    }
+
+    let need_model = config_path.is_none();
+    let need_tokenizer = !tokenizer_ready;
+    if need_model || need_tokenizer {
+        if offline_mode() {
+            return Err(format!(
+                "required renderer metadata is not cached for model {model:?} and tokenizer {tokenizer:?}, and HF_HUB_OFFLINE is enabled"
+            ));
+        }
+        if model == tokenizer {
+            download_repository(model, revision, need_model, need_tokenizer).await?;
+        } else {
+            if need_model {
+                download_repository(model, revision, true, false).await?;
+            }
+            if need_tokenizer {
+                download_repository(tokenizer, revision, false, true).await?;
+            }
+        }
+        config_path = resolve_model_file(model, revision, "config.json").map(PathBuf::from);
+        tokenizer_ready = resolve_tokenizer_file(tokenizer, revision).is_some();
+    }
+
+    let config_path = config_path.ok_or_else(|| {
+        format!(
+            "model {model:?} does not expose config.json at revision {:?}",
+            revision.unwrap_or("main")
+        )
+    })?;
+    if !tokenizer_ready {
+        return Err(format!(
+            "tokenizer {tokenizer:?} does not expose tokenizer.json, tiktoken.model, or *.tiktoken at revision {:?}",
+            revision.unwrap_or("main")
+        ));
+    }
+    let generation_config_path =
+        resolve_model_file(model, revision, "generation_config.json").map(PathBuf::from);
+    Ok(ResolvedFiles {
+        config_path,
+        generation_config_path,
+    })
+}
+
+async fn download_repository(
+    repo_id: &str,
+    revision: Option<&str>,
+    include_model_metadata: bool,
+    include_tokenizer: bool,
+) -> Result<(), String> {
+    let mut builder = ApiBuilder::from_env()
+        .with_cache_dir(hf_cache().path().clone())
+        .with_progress(false);
+    if let Ok(token) = std::env::var("HF_TOKEN")
+        && !token.is_empty()
+    {
+        builder = builder.with_token(Some(token));
+    }
+    let api = builder
+        .build()
+        .map_err(|error| format!("building Hugging Face client failed: {error}"))?;
+    let repo = api.repo(Repo::with_revision(
+        repo_id.to_string(),
+        RepoType::Model,
+        revision.unwrap_or("main").to_string(),
+    ));
+    let info = repo.info().await.map_err(|error| {
+        format!(
+            "fetching Hugging Face metadata for {repo_id:?} at revision {:?} failed: {error}",
+            revision.unwrap_or("main")
+        )
+    })?;
+    let siblings = info
+        .siblings
+        .into_iter()
+        .map(|sibling| sibling.rfilename)
+        .collect::<BTreeSet<_>>();
+
+    if include_model_metadata {
+        if !siblings.contains("config.json") {
+            return Err(format!(
+                "Hugging Face model {repo_id:?} does not contain config.json"
+            ));
+        }
+        download_file(&repo, repo_id, "config.json").await?;
+        if siblings.contains("generation_config.json") {
+            download_file(&repo, repo_id, "generation_config.json").await?;
+        }
+    }
+    if include_tokenizer {
+        for filename in ["tokenizer_config.json", "config.json"] {
+            if siblings.contains(filename) {
+                download_file(&repo, repo_id, filename).await?;
+            }
+        }
+        let mut tokenizer_names = Vec::new();
+        if siblings.contains("tokenizer.json") {
+            tokenizer_names.push("tokenizer.json");
+        }
+        if siblings.contains("tiktoken.model") {
+            tokenizer_names.push("tiktoken.model");
+        } else if let Some(name) = siblings.iter().find(|name| name.ends_with(".tiktoken")) {
+            tokenizer_names.push(name);
+        }
+        if tokenizer_names.is_empty() {
+            return Err(format!(
+                "Hugging Face model {repo_id:?} does not contain tokenizer.json, tiktoken.model, or *.tiktoken"
+            ));
+        }
+        for tokenizer_name in tokenizer_names {
+            download_file(&repo, repo_id, tokenizer_name).await?;
+        }
+        let template_name = ["chat_template.json", "chat_template.jinja"]
+            .into_iter()
+            .find(|name| siblings.contains(*name))
+            .or_else(|| {
+                siblings
+                    .iter()
+                    .find(|name| name.ends_with(".jinja"))
+                    .map(String::as_str)
+            });
+        if let Some(template_name) = template_name {
+            download_file(&repo, repo_id, template_name).await?;
+        }
+    }
+    Ok(())
+}
+
+async fn download_file(repo: &ApiRepo, repo_id: &str, filename: &str) -> Result<PathBuf, String> {
+    repo.get(filename).await.map_err(|error| {
+        format!("downloading {filename:?} for Hugging Face model {repo_id:?} failed: {error}")
+    })
+}
+
+fn hf_cache() -> Cache {
+    ["HF_HUB_CACHE", "HUGGINGFACE_HUB_CACHE"]
+        .iter()
+        .find_map(|name| std::env::var(name).ok())
+        .map(PathBuf::from)
+        .map(Cache::new)
+        .unwrap_or_else(Cache::from_env)
+}
+
+fn read_json(path: &Path) -> Result<Value, String> {
+    let contents = std::fs::read_to_string(path)
+        .map_err(|error| format!("reading {} failed: {error}", path.display()))?;
+    serde_json::from_str(&contents)
+        .map_err(|error| format!("parsing {} failed: {error}", path.display()))
+}
+
+fn read_sampling_defaults(path: &Path) -> Result<SamplingDefaults, String> {
+    let value = read_json(path)?;
+    serde_json::from_value(value).map_err(|error| {
+        format!(
+            "parsing sampling defaults from {} failed: {error}",
+            path.display()
+        )
+    })
+}
+
+fn derive_context_len(config: &Value) -> Result<u64, String> {
+    let text = effective_text_config(config);
+    let factor = inherited_value(text, config, "rope_scaling")
+        .and_then(Value::as_object)
+        .map(|rope| {
+            if rope.contains_key("original_max_position_embeddings")
+                || rope.get("rope_type").and_then(Value::as_str) == Some("llama3")
+            {
+                1.0
+            } else {
+                rope.get("factor").and_then(Value::as_f64).unwrap_or(1.0)
+            }
+        })
+        .unwrap_or(1.0);
+    for key in [
+        "max_sequence_length",
+        "seq_length",
+        "max_seq_len",
+        "model_max_length",
+        "max_position_embeddings",
+    ] {
+        if let Some(value) = inherited_value(text, config, key).and_then(Value::as_u64) {
+            let scaled = factor * value as f64;
+            if !scaled.is_finite() || scaled <= 0.0 || scaled > u64::MAX as f64 {
+                return Err(format!(
+                    "invalid context length {value} with rope scaling factor {factor}"
+                ));
+            }
+            return Ok(scaled as u64);
+        }
+    }
+    Ok(DEFAULT_CONTEXT_LEN)
+}
+
+fn derive_vocab_size(config: &Value) -> Option<u64> {
+    let text = effective_text_config(config);
+    let architecture = config
+        .get("architectures")
+        .and_then(Value::as_array)
+        .and_then(|architectures| architectures.first())
+        .and_then(Value::as_str);
+    let key = if architecture == Some("GlmImageForConditionalGeneration") {
+        "vision_vocab_size"
+    } else {
+        "vocab_size"
+    };
+    inherited_value(text, config, key).and_then(Value::as_u64)
+}
+
+fn effective_text_config(config: &Value) -> &Value {
+    let is_non_hf_llava = config
+        .get("architectures")
+        .and_then(Value::as_array)
+        .and_then(|architectures| architectures.first())
+        .and_then(Value::as_str)
+        .is_some_and(|architecture| {
+            architecture.starts_with("Llava") && architecture.ends_with("ForCausalLM")
+        });
+    if is_non_hf_llava {
+        return config;
+    }
+    if let Some(thinker) = config.get("thinker_config") {
+        return thinker.get("text_config").unwrap_or(thinker);
+    }
+    for key in ["llm_config", "language_config", "text_config"] {
+        if let Some(text) = config.get(key) {
+            return text;
+        }
+    }
+    config
+}
+
+fn inherited_value<'a>(text: &'a Value, root: &'a Value, key: &str) -> Option<&'a Value> {
+    text.get(key).or_else(|| root.get(key))
+}
+
+fn parse_json_object(value: &str) -> Result<HashMap<String, Value>, String> {
+    serde_json::from_str(value).map_err(|error| format!("expected a JSON object: {error}"))
+}
+
+fn parse_sampling_defaults(value: &str) -> Result<SamplingDefaults, String> {
+    serde_json::from_str(value)
+        .map_err(|error| format!("expected resolved sampling parameters as JSON: {error}"))
+}
+
+fn offline_mode() -> bool {
+    std::env::var("HF_HUB_OFFLINE").ok().is_some_and(|value| {
+        matches!(
+            value.to_ascii_lowercase().as_str(),
+            "1" | "true" | "yes" | "on"
+        )
+    })
+}
+
+fn allow_longer_context() -> bool {
+    std::env::var("SGLANG_ALLOW_OVERWRITE_LONGER_CONTEXT_LEN")
+        .ok()
+        .is_some_and(|value| {
+            matches!(
+                value.to_ascii_lowercase().as_str(),
+                "1" | "true" | "yes" | "on"
+            )
+        })
+}
+
+#[cfg(test)]
+mod tests {
+    use std::fs;
+
+    use serde_json::json;
+
+    use super::*;
+
+    fn direct_cli(model: &Path) -> Cli {
+        Cli::try_parse_from(["sglang-renderer", model.to_str().unwrap()]).unwrap()
+    }
+
+    fn fixture_model(config: Value, generation_config: Option<Value>) -> PathBuf {
+        let directory =
+            std::env::temp_dir().join(format!("sglang-renderer-{}", uuid::Uuid::new_v4()));
+        fs::create_dir(&directory).unwrap();
+        fs::write(directory.join("config.json"), config.to_string()).unwrap();
+        fs::write(directory.join("tokenizer.json"), "{}").unwrap();
+        if let Some(generation_config) = generation_config {
+            fs::write(
+                directory.join("generation_config.json"),
+                generation_config.to_string(),
+            )
+            .unwrap();
+        }
+        directory
+    }
+
+    #[test]
+    fn cli_uses_sglang_renderer_defaults() {
+        let directory = fixture_model(
+            json!({"vocab_size": 128, "max_position_embeddings": 4096}),
+            None,
+        );
+        let args = direct_cli(&directory).into_direct_args();
+
+        assert_eq!(args.served_model_name, directory.to_string_lossy());
+        assert_eq!(args.tokenizer_path, directory.to_string_lossy());
+        assert_eq!(args.http_addr, "127.0.0.1:30000".parse().unwrap());
+        assert_eq!(args.http_workers, 2);
+        assert_eq!(args.tokenizer_workers, 1);
+        assert_eq!(args.queue_capacity, 128);
+        assert_eq!(args.engine_url, None);
+        assert_eq!(args.sampling_defaults, SamplingDefaultsSource::Model);
+        assert_eq!(args.resolved_sampling_params, None);
+        fs::remove_dir_all(directory).unwrap();
+    }
+
+    #[test]
+    fn proxying_unhandled_routes_requires_an_engine_url() {
+        let error = Cli::try_parse_from(["sglang-renderer", "model", "--proxy-unhandled-routes"])
+            .unwrap_err();
+
+        assert_eq!(
+            error.kind(),
+            clap::error::ErrorKind::MissingRequiredArgument
+        );
+    }
+
+    #[tokio::test]
+    async fn direct_resolution_matches_model_metadata_and_cli_overrides() {
+        let directory = fixture_model(
+            json!({
+                "vocab_size": 10,
+                "max_position_embeddings": 8192,
+                "thinker_config": {
+                    "text_config": {
+                        "vocab_size": 128,
+                        "max_position_embeddings": 4096,
+                        "rope_scaling": {"factor": 2.0}
+                    }
+                }
+            }),
+            Some(json!({
+                "temperature": 0.7,
+                "top_p": 0.9,
+                "top_k": 20,
+                "min_p": 0.1,
+                "repetition_penalty": 1.05,
+                "max_new_tokens": 32
+            })),
+        );
+        let cli = Cli::try_parse_from([
+            "sglang-renderer",
+            directory.to_str().unwrap(),
+            "--engine-url",
+            "http://127.0.0.1:30001",
+            "--proxy-unhandled-routes",
+            "--served-model-name",
+            "fixture",
+            "--context-length",
+            "2048",
+            "--vocab-size",
+            "256",
+            "--num-reserved-tokens",
+            "8",
+            "--default-chat-template-kwargs",
+            r#"{"enable_thinking":false}"#,
+        ])
+        .unwrap();
+        let config = cli.into_direct_args().resolve().await.unwrap();
+
+        assert_eq!(config.engine_url.as_deref(), Some("http://127.0.0.1:30001"));
+        assert!(config.proxy_unhandled_routes);
+        assert_eq!(config.renderer.served_model_name, "fixture");
+        assert_eq!(config.renderer.limits.context_len, 2048);
+        assert_eq!(config.renderer.limits.vocab_size, 256);
+        assert_eq!(config.renderer.limits.num_reserved_tokens, 8);
+        assert_eq!(config.renderer.default_sampling_params.top_k, Some(20));
+        assert_eq!(config.renderer.default_sampling_params.min_p, Some(0.1));
+        assert_eq!(
+            config.renderer.default_chat_template_kwargs,
+            HashMap::from([("enable_thinking".to_string(), json!(false))])
+        );
+        fs::remove_dir_all(directory).unwrap();
+    }
+
+    #[tokio::test]
+    async fn resolved_metadata_does_not_reopen_a_gguf_model_source() {
+        let directory =
+            std::env::temp_dir().join(format!("sglang-renderer-{}", uuid::Uuid::new_v4()));
+        let tokenizer = directory.join("tokenizer");
+        let model = directory.join("model.gguf");
+        fs::create_dir_all(&tokenizer).unwrap();
+        fs::write(tokenizer.join("tokenizer.json"), "{}").unwrap();
+        fs::write(&model, "not needed by the renderer").unwrap();
+
+        let cli = Cli::try_parse_from([
+            "sglang-renderer",
+            model.to_str().unwrap(),
+            "--engine-url",
+            "http://127.0.0.1:30001",
+            "--tokenizer-path",
+            tokenizer.to_str().unwrap(),
+            "--context-length",
+            "4096",
+            "--vocab-size",
+            "128",
+            "--resolved-sampling-params",
+            r#"{"temperature":0.7,"top_k":20}"#,
+        ])
+        .unwrap();
+        let config = cli.into_direct_args().resolve().await.unwrap();
+
+        assert_eq!(config.renderer.model_path, model.to_string_lossy());
+        assert_eq!(config.renderer.limits.context_len, 4096);
+        assert_eq!(config.renderer.limits.vocab_size, 128);
+        assert_eq!(
+            config.renderer.default_sampling_params,
+            SamplingDefaults {
+                temperature: Some(0.7),
+                top_k: Some(20),
+                ..SamplingDefaults::default()
+            }
+        );
+        fs::remove_dir_all(directory).unwrap();
+    }
+
+    #[test]
+    fn context_derivation_matches_python_key_and_rope_precedence() {
+        assert_eq!(
+            derive_context_len(&json!({
+                "seq_length": 1000,
+                "max_position_embeddings": 2000,
+                "rope_scaling": {"factor": 4.0}
+            }))
+            .unwrap(),
+            4000
+        );
+        assert_eq!(
+            derive_context_len(&json!({
+                "max_position_embeddings": 2000,
+                "rope_scaling": {
+                    "factor": 4.0,
+                    "original_max_position_embeddings": 2000
+                }
+            }))
+            .unwrap(),
+            2000
+        );
+        assert_eq!(derive_context_len(&json!({})).unwrap(), 2048);
+    }
+}

rust/sglang-renderer/src/lib.rs

@@ -0,0 +1,52 @@
+//! Reusable request preprocessing for SGLang.
+//!
+//! The core renders normalized chat requests, lowers textual completions,
+//! tokenizes prompts, and produces the token-in contract consumed by SGLang.
+//! OpenAI operations and generation decoding are independent of transport.
+//! The optional `http` feature adds HTTP adapters, the SGLang HTTP engine client,
+//! and the process runtime. Protocol adapters own middleware and framing;
+//! shared services own request preparation, submission policy, and decoding.
+
+mod config;
+// Shared serving code is compiled without HTTP; production adapters are optional.
+#[cfg_attr(not(feature = "http"), allow(dead_code))]
+mod engine;
+mod error;
+mod frontend;
+#[cfg(feature = "http")]
+mod launcher;
+#[cfg_attr(not(feature = "http"), allow(dead_code))]
+mod openai;
+mod postprocessing;
+mod preprocessing;
+#[cfg(feature = "http")]
+mod runtime;
+mod types;
+
+pub use config::{RendererConfig, RendererLimits, SamplingDefaults};
+pub(crate) use engine::{
+    GenerationFinishReason, GenerationOutput, GenerationOutputExtras, GenerationStream,
+    MatchedStop, PositionLogprobs, TokenLogprob,
+};
+pub use error::{
+    RendererError, RendererErrorKind, ResponseError, ResponseErrorKind, UpstreamErrorCode,
+};
+#[cfg(feature = "http")]
+pub use launcher::run_cli;
+pub use postprocessing::{
+    ChatEvent, ChatFinishReason, ChatResponseProcessor, ChatToolCallDelta, DecodedChatEvent,
+};
+pub(crate) use preprocessing::ChatFormatter;
+pub(crate) use preprocessing::SamplingParamsOverrides;
+pub(crate) use preprocessing::{ChatPreprocessor, LoweredChat};
+pub use preprocessing::{
+    ChatRequest, DynamoTokenizer, PreparedChat, ReasoningEffort, RendererService, SamplingParams,
+    TextTokenizer, load_tokenizer,
+};
+pub use preprocessing::{
+    GenerateRequest, GenerateRequestMetadata, GenerateSamplingParams, GenerationOptions,
+    TextRequest, TokenIdsRequest,
+};
+#[cfg(feature = "http")]
+pub use runtime::{RendererRuntimeConfig, serve};
+pub use types::{OneOrMany, TokenIds};

rust/sglang-renderer/src/main.rs

@@ -0,0 +1,8 @@
+fn main() {
+    sglang_renderer::run_cli().unwrap_or_else(|error| exit(error));
+}
+
+fn exit(message: impl std::fmt::Display) -> ! {
+    eprintln!("sglang-renderer: {message}");
+    std::process::exit(2)
+}

rust/sglang-renderer/src/openai/chat.rs

@@ -0,0 +1,917 @@
+//! OpenAI chat preparation, response aggregation, and typed chunks.
+
+use std::collections::BTreeMap;
+
+use crate::{
+    ChatEvent, ChatFinishReason, ChatResponseProcessor, ChatToolCallDelta, DecodedChatEvent,
+    GenerationFinishReason, GenerationOutput, GenerationOutputExtras, GenerationStream,
+    ResponseError,
+};
+use dynamo_protocols::types::{
+    ChatChoice, ChatChoiceLogprobs, ChatChoiceStream, ChatCompletionMessageContent,
+    ChatCompletionMessageToolCall, ChatCompletionMessageToolCallChunk,
+    ChatCompletionResponseMessage, ChatCompletionStreamResponseDelta,
+    ChatCompletionStreamResponseDeltaFunctionCall, ChatCompletionTokenLogprob, CompletionUsage,
+    CreateChatCompletionResponse, CreateChatCompletionStreamResponse,
+    FinishReason as OpenAIFinishReason, FunctionCall, FunctionCallStream, FunctionType, Role,
+    ServiceTier as ChatServiceTier, TopLogprobs,
+};
+use futures::StreamExt;
+use serde::Serialize;
+
+use super::protocol::{ChatCompletionRequest, lower_chat_request};
+use super::{completion_usage, unix_seconds_u32};
+use crate::engine::response::merge_indexed;
+
+pub(crate) struct ChatResponseContext {
+    pub(crate) response_id: String,
+    pub(crate) model: String,
+    pub(crate) created: u32,
+    pub(crate) want_logprobs: bool,
+    pub(crate) include_usage: bool,
+    pub(crate) service_tier: Option<ChatServiceTier>,
+}
+
+pub(crate) async fn prepare_request(
+    renderer: &crate::RendererService,
+    request: ChatCompletionRequest,
+) -> Result<(String, crate::PreparedChat), ResponseError> {
+    let (response_id, request) = lower_chat_request(renderer.config(), request)?;
+    let chat = renderer.prepare_chat(request).await?;
+    Ok((response_id, chat))
+}
+
+#[allow(clippy::too_many_arguments)]
+pub(crate) async fn unary_chat(
+    submitted: Vec<(usize, GenerationStream)>,
+    response_processor: ChatResponseProcessor,
+    response_id: String,
+    model: String,
+    created: u32,
+    want_logprobs: bool,
+    service_tier: Option<ChatServiceTier>,
+) -> Result<CreateChatCompletionResponse, ResponseError> {
+    let choice_count = submitted.len();
+    let mut accumulated = (0..choice_count)
+        .map(|_| UnaryChatChoice::default())
+        .collect::<Vec<_>>();
+    let mut prompt_tokens = 0u32;
+    let mut completion_tokens = 0u64;
+    let parsed = semantic_chat_stream(submitted, response_processor, want_logprobs);
+    futures::pin_mut!(parsed);
+    while let Some(item) = parsed.next().await {
+        match item {
+            Ok(ChatEvent::Role { .. }) => {}
+            Ok(ChatEvent::Delta {
+                choice,
+                content,
+                reasoning_content,
+                tool_calls,
+                finish_reason,
+                logprobs,
+            }) => {
+                let Some(choice) = accumulated.get_mut(choice) else {
+                    return Err(ResponseError {
+                        kind: crate::ResponseErrorKind::Internal,
+                        message: "chat response choice is out of range".into(),
+                    });
+                };
+                if let Some(content) = content {
+                    choice.content.push_str(&content);
+                }
+                if let Some(reasoning) = reasoning_content {
+                    choice.reasoning_content.push_str(&reasoning);
+                }
+                if let Some(tool_calls) = tool_calls {
+                    choice.extend_tool_calls(tool_calls);
+                }
+                if finish_reason.is_some() {
+                    choice.finish_reason = finish_reason;
+                }
+                merge_chat_logprobs(&mut choice.logprobs, logprobs);
+            }
+            Ok(ChatEvent::Usage {
+                prompt_tokens: prompt,
+                completion_tokens: completion,
+            }) => {
+                prompt_tokens = prompt;
+                completion_tokens = completion;
+            }
+            Err(error) => {
+                return Err(error);
+            }
+        }
+    }
+
+    let choices = accumulated
+        .into_iter()
+        .enumerate()
+        .map(|(index, parsed)| {
+            #[allow(deprecated)]
+            let message = ChatCompletionResponseMessage {
+                content: (!parsed.content.is_empty())
+                    .then_some(ChatCompletionMessageContent::Text(parsed.content)),
+                refusal: None,
+                tool_calls: (!parsed.tool_calls.is_empty()).then(|| {
+                    parsed
+                        .tool_calls
+                        .into_values()
+                        .map(|call| ChatCompletionMessageToolCall {
+                            id: call.id,
+                            r#type: FunctionType::Function,
+                            function: FunctionCall {
+                                name: call.name,
+                                arguments: call.arguments,
+                            },
+                        })
+                        .collect()
+                }),
+                role: Role::Assistant,
+                function_call: None,
+                audio: None,
+                // Python: `reasoning_text if reasoning_text else None`.
+                reasoning_content: (!parsed.reasoning_content.is_empty())
+                    .then_some(parsed.reasoning_content),
+            };
+            ChatChoice {
+                index: u32::try_from(index).unwrap_or(u32::MAX),
+                message,
+                finish_reason: parsed.finish_reason.map(openai_finish_reason),
+                logprobs: parsed.logprobs,
+            }
+        })
+        .collect();
+
+    Ok(CreateChatCompletionResponse {
+        id: response_id,
+        choices,
+        created,
+        model,
+        service_tier,
+        system_fingerprint: None,
+        object: "chat.completion".into(),
+        usage: Some(completion_usage(
+            prompt_tokens,
+            u32::try_from(completion_tokens).unwrap_or(u32::MAX),
+        )),
+    })
+}
+
+#[derive(Default)]
+struct UnaryChatChoice {
+    content: String,
+    reasoning_content: String,
+    tool_calls: BTreeMap<u32, UnaryToolCall>,
+    finish_reason: Option<ChatFinishReason>,
+    logprobs: Option<ChatChoiceLogprobs>,
+}
+
+#[derive(Default)]
+struct UnaryToolCall {
+    id: String,
+    name: String,
+    arguments: String,
+}
+
+impl UnaryChatChoice {
+    fn extend_tool_calls(&mut self, deltas: Vec<ChatToolCallDelta>) {
+        for delta in deltas {
+            let call = self.tool_calls.entry(delta.index).or_default();
+            if let Some(id) = delta.id {
+                call.id = id;
+            }
+            if let Some(name) = delta.name {
+                call.name = name;
+            }
+            if let Some(arguments) = delta.arguments {
+                call.arguments.push_str(&arguments);
+            }
+        }
+    }
+}
+
+fn merge_chat_logprobs(
+    collected: &mut Option<ChatChoiceLogprobs>,
+    delta: Option<ChatChoiceLogprobs>,
+) {
+    let Some(mut delta) = delta else {
+        return;
+    };
+    let collected = collected.get_or_insert_with(|| ChatChoiceLogprobs {
+        content: Some(Vec::new()),
+        refusal: None,
+    });
+    if let Some(content) = delta.content.take() {
+        collected
+            .content
+            .get_or_insert_with(Vec::new)
+            .extend(content);
+    }
+}
+
+pub(crate) fn chat_event_stream(
+    submitted: Vec<(usize, GenerationStream)>,
+    response_processor: ChatResponseProcessor,
+    context: ChatResponseContext,
+) -> impl futures::Stream<Item = Result<CreateChatCompletionStreamResponse, ResponseError>> {
+    let parsed = semantic_chat_stream(submitted, response_processor, context.want_logprobs);
+
+    async_stream::stream! {
+        futures::pin_mut!(parsed);
+        while let Some(item) = parsed.next().await {
+            match item {
+                Ok(ChatEvent::Role { choice }) => {
+                    yield Ok(chat_stream_response(
+                        &context.response_id,
+                        &context.model,
+                        context.created,
+                        context.service_tier.clone(),
+                        vec![ChatChoiceStream {
+                            index: choice as u32,
+                            delta: chat_delta(None, Some(Role::Assistant), None, None),
+                            finish_reason: None,
+                            logprobs: None,
+                        }],
+                        None,
+                    ));
+                }
+                Ok(ChatEvent::Delta {
+                    choice,
+                    content,
+                    reasoning_content,
+                    tool_calls,
+                    finish_reason,
+                    logprobs,
+                }) => {
+                    yield Ok(chat_stream_response(
+                        &context.response_id,
+                        &context.model,
+                        context.created,
+                        context.service_tier.clone(),
+                        vec![ChatChoiceStream {
+                            index: choice as u32,
+                            delta: chat_delta(
+                                content,
+                                None,
+                                tool_calls.map(|calls| {
+                                    calls.into_iter().map(openai_tool_call_delta).collect()
+                                }),
+                                reasoning_content,
+                            ),
+                            finish_reason: finish_reason.map(openai_finish_reason),
+                            logprobs,
+                        }],
+                        None,
+                    ));
+                }
+                Ok(ChatEvent::Usage {
+                    prompt_tokens,
+                    completion_tokens,
+                }) if context.include_usage => {
+                    yield Ok(chat_stream_response(
+                        &context.response_id,
+                        &context.model,
+                        context.created,
+                        context.service_tier.clone(),
+                        Vec::new(),
+                        Some((prompt_tokens, completion_tokens)),
+                    ));
+                }
+                Ok(ChatEvent::Usage { .. }) => {}
+                Err(error) => {
+                    yield Err(error);
+                }
+            }
+        }
+    }
+}
+
+fn semantic_chat_stream(
+    submitted: Vec<(usize, GenerationStream)>,
+    response_processor: ChatResponseProcessor,
+    want_logprobs: bool,
+) -> impl futures::Stream<Item = Result<ChatEvent, ResponseError>> {
+    let raw = async_stream::stream! {
+        let streams = submitted.into_iter().map(|(_, events)| events).collect();
+        let mut events = merge_indexed(streams);
+        while let Some((index, item)) = events.next().await {
+            let output = match item {
+                Ok(output) => output,
+                Err(error) => {
+                    yield Err(error);
+                    break;
+                }
+            };
+            let finish_reason = chat_finish_reason(&output);
+            let logprobs = want_logprobs.then(|| chat_logprobs(output.extras.as_deref()));
+            yield Ok(DecodedChatEvent {
+                choice: index,
+                text: output.text,
+                token_ids: output.token_ids,
+                finish_reason,
+                logprobs,
+                prompt_tokens: output.prompt_tokens,
+                completion_tokens: output.completion_tokens,
+            });
+        }
+    };
+    response_processor.process_stream(raw)
+}
+
+fn chat_finish_reason(output: &GenerationOutput) -> Option<ChatFinishReason> {
+    output.finish_reason.as_ref().map(|reason| match reason {
+        GenerationFinishReason::Length => ChatFinishReason::Length,
+        GenerationFinishReason::ContentFilter => ChatFinishReason::ContentFilter,
+        GenerationFinishReason::Stop(_)
+        | GenerationFinishReason::Abort
+        | GenerationFinishReason::Other(_) => ChatFinishReason::Stop,
+    })
+}
+
+#[allow(deprecated)]
+fn chat_logprobs(extras: Option<&GenerationOutputExtras>) -> ChatChoiceLogprobs {
+    let mut content = Vec::new();
+    let Some(extras) = extras else {
+        return ChatChoiceLogprobs {
+            content: Some(content),
+            refusal: None,
+        };
+    };
+    for position in &extras.output_logprobs {
+        let selected = &position.token;
+        let token = selected
+            .text
+            .clone()
+            .unwrap_or_else(|| format!("token_id:{}", selected.token_id));
+        let top_logprobs = position
+            .top
+            .iter()
+            .map(|candidate| {
+                let text = candidate
+                    .text
+                    .clone()
+                    .unwrap_or_else(|| format!("token_id:{}", candidate.token_id));
+                TopLogprobs {
+                    bytes: Some(text.as_bytes().to_vec()),
+                    token: text,
+                    logprob: candidate.logprob.unwrap_or(f32::NAN),
+                }
+            })
+            .collect();
+        content.push(ChatCompletionTokenLogprob {
+            bytes: Some(token.as_bytes().to_vec()),
+            token,
+            logprob: selected.logprob.unwrap_or(f32::NAN),
+            token_id: u32::try_from(selected.token_id).ok(),
+            top_logprobs,
+        });
+    }
+    ChatChoiceLogprobs {
+        content: Some(content),
+        refusal: None,
+    }
+}
+
+#[allow(deprecated)]
+fn chat_delta(
+    content: Option<String>,
+    role: Option<Role>,
+    tool_calls: Option<Vec<ChatCompletionMessageToolCallChunk>>,
+    reasoning_content: Option<String>,
+) -> ChatCompletionStreamResponseDelta {
+    ChatCompletionStreamResponseDelta {
+        content: content.map(ChatCompletionMessageContent::Text),
+        function_call: None,
+        tool_calls,
+        role,
+        refusal: None,
+        reasoning_content,
+    }
+}
+
+fn chat_stream_response(
+    response_id: &str,
+    model: &str,
+    created: u32,
+    service_tier: Option<ChatServiceTier>,
+    choices: Vec<ChatChoiceStream>,
+    usage: Option<(u32, u64)>,
+) -> CreateChatCompletionStreamResponse {
+    CreateChatCompletionStreamResponse {
+        id: response_id.to_owned(),
+        choices,
+        created,
+        model: model.to_owned(),
+        service_tier,
+        system_fingerprint: None,
+        object: "chat.completion.chunk".into(),
+        usage: usage.map(|(prompt, completion)| {
+            completion_usage(prompt, u32::try_from(completion).unwrap_or(u32::MAX))
+        }),
+    }
+}
+
+fn openai_finish_reason(reason: ChatFinishReason) -> OpenAIFinishReason {
+    match reason {
+        ChatFinishReason::Stop => OpenAIFinishReason::Stop,
+        ChatFinishReason::Length => OpenAIFinishReason::Length,
+        ChatFinishReason::ContentFilter => OpenAIFinishReason::ContentFilter,
+        ChatFinishReason::ToolCalls => OpenAIFinishReason::ToolCalls,
+    }
+}
+
+fn openai_tool_call_delta(call: ChatToolCallDelta) -> ChatCompletionMessageToolCallChunk {
+    ChatCompletionMessageToolCallChunk {
+        index: call.index,
+        id: call.id,
+        r#type: Some(FunctionType::Function),
+        function: Some(FunctionCallStream {
+            name: call.name,
+            arguments: call.arguments,
+        }),
+    }
+}
+
+pub(crate) fn serialize_chat_stream_response(
+    response: CreateChatCompletionStreamResponse,
+) -> String {
+    serde_json::to_string(&ChatStreamResponseWire::from(&response))
+        .expect("OpenAI response must serialize")
+}
+
+/// The Dynamo response type omits an absent `reasoning_content`. SGLang's
+/// streaming contract emits it explicitly as `null`, so use a borrowed wire
+/// view instead of building and patching a `serde_json::Value` tree.
+#[derive(Serialize)]
+struct ChatStreamResponseWire<'a> {
+    id: &'a str,
+    choices: Vec<ChatChoiceStreamWire<'a>>,
+    created: u32,
+    model: &'a str,
+    service_tier: &'a Option<ChatServiceTier>,
+    system_fingerprint: &'a Option<String>,
+    object: &'a str,
+    usage: &'a Option<CompletionUsage>,
+}
+
+impl<'a> From<&'a CreateChatCompletionStreamResponse> for ChatStreamResponseWire<'a> {
+    fn from(response: &'a CreateChatCompletionStreamResponse) -> Self {
+        Self {
+            id: &response.id,
+            choices: response
+                .choices
+                .iter()
+                .map(ChatChoiceStreamWire::from)
+                .collect(),
+            created: response.created,
+            model: &response.model,
+            service_tier: &response.service_tier,
+            system_fingerprint: &response.system_fingerprint,
+            object: &response.object,
+            usage: &response.usage,
+        }
+    }
+}
+
+#[derive(Serialize)]
+struct ChatChoiceStreamWire<'a> {
+    index: u32,
+    delta: ChatDeltaWire<'a>,
+    finish_reason: &'a Option<OpenAIFinishReason>,
+    logprobs: &'a Option<ChatChoiceLogprobs>,
+}
+
+impl<'a> From<&'a ChatChoiceStream> for ChatChoiceStreamWire<'a> {
+    fn from(choice: &'a ChatChoiceStream) -> Self {
+        Self {
+            index: choice.index,
+            delta: ChatDeltaWire::from(&choice.delta),
+            finish_reason: &choice.finish_reason,
+            logprobs: &choice.logprobs,
+        }
+    }
+}
+
+#[derive(Serialize)]
+struct ChatDeltaWire<'a> {
+    #[serde(skip_serializing_if = "Option::is_none")]
+    content: Option<&'a ChatCompletionMessageContent>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    function_call: Option<&'a ChatCompletionStreamResponseDeltaFunctionCall>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    tool_calls: Option<&'a Vec<ChatCompletionMessageToolCallChunk>>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    role: Option<&'a Role>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    refusal: Option<&'a String>,
+    reasoning_content: Option<&'a str>,
+}
+
+impl<'a> From<&'a ChatCompletionStreamResponseDelta> for ChatDeltaWire<'a> {
+    fn from(delta: &'a ChatCompletionStreamResponseDelta) -> Self {
+        Self {
+            content: delta.content.as_ref(),
+            function_call: delta.function_call.as_ref(),
+            tool_calls: delta.tool_calls.as_ref(),
+            role: delta.role.as_ref(),
+            refusal: delta.refusal.as_ref(),
+            reasoning_content: delta.reasoning_content.as_deref(),
+        }
+    }
+}
+
+impl super::OpenAIService {
+    pub(crate) async fn chat(
+        &self,
+        request: ChatCompletionRequest,
+    ) -> Result<
+        super::OperationResponse<CreateChatCompletionResponse, CreateChatCompletionStreamResponse>,
+        ResponseError,
+    > {
+        use super::OperationResponse;
+        let stream = request.stream.unwrap_or(false);
+        let model = request.model.clone();
+        let want_logprobs = request.logprobs.unwrap_or(false);
+        let include_usage = request
+            .stream_options
+            .as_ref()
+            .is_some_and(|options| options.include_usage)
+            || self.renderer.config().stream_response_default_include_usage;
+        let service_tier = request.service_tier.clone();
+        let (response_id, chat) = prepare_request(&self.renderer, request).await?;
+        let context = ChatResponseContext {
+            response_id,
+            model,
+            created: unix_seconds_u32(),
+            want_logprobs,
+            include_usage,
+            service_tier,
+        };
+        let streams = match self.generation.generate_many(chat.requests).await {
+            Ok(streams) => streams,
+            Err(error) if stream => {
+                return Ok(OperationResponse::Stream(
+                    futures::stream::once(async { Err(error) }).boxed(),
+                ));
+            }
+            Err(error) => return Err(error),
+        };
+        let submitted = streams.into_iter().enumerate().collect();
+        if stream {
+            Ok(OperationResponse::Stream(
+                chat_event_stream(submitted, chat.response_processor, context).boxed(),
+            ))
+        } else {
+            unary_chat(
+                submitted,
+                chat.response_processor,
+                context.response_id,
+                context.model,
+                context.created,
+                context.want_logprobs,
+                context.service_tier,
+            )
+            .await
+            .map(OperationResponse::Unary)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{ChatResponseContext, chat_event_stream, chat_logprobs, unary_chat};
+    use crate::openai::protocol::ChatCompletionRequest;
+    use crate::openai::protocol::{chat_sampling_params, lower_chat_request};
+    use crate::openai::test_utils::{chat_submitted, chunk};
+    use crate::{
+        ChatPreprocessor, GenerationOutputExtras, PositionLogprobs, RendererConfig, RendererLimits,
+        ResponseError, SamplingDefaults, TokenLogprob,
+    };
+    use futures::{FutureExt, StreamExt};
+
+    fn request() -> ChatCompletionRequest {
+        serde_json::from_value(serde_json::json!({
+            "model": "test",
+            "messages": [{"role": "user", "content": "hi"}]
+        }))
+        .unwrap()
+    }
+
+    fn response_processor(
+        reasoning_parser: Option<&str>,
+        choices: usize,
+    ) -> crate::ChatResponseProcessor {
+        let config = RendererConfig {
+            model_path: String::new(),
+            served_model_name: "model".into(),
+            tokenizer_path: ".".into(),
+            chat_template: Some("chatml".into()),
+            tool_call_parser: None,
+            reasoning_parser: reasoning_parser.map(str::to_owned),
+            default_chat_template_kwargs: Default::default(),
+            revision: None,
+            stream_response_default_include_usage: false,
+            default_sampling_params: SamplingDefaults::default(),
+            limits: RendererLimits {
+                vocab_size: 128,
+                context_len: 128,
+                num_reserved_tokens: 0,
+                allow_auto_truncate: false,
+                enable_return_hidden_states: false,
+            },
+        };
+        let request: ChatCompletionRequest = serde_json::from_value(serde_json::json!({
+            "model": "model",
+            "messages": [{"role": "user", "content": "hi"}],
+            "n": choices
+        }))
+        .unwrap();
+        let (_, chat) = lower_chat_request(&config, request).unwrap();
+        ChatPreprocessor::new(
+            &config,
+            Some(crate::preprocessing::load_test_chat_formatter("chatml")),
+        )
+        .preprocess(chat)
+        .unwrap()
+        .response_processor
+    }
+
+    fn wire_context(include_usage: bool) -> ChatResponseContext {
+        ChatResponseContext {
+            response_id: "chatcmpl-test".into(),
+            model: "model".into(),
+            created: 1,
+            want_logprobs: false,
+            include_usage,
+            service_tier: None,
+        }
+    }
+
+    /// Python `to_sampling_params` priority: user value > model generation
+    /// config (`--sampling-defaults model`) > OpenAI terminal default.
+    #[test]
+    fn sampling_defaults_follow_python_priority_chain() {
+        let model = SamplingDefaults {
+            temperature: Some(0.6),
+            top_p: Some(0.9),
+            top_k: Some(32),
+            min_p: Some(0.1),
+            repetition_penalty: Some(1.1),
+        };
+        // Omitted → model defaults, not the 1.0 OpenAI terminals.
+        let sampling = chat_sampling_params(&request(), &model).unwrap();
+        assert_eq!(sampling.temperature, 0.6);
+        assert_eq!(sampling.top_p, 0.9);
+        assert_eq!(sampling.top_k, 32);
+        assert_eq!(sampling.min_p, 0.1);
+        assert_eq!(sampling.repetition_penalty, 1.1);
+        // Explicit request values win. `Option<f32>` loses precision in f64 —
+        // compare with tolerance.
+        let mut request = request();
+        request.temperature = Some(0.2);
+        request.top_p = Some(0.5);
+        let sampling = chat_sampling_params(&request, &model).unwrap();
+        assert!((sampling.temperature - 0.2).abs() < 1e-6);
+        assert!((sampling.top_p - 0.5).abs() < 1e-6);
+    }
+
+    /// `--sampling-defaults openai` resolves an empty model-config slice, so the
+    /// conversion falls back to the OpenAI terminal defaults.
+    #[test]
+    fn sampling_defaults_fall_back_to_openai_terminals_in_openai_mode() {
+        let openai_mode = SamplingDefaults::default();
+        let sampling = chat_sampling_params(&request(), &openai_mode).unwrap();
+        assert_eq!(sampling.temperature, 1.0);
+        assert_eq!(sampling.top_p, 1.0);
+        assert_eq!(sampling.top_k, 1 << 30);
+        assert_eq!(sampling.min_p, 0.0);
+        assert_eq!(sampling.repetition_penalty, 1.0);
+    }
+
+    /// A request with no `max_tokens`/`max_completion_tokens` stays unbounded —
+    /// no terminal default is imposed.
+    #[test]
+    fn chat_without_a_token_limit_stays_unbounded() {
+        let request: ChatCompletionRequest = serde_json::from_value(serde_json::json!({
+            "model": "test",
+            "messages": [{"role": "user", "content": "hello"}]
+        }))
+        .unwrap();
+        assert_eq!(
+            chat_sampling_params(&request, &SamplingDefaults::default())
+                .unwrap()
+                .max_new_tokens,
+            None
+        );
+    }
+
+    #[test]
+    fn chat_logprobs_use_dynamo_wire_types() {
+        let extras = GenerationOutputExtras {
+            output_logprobs: vec![PositionLogprobs {
+                token: TokenLogprob {
+                    logprob: Some(-0.25),
+                    token_id: 7,
+                    text: Some("x".into()),
+                },
+                top: vec![
+                    TokenLogprob {
+                        logprob: Some(-0.25),
+                        token_id: 7,
+                        text: Some("x".into()),
+                    },
+                    TokenLogprob {
+                        logprob: Some(-1.0),
+                        token_id: 8,
+                        text: Some("y".into()),
+                    },
+                ],
+            }],
+            ..Default::default()
+        };
+        let logprobs = chat_logprobs(Some(&extras));
+        let token = &logprobs.content.unwrap()[0];
+        assert_eq!(token.token, "x");
+        assert_eq!(token.token_id, Some(7));
+        assert_eq!(token.top_logprobs.len(), 2);
+        assert_eq!(token.top_logprobs[1].token, "y");
+    }
+
+    #[tokio::test]
+    async fn unary_chat_fans_in_choices_and_usage() {
+        let (choice0, tx0) = chat_submitted(0);
+        let (choice1, tx1) = chat_submitted(1);
+        tx0.send(chunk("Paris", true)).await.unwrap();
+        tx1.send(chunk("Paris", true)).await.unwrap();
+
+        let response = unary_chat(
+            vec![choice0, choice1],
+            response_processor(None, 2),
+            "chatcmpl-test".into(),
+            "model".into(),
+            1,
+            false,
+            None,
+        )
+        .await;
+        let value = serde_json::to_value(response.unwrap()).unwrap();
+        assert_eq!(value["choices"][0]["message"]["role"], "assistant");
+        assert_eq!(value["choices"][0]["message"]["content"], "Paris");
+        assert_eq!(value["choices"][1]["index"], 1);
+        assert_eq!(value["usage"]["prompt_tokens"], 5);
+        assert_eq!(value["usage"]["completion_tokens"], 2);
+    }
+
+    #[tokio::test]
+    async fn unary_chat_separates_reasoning_content_with_parser_configured() {
+        let (choice, tx) = chat_submitted(0);
+        tx.send(chunk("<think>because Paris is famous</think>Paris", true))
+            .await
+            .unwrap();
+
+        let response = unary_chat(
+            vec![choice],
+            response_processor(Some("deepseek-r1"), 1),
+            "chatcmpl-test".into(),
+            "model".into(),
+            1,
+            false,
+            None,
+        )
+        .await;
+        let value = serde_json::to_value(response.unwrap()).unwrap();
+        assert_eq!(
+            value["choices"][0]["message"]["reasoning_content"],
+            "because Paris is famous"
+        );
+        assert_eq!(value["choices"][0]["message"]["content"], "Paris");
+        assert!(value["choices"][0]["message"]["reasoning_content"].is_string());
+    }
+
+    #[tokio::test]
+    async fn streaming_chat_separates_reasoning_into_own_deltas() {
+        let (choice, tx) = chat_submitted(0);
+        // Force mode starts in reasoning, so the opener is stripped and the first
+        // reasoning fragment streams immediately.
+        tx.send(chunk("<think>be", false)).await.unwrap();
+        tx.send(chunk("cause</think>Par", false)).await.unwrap();
+        tx.send(chunk("is", true)).await.unwrap();
+
+        let stream = chat_event_stream(
+            vec![choice],
+            response_processor(Some("deepseek-r1"), 1),
+            wire_context(true),
+        );
+        futures::pin_mut!(stream);
+        let frames: Vec<_> = stream
+            .map(|chunk| serde_json::to_value(chunk.unwrap()).unwrap())
+            .collect()
+            .await;
+        let role = &frames[0];
+        let first_reasoning = &frames[1];
+        let second_reasoning = &frames[2];
+        let content = &frames[3];
+        let terminal = &frames[4];
+        assert_eq!(role["choices"][0]["delta"]["role"], "assistant");
+        assert_eq!(
+            first_reasoning["choices"][0]["delta"]["reasoning_content"],
+            "be"
+        );
+        assert!(first_reasoning["choices"][0]["delta"]["content"].is_null());
+        assert_eq!(
+            second_reasoning["choices"][0]["delta"]["reasoning_content"],
+            "cause"
+        );
+        assert_eq!(content["choices"][0]["delta"]["content"], "Par");
+        assert!(content["choices"][0]["delta"]["reasoning_content"].is_null());
+        assert_eq!(terminal["choices"][0]["delta"]["content"], "is");
+        assert_eq!(terminal["choices"][0]["finish_reason"], "stop");
+        assert_eq!(frames.len(), 6);
+    }
+
+    #[tokio::test]
+    async fn streaming_chat_emits_role_deltas_and_usage() {
+        let (choice, tx) = chat_submitted(0);
+        tx.send(chunk("Par", false)).await.unwrap();
+        tx.send(chunk("is", true)).await.unwrap();
+
+        let stream = chat_event_stream(
+            vec![choice],
+            response_processor(None, 1),
+            wire_context(true),
+        );
+        futures::pin_mut!(stream);
+        let frames: Vec<_> = stream
+            .map(|chunk| serde_json::to_value(chunk.unwrap()).unwrap())
+            .collect()
+            .await;
+        assert_eq!(frames.len(), 4);
+        let role = &frames[0];
+        let delta = &frames[1];
+        let terminal = &frames[2];
+        let usage = &frames[3];
+        assert_eq!(role["choices"][0]["delta"]["role"], "assistant");
+        assert!(role["choices"][0]["delta"]["reasoning_content"].is_null());
+        assert_eq!(delta["choices"][0]["delta"]["content"], "Par");
+        assert!(delta["choices"][0]["delta"]["reasoning_content"].is_null());
+        assert_eq!(terminal["choices"][0]["delta"]["content"], "is");
+        assert!(terminal["choices"][0]["delta"]["reasoning_content"].is_null());
+        assert_eq!(terminal["choices"][0]["finish_reason"], "stop");
+        assert_eq!(usage["usage"]["completion_tokens"], 2);
+    }
+
+    #[tokio::test]
+    async fn streaming_chat_waits_for_backend_output_before_role() {
+        let (choice, tx) = chat_submitted(0);
+        let stream = chat_event_stream(
+            vec![choice],
+            response_processor(None, 1),
+            wire_context(false),
+        );
+        futures::pin_mut!(stream);
+
+        assert!(stream.next().now_or_never().is_none());
+
+        tx.send(chunk("Paris", false)).await.unwrap();
+        let role = serde_json::to_value(stream.next().await.unwrap().unwrap()).unwrap();
+        let delta = serde_json::to_value(stream.next().await.unwrap().unwrap()).unwrap();
+        assert_eq!(role["choices"][0]["delta"]["role"], "assistant");
+        assert_eq!(delta["choices"][0]["delta"]["content"], "Paris");
+    }
+
+    #[tokio::test]
+    async fn streaming_chat_stops_all_choices_after_error() {
+        let (choice0, tx0) = chat_submitted(0);
+        let (choice1, tx1) = chat_submitted(1);
+        let stream = chat_event_stream(
+            vec![choice0, choice1],
+            response_processor(None, 2),
+            wire_context(true),
+        );
+        futures::pin_mut!(stream);
+
+        tx0.send(Err(ResponseError {
+            kind: crate::ResponseErrorKind::Upstream(crate::UpstreamErrorCode::Http(429)),
+            message: "out of memory".into(),
+        }))
+        .await
+        .unwrap();
+        let error = stream.next().await.unwrap().unwrap_err();
+        assert_eq!(
+            error.kind,
+            crate::ResponseErrorKind::Upstream(crate::UpstreamErrorCode::Http(429))
+        );
+        assert_eq!(error.message, "out of memory");
+
+        // The other choice may already be ready, but it must not be polled after
+        // the aggregate request has emitted an error.
+        tx1.send(chunk("late", true)).await.unwrap();
+        let remaining = stream.collect::<Vec<_>>().await;
+        assert_eq!(remaining.len(), 1);
+        assert!(
+            remaining
+                .into_iter()
+                .all(|chunk| chunk.unwrap().choices.is_empty())
+        );
+    }
+}

rust/sglang-renderer/src/openai/completions.rs

@@ -0,0 +1,693 @@
+//! OpenAI completion preparation, response aggregation, and typed chunks.
+
+use crate::engine::response::{collect_output, merge_indexed};
+use std::collections::BTreeMap;
+
+use super::{
+    completion_usage,
+    protocol::{
+        CompletionRequest, lower_text_completion_request, lower_token_ids_completion_request,
+        text_completion_prompts, token_ids_completion_prompts,
+    },
+    unix_seconds_u32,
+};
+use crate::{
+    GenerateRequest, GenerationFinishReason, GenerationOutput, GenerationOutputExtras,
+    GenerationStream, MatchedStop, RendererService, ResponseError, engine::TokenDecoder,
+};
+use dynamo_protocols::types::{CompletionUsage, Prompt};
+use futures::StreamExt;
+use serde::Serialize;
+
+pub(crate) struct SubmittedChoice {
+    pub(crate) index: usize,
+    pub(crate) prompt_index: usize,
+    pub(crate) echo: String,
+    pub(crate) events: GenerationStream,
+}
+
+pub(crate) fn attach_streams(
+    metadata: Vec<(usize, usize, String)>,
+    streams: Vec<GenerationStream>,
+) -> Vec<SubmittedChoice> {
+    metadata
+        .into_iter()
+        .zip(streams)
+        .map(|((index, prompt_index, echo), events)| SubmittedChoice {
+            index,
+            prompt_index,
+            echo,
+            events,
+        })
+        .collect()
+}
+#[derive(Debug, Serialize)]
+#[serde(untagged)]
+enum MatchedStopWire {
+    Token(i64),
+    Text(String),
+    Tokens(Vec<i64>),
+}
+
+#[derive(Debug, PartialEq, Serialize)]
+struct CompletionLogprobsWire {
+    tokens: Vec<String>,
+    token_logprobs: Vec<Option<f64>>,
+    top_logprobs: Vec<Option<BTreeMap<String, f64>>>,
+    text_offset: Vec<i32>,
+}
+
+#[derive(Debug, Serialize)]
+struct CompletionChoiceWire {
+    text: String,
+    index: u32,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    logprobs: Option<CompletionLogprobsWire>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    finish_reason: Option<String>,
+    matched_stop: Option<MatchedStopWire>,
+}
+
+#[derive(Debug, Serialize)]
+pub(crate) struct CompletionResponseWire {
+    id: String,
+    choices: Vec<CompletionChoiceWire>,
+    created: u32,
+    model: String,
+    object: &'static str,
+    usage: Option<CompletionUsage>,
+}
+
+struct CompletionResponseContext {
+    metadata: Vec<(usize, usize, String)>,
+    response_id: String,
+    model: String,
+    created: u32,
+    echo: bool,
+    want_logprobs: bool,
+    include_usage: bool,
+    continuous_usage: bool,
+}
+
+pub(crate) async fn prepare_request(
+    renderer: &RendererService,
+    request: &CompletionRequest,
+) -> Result<(String, Vec<GenerateRequest>), ResponseError> {
+    if matches!(&request.prompt, Prompt::String(_) | Prompt::StringArray(_)) {
+        let (response_id, requests) = lower_text_completion_request(renderer.config(), request)?;
+        let requests = renderer.prepare_text_request_groups(requests).await?;
+        Ok((response_id, requests))
+    } else {
+        let (response_id, requests) =
+            lower_token_ids_completion_request(renderer.config(), request)?;
+        let requests = renderer.prepare_token_ids_requests(requests)?;
+        Ok((response_id, requests))
+    }
+}
+
+// Called after request preparation has validated the prompt and choice count.
+fn prepare_response(
+    renderer: &RendererService,
+    tokenizer: &TokenDecoder,
+    request: &CompletionRequest,
+    response_id: String,
+    choice_count: usize,
+) -> Result<CompletionResponseContext, ResponseError> {
+    let echo = request.echo.unwrap_or(false);
+    let n = request.n.unwrap_or(1) as usize;
+    // Echo uses the original input, even when preprocessing truncates engine input IDs.
+    let prompt_echoes = if !echo {
+        vec![String::new(); choice_count / n]
+    } else if matches!(&request.prompt, Prompt::String(_) | Prompt::StringArray(_)) {
+        text_completion_prompts(&request.prompt).map_err(crate::RendererError::from)?
+    } else {
+        token_ids_completion_prompts(&request.prompt)
+            .map_err(crate::RendererError::from)?
+            .into_iter()
+            .map(|ids| tokenizer.detokenize_prompt(ids))
+            .collect::<Result<Vec<_>, _>>()?
+    };
+    let metadata = prompt_echoes
+        .into_iter()
+        .enumerate()
+        .flat_map(|(prompt_index, echo)| {
+            (0..n).map(move |choice| (prompt_index * n + choice, prompt_index, echo.clone()))
+        })
+        .collect();
+    Ok(CompletionResponseContext {
+        metadata,
+        response_id,
+        model: request.model.clone(),
+        created: unix_seconds_u32(),
+        echo,
+        want_logprobs: request.logprobs.is_some(),
+        include_usage: request
+            .stream_options
+            .as_ref()
+            .is_some_and(|options| options.include_usage)
+            || renderer.config().stream_response_default_include_usage,
+        continuous_usage: request
+            .stream_options
+            .as_ref()
+            .is_some_and(|options| options.continuous_usage_stats),
+    })
+}
+
+pub(crate) async fn unary_completion(
+    submitted: Vec<SubmittedChoice>,
+    response_id: String,
+    model: String,
+    created: u32,
+    echo: bool,
+    want_logprobs: bool,
+) -> Result<CompletionResponseWire, ResponseError> {
+    // Every request is already submitted, so draining in choice order does not
+    // serialize generation. The non-streaming native path sends one terminal
+    // result, and the accumulator also tolerates intermediate frames.
+    let mut choices = Vec::with_capacity(submitted.len());
+    let mut prompt_tokens = BTreeMap::<usize, u32>::new();
+    let mut completion_tokens = 0u64;
+
+    for choice in submitted {
+        let output = collect_output(choice.events).await?;
+
+        prompt_tokens
+            .entry(choice.prompt_index)
+            .or_insert(output.prompt_tokens);
+        completion_tokens = completion_tokens.saturating_add(output.completion_tokens);
+        let response_choice = completion_choice(
+            choice.index,
+            if echo {
+                choice.echo + &output.text
+            } else {
+                output.text.clone()
+            },
+            &output,
+            want_logprobs,
+            echo,
+        );
+        choices.push(response_choice);
+    }
+
+    let prompt_tokens = prompt_tokens
+        .values()
+        .copied()
+        .fold(0u32, u32::saturating_add);
+    let usage = completion_usage(
+        prompt_tokens,
+        u32::try_from(completion_tokens).unwrap_or(u32::MAX),
+    );
+
+    Ok(CompletionResponseWire {
+        id: response_id,
+        choices,
+        created,
+        model,
+        object: "text_completion",
+        usage: Some(usage),
+    })
+}
+
+fn completion_choice(
+    index: usize,
+    text: String,
+    output: &GenerationOutput,
+    want_logprobs: bool,
+    include_input_logprobs: bool,
+) -> CompletionChoiceWire {
+    let reason = output.finish_reason.as_ref();
+    let finish_reason = match reason {
+        Some(GenerationFinishReason::Stop(_)) => Some("stop".into()),
+        Some(GenerationFinishReason::Length) => Some("length".into()),
+        Some(GenerationFinishReason::ContentFilter) => Some("content_filter".into()),
+        Some(GenerationFinishReason::Abort) => Some("abort".into()),
+        Some(GenerationFinishReason::Other(other)) => Some(other.clone()),
+        None => None,
+    };
+    let matched_stop = reason
+        .and_then(|reason| match reason {
+            GenerationFinishReason::Stop(matched) => matched.as_ref(),
+            _ => None,
+        })
+        .map(|matched| match matched {
+            MatchedStop::Token(id) => MatchedStopWire::Token(*id),
+            MatchedStop::Text(value) => MatchedStopWire::Text(value.clone()),
+            // Python's OpenAI schema supports an integer or string here, not a
+            // multi-token list. Preserve the native value rather than dropping it.
+            MatchedStop::Tokens(ids) => MatchedStopWire::Tokens(ids.clone()),
+        });
+    CompletionChoiceWire {
+        text,
+        index: u32::try_from(index).unwrap_or(u32::MAX),
+        logprobs: want_logprobs
+            .then(|| completion_logprobs(output.extras.as_deref(), include_input_logprobs)),
+        finish_reason,
+        matched_stop,
+    }
+}
+
+#[allow(clippy::too_many_arguments)]
+pub(crate) fn completion_event_stream(
+    submitted: Vec<SubmittedChoice>,
+    response_id: String,
+    model: String,
+    created: u32,
+    echo: bool,
+    want_logprobs: bool,
+    include_usage: bool,
+    continuous_usage: bool,
+) -> impl futures::Stream<Item = Result<CompletionResponseWire, ResponseError>> {
+    async_stream::stream! {
+        let count = submitted.len();
+        let mut prompt_indexes = Vec::with_capacity(count);
+        let mut echoes = Vec::with_capacity(count);
+        let mut first_chunks = vec![true; count];
+        let mut prompt_tokens_by_prompt = BTreeMap::<usize, u32>::new();
+        let mut completion_tokens_by_choice = vec![0u64; count];
+        let mut streams = Vec::with_capacity(count);
+
+        for choice in submitted {
+            prompt_indexes.push(choice.prompt_index);
+            echoes.push(choice.echo);
+            streams.push(choice.events);
+        }
+        let mut events = merge_indexed(streams);
+
+        while let Some((index, item)) = events.next().await {
+            let output = match item {
+                Ok(output) => output,
+                Err(error) => {
+                    yield Err(error);
+                    break;
+                }
+            };
+
+            prompt_tokens_by_prompt
+                .entry(prompt_indexes[index])
+                .or_insert(output.prompt_tokens);
+            completion_tokens_by_choice[index] = completion_tokens_by_choice[index]
+                .saturating_add(output.completion_tokens);
+            let first = std::mem::replace(&mut first_chunks[index], false);
+            let text = if echo && first {
+                echoes[index].clone() + &output.text
+            } else {
+                output.text.clone()
+            };
+            let chunk_usage = continuous_usage.then(|| {
+                completion_usage(
+                    output.prompt_tokens,
+                    u32::try_from(completion_tokens_by_choice[index]).unwrap_or(u32::MAX),
+                )
+            });
+            let choice = completion_choice(
+                index,
+                text,
+                &output,
+                want_logprobs,
+                echo && first,
+            );
+            let chunk = CompletionResponseWire {
+                id: response_id.clone(),
+                choices: vec![choice],
+                created,
+                model: model.clone(),
+                object: "text_completion",
+                usage: chunk_usage,
+            };
+            yield Ok(chunk);
+        }
+
+        if include_usage {
+            let prompt_tokens = prompt_tokens_by_prompt
+                .values()
+                .copied()
+                .fold(0u32, u32::saturating_add);
+            let completion_tokens = completion_tokens_by_choice
+                .into_iter()
+                .fold(0u64, u64::saturating_add);
+            let final_chunk = CompletionResponseWire {
+                id: response_id,
+                choices: vec![],
+                created,
+                model,
+                object: "text_completion",
+                usage: Some(completion_usage(
+                    prompt_tokens,
+                    u32::try_from(completion_tokens).unwrap_or(u32::MAX),
+                )),
+            };
+            yield Ok(final_chunk);
+        }
+    }
+}
+
+fn completion_logprobs(
+    extras: Option<&GenerationOutputExtras>,
+    include_input: bool,
+) -> CompletionLogprobsWire {
+    let mut result = CompletionLogprobsWire {
+        tokens: Vec::new(),
+        token_logprobs: Vec::new(),
+        top_logprobs: Vec::new(),
+        text_offset: Vec::new(),
+    };
+    let Some(extras) = extras else {
+        return result;
+    };
+    if include_input {
+        append_logprobs(&mut result, &extras.input_logprobs);
+    }
+    append_logprobs(&mut result, &extras.output_logprobs);
+    result
+}
+
+fn append_logprobs(result: &mut CompletionLogprobsWire, positions: &[crate::PositionLogprobs]) {
+    for position in positions {
+        let selected = &position.token;
+        result.tokens.push(
+            selected
+                .text
+                .clone()
+                .unwrap_or_else(|| format!("token_id:{}", selected.token_id)),
+        );
+        // Python exposes the engine's f32 values as double-precision JSON numbers.
+        result.token_logprobs.push(selected.logprob.map(f64::from));
+        result.text_offset.push(-1);
+        if position.top.is_empty() {
+            result.top_logprobs.push(None);
+            continue;
+        }
+        let mut top = BTreeMap::new();
+        for candidate in &position.top {
+            let Some(logprob) = candidate.logprob else {
+                continue;
+            };
+            top.insert(
+                candidate
+                    .text
+                    .clone()
+                    .unwrap_or_else(|| format!("token_id:{}", candidate.token_id)),
+                f64::from(logprob),
+            );
+        }
+        result.top_logprobs.push(Some(top));
+    }
+}
+
+impl super::OpenAIService {
+    pub(crate) async fn complete(
+        &self,
+        request: CompletionRequest,
+    ) -> Result<
+        super::OperationResponse<CompletionResponseWire, CompletionResponseWire>,
+        ResponseError,
+    > {
+        use super::OperationResponse;
+        let stream = request.stream.unwrap_or(false);
+        let (response_id, requests) = prepare_request(&self.renderer, &request).await?;
+        let context = prepare_response(
+            &self.renderer,
+            &self.generation.decoder,
+            &request,
+            response_id,
+            requests.len(),
+        )?;
+        let streams = match self.generation.generate_many(requests).await {
+            Ok(streams) => streams,
+            Err(error) if stream => {
+                return Ok(OperationResponse::Stream(
+                    futures::stream::once(async { Err(error) }).boxed(),
+                ));
+            }
+            Err(error) => return Err(error),
+        };
+        let submitted = attach_streams(context.metadata, streams);
+        if stream {
+            Ok(OperationResponse::Stream(
+                completion_event_stream(
+                    submitted,
+                    context.response_id,
+                    context.model,
+                    context.created,
+                    context.echo,
+                    context.want_logprobs,
+                    context.include_usage,
+                    context.continuous_usage,
+                )
+                .boxed(),
+            ))
+        } else {
+            unary_completion(
+                submitted,
+                context.response_id,
+                context.model,
+                context.created,
+                context.echo,
+                context.want_logprobs,
+            )
+            .await
+            .map(OperationResponse::Unary)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{
+        completion_event_stream, completion_logprobs, prepare_request, prepare_response,
+        unary_completion,
+    };
+    use crate::GenerationOutputExtras;
+    use crate::engine::{TokenDecoder, test_utils::tiny_tokenizer};
+    use crate::openai::test_utils::{chunk, renderer_config, submitted};
+    use crate::{DynamoTokenizer, PositionLogprobs, RendererService, ResponseError, TokenLogprob};
+    use futures::StreamExt;
+    use std::sync::Arc;
+
+    #[tokio::test]
+    async fn completion_response_preserves_batched_echo_before_truncation() {
+        let tokenizer = tiny_tokenizer();
+        let prompts = ["hello", "world"];
+        let token_ids =
+            prompts.map(|prompt| tokenizer.encode(prompt).unwrap().token_ids().to_vec());
+        for truncate in [false, true] {
+            let mut config = renderer_config();
+            if truncate {
+                config.limits.context_len = 2;
+                config.limits.allow_auto_truncate = true;
+                assert!(token_ids.iter().all(|ids| ids.len() > 2));
+            }
+            let renderer = RendererService::with_tokenizer(
+                config,
+                Arc::new(DynamoTokenizer::new(tokenizer.clone(), tokenizer.clone())),
+                1,
+                1,
+            );
+            for tokenized in [false, true] {
+                for echo in [false, true] {
+                    let prompt = if tokenized {
+                        serde_json::json!(token_ids)
+                    } else {
+                        serde_json::json!(prompts)
+                    };
+                    let request = serde_json::from_value(serde_json::json!({
+                        "model": "model", "prompt": prompt, "n": 2, "echo": echo,
+                        "rid": ["prompt-a", "prompt-b"], "max_tokens": 4, "logprobs": 0
+                    }))
+                    .unwrap();
+                    let (response_id, requests) =
+                        prepare_request(&renderer, &request).await.unwrap();
+                    let context = prepare_response(
+                        &renderer,
+                        &TokenDecoder::new(tokenizer.clone()),
+                        &request,
+                        response_id,
+                        requests.len(),
+                    )
+                    .unwrap();
+
+                    assert_eq!(requests.len(), 4);
+                    assert_eq!(context.metadata.len(), 4);
+                    assert_eq!(context.echo, echo);
+                    for (index, (request, metadata)) in
+                        requests.iter().zip(&context.metadata).enumerate()
+                    {
+                        let prompt_index = index / 2;
+                        let expected_echo = if !echo {
+                            String::new()
+                        } else if tokenized {
+                            String::from(tokenizer.decode(&token_ids[prompt_index], true).unwrap())
+                        } else {
+                            prompts[prompt_index].to_owned()
+                        };
+                        assert_eq!(metadata, &(index, prompt_index, expected_echo));
+                        let mut expected_ids = token_ids[prompt_index]
+                            .iter()
+                            .map(|&id| id as i32)
+                            .collect::<Vec<_>>();
+                        if truncate {
+                            expected_ids.truncate(2);
+                        }
+                        assert_eq!(request.input_ids, expected_ids);
+                        assert_eq!(request.logprob_start_len, if echo { 0 } else { -1 });
+                        assert_eq!(
+                            request.rid,
+                            format!(
+                                "prompt-{}-{}",
+                                if prompt_index == 0 { "a" } else { "b" },
+                                index % 2
+                            )
+                        );
+                    }
+                }
+            }
+        }
+    }
+
+    #[test]
+    fn serialized_logprobs_preserve_python_float_values() {
+        let selected = -1.586831_f32;
+        let alternative = -2.7182817_f32;
+        let extras = GenerationOutputExtras {
+            output_logprobs: vec![PositionLogprobs {
+                token: TokenLogprob {
+                    logprob: Some(selected),
+                    token_id: 7,
+                    text: Some("x".into()),
+                },
+                top: vec![TokenLogprob {
+                    logprob: Some(alternative),
+                    token_id: 8,
+                    text: Some("y".into()),
+                }],
+            }],
+            ..Default::default()
+        };
+        // Exercise the wire serializer: to_value widens f32 before encoding it.
+        let json = serde_json::to_string(&completion_logprobs(Some(&extras), false)).unwrap();
+        let wire: serde_json::Value = serde_json::from_str(&json).unwrap();
+        assert_eq!(
+            wire["token_logprobs"][0].as_f64(),
+            Some(f64::from(selected))
+        );
+        assert_eq!(
+            wire["top_logprobs"][0]["y"].as_f64(),
+            Some(f64::from(alternative))
+        );
+    }
+
+    #[test]
+    fn zero_top_logprobs_keeps_selected_token_and_empty_top_map() {
+        let extras = GenerationOutputExtras {
+            output_logprobs: vec![PositionLogprobs {
+                token: TokenLogprob {
+                    logprob: Some(-0.25),
+                    token_id: 7,
+                    text: Some("x".into()),
+                },
+                top: Vec::new(),
+            }],
+            ..Default::default()
+        };
+        let logprobs = completion_logprobs(Some(&extras), false);
+        assert_eq!(logprobs.tokens, ["x"]);
+        assert_eq!(logprobs.token_logprobs, [Some(-0.25)]);
+        assert_eq!(logprobs.top_logprobs, [None]);
+        assert_eq!(logprobs.text_offset, [-1]);
+    }
+
+    #[tokio::test]
+    async fn unary_fold_orders_choices_and_counts_each_prompt_once() {
+        let (choice0, tx0) = submitted(0, 0);
+        let (choice1, tx1) = submitted(1, 0);
+        tx0.send(chunk("a", false)).await.unwrap();
+        tx0.send(chunk("b", true)).await.unwrap();
+        tx1.send(chunk("x", false)).await.unwrap();
+        tx1.send(chunk("y", true)).await.unwrap();
+
+        let response = unary_completion(
+            vec![choice0, choice1],
+            "cmpl-test".into(),
+            "model".into(),
+            1,
+            false,
+            false,
+        )
+        .await;
+        let value = serde_json::to_value(response.unwrap()).unwrap();
+        assert_eq!(value["choices"][0]["text"], "ab");
+        assert_eq!(value["choices"][1]["text"], "xy");
+        assert_eq!(value["choices"][0]["matched_stop"], "</s>");
+        assert!(value.get("system_fingerprint").is_none());
+        assert_eq!(value["usage"]["prompt_tokens"], 5);
+        assert_eq!(value["usage"]["completion_tokens"], 4);
+    }
+
+    #[tokio::test]
+    async fn stream_uses_deltas_then_usage() {
+        let (choice, tx) = submitted(0, 0);
+        tx.send(chunk("a", false)).await.unwrap();
+        tx.send(chunk("b", true)).await.unwrap();
+
+        let stream = completion_event_stream(
+            vec![choice],
+            "cmpl-test".into(),
+            "model".into(),
+            1,
+            false,
+            false,
+            true,
+            false,
+        );
+        futures::pin_mut!(stream);
+        let frames: Vec<_> = stream
+            .map(|chunk| serde_json::to_value(chunk.unwrap()).unwrap())
+            .collect()
+            .await;
+        assert_eq!(frames.len(), 3);
+        let first = &frames[0];
+        let terminal = &frames[1];
+        let usage = &frames[2];
+        assert_eq!(first["choices"][0]["text"], "a");
+        assert_eq!(terminal["choices"][0]["text"], "b");
+        assert_eq!(terminal["choices"][0]["finish_reason"], "stop");
+        assert!(usage["choices"].as_array().unwrap().is_empty());
+        assert_eq!(usage["usage"]["prompt_tokens"], 5);
+        assert_eq!(usage["usage"]["completion_tokens"], 2);
+    }
+
+    #[tokio::test]
+    async fn stream_stops_all_choices_after_error() {
+        let (choice0, tx0) = submitted(0, 0);
+        let (choice1, tx1) = submitted(1, 0);
+        let stream = completion_event_stream(
+            vec![choice0, choice1],
+            "cmpl-test".into(),
+            "model".into(),
+            1,
+            false,
+            false,
+            true,
+            false,
+        );
+        futures::pin_mut!(stream);
+
+        tx0.send(Err(ResponseError {
+            kind: crate::ResponseErrorKind::Unavailable,
+            message: "out of memory".into(),
+        }))
+        .await
+        .unwrap();
+        let error = stream.next().await.unwrap().unwrap_err();
+        assert_eq!(error.kind, crate::ResponseErrorKind::Unavailable);
+
+        tx1.send(chunk("late", true)).await.unwrap();
+        let remaining = stream.collect::<Vec<_>>().await;
+        assert_eq!(remaining.len(), 1);
+        assert!(
+            remaining
+                .into_iter()
+                .all(|chunk| chunk.unwrap().choices.is_empty())
+        );
+    }
+}

rust/sglang-renderer/src/openai/mod.rs

@@ -0,0 +1,67 @@
+//! OpenAI request preparation and typed response construction.
+
+use crate::ResponseError;
+use dynamo_protocols::types::CompletionUsage;
+
+pub(crate) mod chat;
+pub(crate) mod completions;
+pub(crate) mod protocol;
+pub(crate) mod render;
+pub(crate) mod tokenize;
+
+#[cfg(test)]
+pub(crate) mod test_utils;
+#[cfg(test)]
+mod tests;
+
+pub(super) fn unix_seconds_u32() -> u32 {
+    std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .map(|duration| u32::try_from(duration.as_secs()).unwrap_or(u32::MAX))
+        .unwrap_or(0)
+}
+
+pub(super) fn completion_usage(prompt_tokens: u32, completion_tokens: u32) -> CompletionUsage {
+    CompletionUsage {
+        prompt_tokens,
+        completion_tokens,
+        total_tokens: prompt_tokens.saturating_add(completion_tokens),
+        ..Default::default()
+    }
+}
+
+/// Typed route result; transport adapters supply framing and status policy.
+pub(crate) enum OperationResponse<U, C> {
+    Unary(U),
+    Stream(futures::stream::BoxStream<'static, Result<C, ResponseError>>),
+}
+
+pub(crate) struct OpenAIService {
+    pub(crate) renderer: std::sync::Arc<crate::RendererService>,
+    generation: crate::engine::GenerationService,
+}
+
+impl OpenAIService {
+    pub(crate) fn new(
+        renderer: std::sync::Arc<crate::RendererService>,
+        generation: crate::engine::GenerationService,
+    ) -> Self {
+        Self {
+            renderer,
+            generation,
+        }
+    }
+}
+
+pub(crate) fn error_payload(
+    code: u16,
+    message: impl Into<String>,
+    error_type: &str,
+) -> serde_json::Value {
+    serde_json::json!({
+        "error": {
+            "object": "error", "message": message.into(), "type": error_type,
+            "param": null, "code": code,
+        }
+    })
+}

rust/sglang-renderer/src/openai/protocol.rs

@@ -0,0 +1,784 @@
+//! OpenAI wire types lowered into renderer-owned requests.
+
+use std::collections::{BTreeMap, HashMap};
+
+use dynamo_protocols::types::{
+    ChatCompletionAudio, ChatCompletionFunctionCall, ChatCompletionFunctions,
+    ChatCompletionRequestMessage, ChatCompletionStreamOptions, ChatCompletionTool,
+    ChatCompletionToolChoiceOption, PredictionContent, Prompt, ResponseFormat, ServiceTier, Stop,
+    WebSearchOptions,
+};
+use serde::Deserialize;
+use serde_json::Value;
+
+use crate::preprocessing::{GenerateRequestIdentity, TextRequestGroup};
+use crate::{
+    ChatRequest, GenerateRequestMetadata, GenerationOptions, OneOrMany, ReasoningEffort,
+    RendererConfig, RendererError, SamplingDefaults, SamplingParams, SamplingParamsOverrides,
+    TokenIds, TokenIdsRequest,
+};
+
+const MAX_OPENAI_CHOICES: usize = 4096;
+
+#[derive(Deserialize, PartialEq)]
+#[serde(rename_all = "lowercase")]
+enum ResponseModality {
+    Text,
+    Audio,
+}
+
+fn reject_unsupported_fields(fields: &HashMap<String, Value>) -> Result<(), String> {
+    if fields.is_empty() {
+        return Ok(());
+    }
+    let mut names = fields.keys().cloned().collect::<Vec<_>>();
+    names.sort_unstable();
+    Err(format!(
+        "unsupported request field{}: {}",
+        if names.len() == 1 { "" } else { "s" },
+        names.join(", ")
+    ))
+}
+
+/// SGLang's OpenAI-compatible chat-completions request.
+#[derive(Deserialize)]
+pub(crate) struct ChatCompletionRequest {
+    pub messages: Vec<ChatCompletionRequestMessage>,
+    pub model: String,
+    #[serde(default)]
+    pub mm_processor_kwargs: Option<Value>,
+    #[serde(default)]
+    pub store: Option<bool>,
+    #[serde(default)]
+    pub reasoning_effort: Option<ReasoningEffort>,
+    #[serde(default)]
+    pub reasoning: Option<Value>,
+    #[serde(default)]
+    pub metadata: Option<Value>,
+    #[serde(default)]
+    pub frequency_penalty: Option<f32>,
+    #[serde(default)]
+    pub logit_bias: Option<HashMap<String, Value>>,
+    #[serde(default)]
+    pub logprobs: Option<bool>,
+    #[serde(default)]
+    pub top_logprobs: Option<u8>,
+    #[serde(default)]
+    pub max_tokens: Option<u32>,
+    #[serde(default)]
+    pub max_completion_tokens: Option<u32>,
+    #[serde(default)]
+    pub n: Option<u8>,
+    #[serde(default)]
+    modalities: Option<Vec<ResponseModality>>,
+    #[serde(default)]
+    pub prediction: Option<PredictionContent>,
+    #[serde(default)]
+    pub audio: Option<ChatCompletionAudio>,
+    #[serde(default)]
+    pub presence_penalty: Option<f32>,
+    #[serde(default)]
+    pub response_format: Option<ResponseFormat>,
+    #[serde(default)]
+    pub seed: Option<i64>,
+    #[serde(default)]
+    pub service_tier: Option<ServiceTier>,
+    #[serde(default)]
+    pub stop: Option<Stop>,
+    #[serde(default)]
+    pub stream: Option<bool>,
+    #[serde(default)]
+    pub stream_options: Option<ChatCompletionStreamOptions>,
+    #[serde(default)]
+    pub temperature: Option<f32>,
+    #[serde(default)]
+    pub top_p: Option<f32>,
+    #[serde(default)]
+    pub tools: Option<Vec<ChatCompletionTool>>,
+    #[serde(default)]
+    pub tool_choice: Option<ChatCompletionToolChoiceOption>,
+    #[serde(default)]
+    pub parallel_tool_calls: Option<bool>,
+    #[serde(default)]
+    pub user: Option<String>,
+    #[serde(default)]
+    pub function_call: Option<ChatCompletionFunctionCall>,
+    #[serde(default)]
+    pub functions: Option<Vec<ChatCompletionFunctions>>,
+    #[serde(default)]
+    pub web_search_options: Option<WebSearchOptions>,
+    #[serde(default)]
+    pub chat_template_kwargs: Option<HashMap<String, Value>>,
+    #[serde(default)]
+    pub continue_final_message: bool,
+    #[serde(flatten)]
+    pub sampling_overrides: SamplingParamsOverrides,
+    #[serde(flatten)]
+    pub extensions: RequestExtensions,
+    #[serde(flatten)]
+    pub unsupported_fields: HashMap<String, Value>,
+}
+
+/// SGLang's OpenAI-compatible legacy-completions request.
+#[derive(Deserialize)]
+pub(crate) struct CompletionRequest {
+    pub model: String,
+    pub prompt: Prompt,
+    #[serde(default)]
+    pub prompt_embeds: Option<String>,
+    #[serde(default)]
+    pub suffix: Option<String>,
+    #[serde(default)]
+    pub max_tokens: Option<u32>,
+    #[serde(default)]
+    pub temperature: Option<f32>,
+    #[serde(default)]
+    pub top_p: Option<f32>,
+    #[serde(default)]
+    pub n: Option<u8>,
+    #[serde(default)]
+    pub stream: Option<bool>,
+    #[serde(default)]
+    pub stream_options: Option<ChatCompletionStreamOptions>,
+    #[serde(default)]
+    pub logprobs: Option<u8>,
+    #[serde(default)]
+    pub echo: Option<bool>,
+    #[serde(default)]
+    pub stop: Option<Stop>,
+    #[serde(default)]
+    pub presence_penalty: Option<f32>,
+    #[serde(default)]
+    pub frequency_penalty: Option<f32>,
+    #[serde(default)]
+    pub best_of: Option<u8>,
+    #[serde(default)]
+    pub logit_bias: Option<HashMap<String, Value>>,
+    #[serde(default)]
+    pub user: Option<String>,
+    #[serde(default)]
+    pub seed: Option<i64>,
+    #[serde(flatten)]
+    pub sampling_overrides: SamplingParamsOverrides,
+    #[serde(flatten)]
+    pub extensions: RequestExtensions,
+    #[serde(flatten)]
+    pub unsupported_fields: HashMap<String, Value>,
+}
+
+/// SGLang extensions carried by the OpenAI-compatible request contract.
+#[derive(Clone, Debug, Default, Deserialize)]
+pub(crate) struct RequestExtensions {
+    #[serde(default)]
+    pub return_meta_info: Option<bool>,
+    #[serde(default)]
+    pub rid: Option<OneOrMany<String>>,
+    #[serde(default)]
+    pub cache_salt: Option<OneOrMany<String>>,
+    #[serde(default)]
+    pub extra_key: Option<OneOrMany<String>>,
+    #[serde(default)]
+    pub priority: Option<i64>,
+    #[serde(default)]
+    pub bootstrap_host: Option<OneOrMany<String>>,
+    #[serde(default)]
+    pub bootstrap_port: Option<OneOrMany<Option<i64>>>,
+    #[serde(default)]
+    pub bootstrap_room: Option<OneOrMany<i64>>,
+    #[serde(default)]
+    pub routed_dp_rank: Option<i64>,
+    #[serde(default)]
+    pub disagg_prefill_dp_rank: Option<i64>,
+    #[serde(default)]
+    pub data_parallel_rank: Option<i64>,
+    #[serde(default)]
+    pub session_id: Option<serde_json::Value>,
+    #[serde(default)]
+    pub session_params: Option<serde_json::Value>,
+    #[serde(default)]
+    pub lora_path: Option<serde_json::Value>,
+    #[serde(default)]
+    pub custom_logit_processor: Option<serde_json::Value>,
+    #[serde(default)]
+    pub image_data: Option<serde_json::Value>,
+    #[serde(default)]
+    pub video_data: Option<serde_json::Value>,
+    #[serde(default)]
+    pub audio_data: Option<serde_json::Value>,
+    #[serde(default)]
+    pub mm_hashes: Option<serde_json::Value>,
+}
+
+#[derive(Debug)]
+struct ExpandedRequestContext {
+    request_id: String,
+    metadata: GenerateRequestMetadata,
+}
+
+impl RequestExtensions {
+    fn validate(&self) -> Result<(), String> {
+        for (name, value) in [
+            ("session_id", &self.session_id),
+            ("session_params", &self.session_params),
+            ("lora_path", &self.lora_path),
+            ("custom_logit_processor", &self.custom_logit_processor),
+            ("image_data", &self.image_data),
+            ("video_data", &self.video_data),
+            ("audio_data", &self.audio_data),
+            ("mm_hashes", &self.mm_hashes),
+        ] {
+            if value.is_some() {
+                return Err(format!(
+                    "{name} is not supported by the text-only Rust frontend"
+                ));
+            }
+        }
+        Ok(())
+    }
+
+    fn response_id(&self, prefix: &str) -> String {
+        match self.rid.as_ref() {
+            Some(OneOrMany::One(rid)) => rid.clone(),
+            Some(OneOrMany::Many(rids)) => rids
+                .first()
+                .cloned()
+                .unwrap_or_else(|| generated_response_id(prefix)),
+            None => generated_response_id(prefix),
+        }
+    }
+
+    fn expand(
+        self,
+        model: String,
+        prompt_count: usize,
+        choice_count: usize,
+        response_id: &str,
+    ) -> Result<Vec<ExpandedRequestContext>, String> {
+        let list_rids = matches!(&self.rid, Some(OneOrMany::Many(_)));
+        let rids = expand_per_prompt("rid", self.rid, prompt_count)?;
+        if list_rids {
+            let mut seen = std::collections::HashSet::new();
+            for rid in rids.iter().flatten() {
+                if !seen.insert(rid) {
+                    return Err(format!("duplicate request ID in rid: {rid}"));
+                }
+            }
+        }
+        let cache_salts = expand_per_prompt("cache_salt", self.cache_salt, prompt_count)?;
+        let extra_keys = expand_per_prompt("extra_key", self.extra_key, prompt_count)?;
+        let bootstrap_hosts =
+            expand_per_prompt("bootstrap_host", self.bootstrap_host, prompt_count)?;
+        let bootstrap_ports =
+            expand_per_prompt("bootstrap_port", self.bootstrap_port, prompt_count)?;
+        let bootstrap_rooms = match self.bootstrap_room {
+            Some(OneOrMany::One(base)) => (0..prompt_count)
+                .map(|prompt_index| {
+                    let offset = i64::try_from(prompt_index)
+                        .map_err(|_| "bootstrap_room prompt index exceeds i64".to_owned())?;
+                    base.checked_add(offset)
+                        .map(Some)
+                        .ok_or_else(|| "bootstrap_room overflows i64".to_owned())
+                })
+                .collect::<Result<Vec<_>, _>>()?,
+            value => expand_per_prompt("bootstrap_room", value, prompt_count)?,
+        };
+        let routed_dp_rank = self.routed_dp_rank.or(self.data_parallel_rank);
+        let total = prompt_count
+            .checked_mul(choice_count)
+            .ok_or_else(|| "prompt count times n overflows usize".to_owned())?;
+        let mut contexts = Vec::with_capacity(total);
+        for prompt_index in 0..prompt_count {
+            for sample_index in 0..choice_count {
+                let index = prompt_index * choice_count + sample_index;
+                let request_id = match (&rids[prompt_index], list_rids) {
+                    (Some(rid), true) if choice_count == 1 => rid.clone(),
+                    (Some(rid), true) => format!("{rid}-{sample_index}"),
+                    _ => format!("{response_id}-{index}"),
+                };
+                contexts.push(ExpandedRequestContext {
+                    request_id,
+                    metadata: GenerateRequestMetadata {
+                        model: Some(model.clone()),
+                        cache_salt: cache_salts[prompt_index]
+                            .clone()
+                            .filter(|value| !value.is_empty()),
+                        extra_key: extra_keys[prompt_index]
+                            .clone()
+                            .filter(|value| !value.is_empty()),
+                        priority: self.priority,
+                        bootstrap_host: bootstrap_hosts[prompt_index].clone(),
+                        bootstrap_port: bootstrap_ports[prompt_index].flatten(),
+                        bootstrap_room: bootstrap_rooms[prompt_index],
+                        routed_dp_rank,
+                        disagg_prefill_dp_rank: self.disagg_prefill_dp_rank,
+                    },
+                });
+            }
+        }
+        Ok(contexts)
+    }
+}
+
+fn expand_per_prompt<T: Clone>(
+    name: &str,
+    value: Option<OneOrMany<T>>,
+    prompt_count: usize,
+) -> Result<Vec<Option<T>>, String> {
+    match value {
+        None => Ok(vec![None; prompt_count]),
+        Some(OneOrMany::One(value)) => Ok(vec![Some(value); prompt_count]),
+        Some(OneOrMany::Many(values)) if values.len() == prompt_count => {
+            Ok(values.into_iter().map(Some).collect())
+        }
+        Some(OneOrMany::Many(values)) => Err(format!(
+            "the length of {name} must equal the prompt batch size ({prompt_count}), got {}",
+            values.len()
+        )),
+    }
+}
+
+fn generated_response_id(prefix: &str) -> String {
+    format!("{prefix}-{}", uuid::Uuid::new_v4().simple())
+}
+
+/// Lower the OpenAI Chat wire type into the structured internal chat request.
+/// Chat template rendering and tool constraints deliberately happen later in
+/// `ChatPreprocessor`, where every transport shares them.
+pub(crate) fn lower_chat_request(
+    config: &RendererConfig,
+    mut request: ChatCompletionRequest,
+) -> Result<(String, ChatRequest), RendererError> {
+    normalize_reasoning_inputs(
+        &mut request.reasoning_effort,
+        request.reasoning.take(),
+        &mut request.chat_template_kwargs,
+    )?;
+    // Accepted OpenAI metadata fields do not affect SGLang generation.
+    let _ = (&request.store, &request.metadata, &request.user);
+    reject_unsupported_fields(&request.unsupported_fields)?;
+    request.extensions.validate()?;
+    validate_chat_request(config, &request)?;
+    let response_id = request.extensions.response_id("chatcmpl");
+    let metadata = request
+        .extensions
+        .clone()
+        .expand(request.model.clone(), 1, 1, &response_id)?
+        .pop()
+        .expect("one chat prompt produces one metadata context")
+        .metadata;
+    let mut sampling_params = chat_sampling_params(&request, &config.default_sampling_params)?;
+    request.sampling_overrides.apply(&mut sampling_params);
+    Ok((
+        response_id.clone(),
+        ChatRequest {
+            rid: response_id,
+            model: request.model,
+            messages: request.messages,
+            tools: request.tools,
+            tool_choice: request.tool_choice,
+            response_format: request.response_format,
+            reasoning_effort: request.reasoning_effort,
+            continue_final_message: request.continue_final_message,
+            chat_template_args: request.chat_template_kwargs,
+            sampling_params,
+            choice_count: request.n.unwrap_or(1) as usize,
+            stream: request.stream.unwrap_or(false),
+            return_logprob: request.logprobs.unwrap_or(false),
+            top_logprobs_num: request.top_logprobs.unwrap_or(0) as i64,
+            parallel_tool_calls: request.parallel_tool_calls.unwrap_or(true),
+            metadata,
+        },
+    ))
+}
+
+pub(crate) fn normalize_reasoning_inputs(
+    reasoning_effort: &mut Option<ReasoningEffort>,
+    reasoning: Option<Value>,
+    chat_template_kwargs: &mut Option<HashMap<String, Value>>,
+) -> Result<(), RendererError> {
+    let mut thinking = None;
+    if let Some(Value::Object(reasoning)) = reasoning {
+        let nested_effort = reasoning
+            .get("effort")
+            .filter(|value| !value.is_null())
+            .or_else(|| {
+                reasoning
+                    .get("reasoning_effort")
+                    .filter(|value| !value.is_null())
+            });
+        if let Some(nested_effort) = nested_effort {
+            *reasoning_effort = Some(
+                serde_json::from_value(nested_effort.clone())
+                    .map_err(|error| format!("invalid reasoning effort: {error}"))?,
+            );
+        }
+
+        let enabled = reasoning
+            .get("enabled")
+            .filter(|value| !value.is_null())
+            .or_else(|| reasoning.get("enable"));
+        if enabled.is_some_and(json_truthy) {
+            thinking = Some(true);
+        }
+    }
+
+    if let Some(effort) = reasoning_effort.as_ref() {
+        thinking = Some(!effort.disables_thinking());
+    }
+    if let Some(thinking) = thinking {
+        let args = chat_template_kwargs.get_or_insert_with(HashMap::new);
+        args.entry("thinking".into()).or_insert(thinking.into());
+        args.entry("enable_thinking".into())
+            .or_insert(thinking.into());
+    }
+    Ok(())
+}
+
+fn json_truthy(value: &Value) -> bool {
+    match value {
+        Value::Null => false,
+        Value::Bool(value) => *value,
+        Value::Number(value) => value.as_f64().is_some_and(|value| value != 0.0),
+        Value::String(value) => matches!(
+            value.trim().to_ascii_lowercase().as_str(),
+            "1" | "true" | "yes" | "y" | "on"
+        ),
+        Value::Array(value) => !value.is_empty(),
+        Value::Object(value) => !value.is_empty(),
+    }
+}
+
+fn validate_chat_request(
+    config: &RendererConfig,
+    request: &ChatCompletionRequest,
+) -> Result<(), RendererError> {
+    if request.model != config.served_model_name {
+        return Err(format!("The model `{}` does not exist", request.model).into());
+    }
+    if request.n == Some(0) {
+        return Err("n must be at least 1".into());
+    }
+    if request.extensions.return_meta_info == Some(true) {
+        return Err("return_meta_info=true is not supported by the renderer".into());
+    }
+    #[allow(deprecated)]
+    let max_tokens = request.max_completion_tokens.or(request.max_tokens);
+    if max_tokens == Some(0) {
+        return Err("max_completion_tokens must be positive".into());
+    }
+    if request
+        .modalities
+        .as_ref()
+        .is_some_and(|modalities| modalities.contains(&ResponseModality::Audio))
+        || request.audio.is_some()
+        || request.prediction.is_some()
+        || request.web_search_options.is_some()
+        || request.mm_processor_kwargs.is_some()
+    {
+        return Err(
+            "audio, prediction, web search, and multimodal inputs are not supported".into(),
+        );
+    }
+    #[allow(deprecated)]
+    if request.function_call.is_some() || request.functions.is_some() {
+        return Err(
+            "deprecated function_call/functions are not supported; use tools and tool_choice"
+                .into(),
+        );
+    }
+    Ok(())
+}
+
+#[allow(deprecated)]
+pub fn chat_sampling_params(
+    request: &ChatCompletionRequest,
+    model_defaults: &SamplingDefaults,
+) -> Result<SamplingParams, String> {
+    let defaults = sampling_params_with_model_defaults(model_defaults);
+    let mut stop = None;
+    let mut stop_token_ids = None;
+    match request.stop.as_ref() {
+        Some(Stop::String(value)) => stop = Some(OneOrMany::One(value.clone())),
+        Some(Stop::StringArray(values)) => stop = Some(OneOrMany::Many(values.clone())),
+        Some(Stop::TokenIdArray(values)) => {
+            stop_token_ids = Some(values.iter().map(|&id| id as i64).collect())
+        }
+        None => {}
+    }
+    let mut logit_bias = BTreeMap::new();
+    if let Some(values) = request.logit_bias.as_ref() {
+        for (token, bias) in values {
+            let bias = bias
+                .as_f64()
+                .ok_or_else(|| format!("logit_bias[{token:?}] must be a number"))?;
+            logit_bias.insert(token.clone(), bias);
+        }
+    }
+    let json_schema = match request.response_format.as_ref() {
+        Some(ResponseFormat::JsonSchema { json_schema }) => Some(json_schema.schema.to_string()),
+        Some(ResponseFormat::JsonObject) => Some(r#"{"type":"object"}"#.into()),
+        _ => None,
+    };
+
+    Ok(SamplingParams {
+        max_new_tokens: request
+            .max_completion_tokens
+            .or(request.max_tokens)
+            .map(i64::from),
+        stop,
+        stop_token_ids,
+        temperature: request
+            .temperature
+            .map(f64::from)
+            .unwrap_or(defaults.temperature),
+        top_p: request.top_p.map(f64::from).unwrap_or(defaults.top_p),
+        frequency_penalty: request.frequency_penalty.unwrap_or(0.0) as f64,
+        presence_penalty: request.presence_penalty.unwrap_or(0.0) as f64,
+        n: 1,
+        logit_bias: (!logit_bias.is_empty()).then_some(logit_bias),
+        sampling_seed: request.seed,
+        json_schema,
+        ..defaults
+    })
+}
+
+fn sampling_params_with_model_defaults(model_defaults: &SamplingDefaults) -> SamplingParams {
+    let terminals = SamplingParams::default();
+    SamplingParams {
+        temperature: model_defaults.temperature.unwrap_or(terminals.temperature),
+        top_p: model_defaults.top_p.unwrap_or(terminals.top_p),
+        top_k: model_defaults.top_k.unwrap_or(terminals.top_k),
+        min_p: model_defaults.min_p.unwrap_or(terminals.min_p),
+        repetition_penalty: model_defaults
+            .repetition_penalty
+            .unwrap_or(terminals.repetition_penalty),
+        ..terminals
+    }
+}
+
+/// Lower a textual OpenAI completion into text-only internal requests.
+pub(crate) fn lower_text_completion_request(
+    config: &RendererConfig,
+    request: &CompletionRequest,
+) -> Result<(String, Vec<TextRequestGroup>), RendererError> {
+    // Accepted OpenAI request attribution does not affect generation.
+    let _ = &request.user;
+    reject_unsupported_fields(&request.unsupported_fields)?;
+    request.extensions.validate()?;
+    let prompts = text_completion_prompts(&request.prompt)?;
+    let prompt_count = prompts.len();
+    let (mut sampling, n, _) = completion_lowering_context(config, request, prompt_count)?;
+    request.sampling_overrides.clone().apply(&mut sampling);
+    let response_id = request.extensions.response_id("cmpl");
+    let mut contexts = request
+        .extensions
+        .clone()
+        .expand(request.model.clone(), prompt_count, n, &response_id)?
+        .into_iter();
+    let mut requests = Vec::with_capacity(prompt_count);
+    for prompt in prompts {
+        let mut choices = Vec::with_capacity(n);
+        for _ in 0..n {
+            let context = contexts
+                .next()
+                .expect("metadata expansion matches completion choice count");
+            choices.push(GenerateRequestIdentity {
+                rid: context.request_id,
+                metadata: context.metadata,
+            });
+        }
+        requests.push(TextRequestGroup {
+            prompt: dynamo_renderer::RenderedPrompt::text(prompt),
+            add_special_tokens: true,
+            options: completion_generation_options(request, sampling.clone()),
+            requests: choices,
+        });
+    }
+    Ok((response_id, requests))
+}
+
+/// Lower a pre-tokenized OpenAI completion directly into token-ID requests.
+pub(crate) fn lower_token_ids_completion_request(
+    config: &RendererConfig,
+    request: &CompletionRequest,
+) -> Result<(String, Vec<TokenIdsRequest>), RendererError> {
+    // Accepted OpenAI request attribution does not affect generation.
+    let _ = &request.user;
+    reject_unsupported_fields(&request.unsupported_fields)?;
+    request.extensions.validate()?;
+    let prompts = token_ids_completion_prompts(&request.prompt)?;
+    let prompt_count = prompts.len();
+    let (mut sampling, n, choice_count) =
+        completion_lowering_context(config, request, prompt_count)?;
+    request.sampling_overrides.clone().apply(&mut sampling);
+    let response_id = request.extensions.response_id("cmpl");
+    let mut contexts = request
+        .extensions
+        .clone()
+        .expand(request.model.clone(), prompt_count, n, &response_id)?
+        .into_iter();
+    let mut requests = Vec::with_capacity(choice_count);
+    for input_ids in prompts {
+        for _ in 0..n {
+            let context = contexts
+                .next()
+                .expect("metadata expansion matches completion choice count");
+            requests.push(
+                TokenIdsRequest::new(
+                    context.request_id,
+                    input_ids.clone(),
+                    completion_generation_options(request, sampling.clone()),
+                )
+                .with_metadata(context.metadata),
+            );
+        }
+    }
+    Ok((response_id, requests))
+}
+
+fn completion_lowering_context(
+    config: &RendererConfig,
+    request: &CompletionRequest,
+    prompt_count: usize,
+) -> Result<(SamplingParams, usize, usize), RendererError> {
+    if request.model != config.served_model_name {
+        return Err(format!("The model `{}` does not exist", request.model).into());
+    }
+    if request.prompt_embeds.is_some() {
+        return Err("prompt_embeds is not supported by the Rust frontend".into());
+    }
+    if request.suffix.is_some() {
+        return Err("suffix is not supported by this model".into());
+    }
+    if request.best_of.is_some_and(|best_of| best_of != 1) {
+        return Err("best_of values greater than 1 are not supported".into());
+    }
+    if request.max_tokens == Some(0) {
+        return Err("max_tokens must be positive".into());
+    }
+    if request.n == Some(0) {
+        return Err("n must be at least 1".into());
+    }
+    let sampling = completion_sampling_params(request, &config.default_sampling_params)?;
+    let n = request.n.unwrap_or(1) as usize;
+    let choice_count = prompt_count
+        .checked_mul(n)
+        .filter(|&count| count <= MAX_OPENAI_CHOICES)
+        .ok_or_else(|| {
+            format!("prompt count times n exceeds the maximum of {MAX_OPENAI_CHOICES}")
+        })?;
+    Ok((sampling, n, choice_count))
+}
+
+fn completion_generation_options(
+    request: &CompletionRequest,
+    sampling_params: SamplingParams,
+) -> GenerationOptions {
+    GenerationOptions {
+        sampling_params,
+        stream: request.stream.unwrap_or(false),
+        return_logprob: request.logprobs.is_some(),
+        logprob_start_len: if request.echo.unwrap_or(false) && request.logprobs.is_some() {
+            0
+        } else {
+            -1
+        },
+        top_logprobs_num: request.logprobs.unwrap_or(0) as i64,
+        return_text_in_logprobs: request.logprobs.map(|_| true),
+        ..Default::default()
+    }
+}
+
+pub fn text_completion_prompts(prompt: &Prompt) -> Result<Vec<String>, String> {
+    match prompt {
+        Prompt::String(text) => {
+            if text.is_empty() {
+                return Err("Prompt cannot be empty".into());
+            }
+            Ok(vec![text.clone()])
+        }
+        Prompt::StringArray(texts) => {
+            if texts.is_empty() || texts.iter().any(String::is_empty) {
+                return Err("Prompt cannot be empty".into());
+            }
+            Ok(texts.clone())
+        }
+        Prompt::IntegerArray(_) | Prompt::ArrayOfIntegerArray(_) => {
+            Err("text completion lowerer requires a text prompt".into())
+        }
+    }
+}
+
+pub fn token_ids_completion_prompts(prompt: &Prompt) -> Result<Vec<TokenIds>, String> {
+    match prompt {
+        Prompt::IntegerArray(ids) => Ok(vec![token_prompt_ids(ids)?]),
+        Prompt::ArrayOfIntegerArray(prompts) => {
+            if prompts.is_empty() {
+                return Err("Prompt cannot be empty".into());
+            }
+            prompts.iter().map(|ids| token_prompt_ids(ids)).collect()
+        }
+        Prompt::String(_) | Prompt::StringArray(_) => {
+            Err("token-ID completion lowerer requires a token-ID prompt".into())
+        }
+    }
+}
+
+fn token_prompt_ids(ids: &[u32]) -> Result<TokenIds, String> {
+    if ids.is_empty() {
+        return Err("Prompt cannot be empty".into());
+    }
+    let input_ids = ids
+        .iter()
+        .map(|&id| i32::try_from(id).map_err(|_| format!("Token ID {id} is out of range")))
+        .collect::<Result<Vec<_>, _>>()?;
+    Ok(input_ids)
+}
+
+pub fn completion_sampling_params(
+    request: &CompletionRequest,
+    model_defaults: &SamplingDefaults,
+) -> Result<SamplingParams, String> {
+    let defaults = sampling_params_with_model_defaults(model_defaults);
+    let mut stop = None;
+    let mut stop_token_ids = None;
+    match request.stop.as_ref() {
+        Some(Stop::String(value)) => stop = Some(OneOrMany::One(value.clone())),
+        Some(Stop::StringArray(values)) => stop = Some(OneOrMany::Many(values.clone())),
+        Some(Stop::TokenIdArray(values)) => {
+            stop_token_ids
+                .get_or_insert_with(Vec::new)
+                .extend(values.iter().map(|&id| id as i64));
+        }
+        None => {}
+    }
+
+    let mut logit_bias = BTreeMap::new();
+    if let Some(values) = request.logit_bias.as_ref() {
+        for (token, bias) in values {
+            let bias = bias
+                .as_f64()
+                .ok_or_else(|| format!("logit_bias[{token:?}] must be a number"))?;
+            logit_bias.insert(token.clone(), bias);
+        }
+    }
+
+    Ok(SamplingParams {
+        max_new_tokens: Some(request.max_tokens.unwrap_or(16) as i64),
+        stop,
+        stop_token_ids,
+        temperature: request
+            .temperature
+            .map(f64::from)
+            .unwrap_or(defaults.temperature),
+        top_p: request.top_p.map(f64::from).unwrap_or(defaults.top_p),
+        frequency_penalty: request.frequency_penalty.unwrap_or(0.0) as f64,
+        presence_penalty: request.presence_penalty.unwrap_or(0.0) as f64,
+        // OpenAI `n` is implemented by fan-out: every native request has one
+        // output, avoiding the native path's intentional `n > 1` rejection.
+        n: 1,
+        logit_bias: (!logit_bias.is_empty()).then_some(logit_bias),
+        sampling_seed: request.seed,
+        ..defaults
+    })
+}

rust/sglang-renderer/src/openai/render.rs

@@ -0,0 +1,29 @@
+//! OpenAI render-only operations, without model execution or HTTP framing.
+
+use super::protocol::{ChatCompletionRequest, CompletionRequest};
+use crate::{GenerateRequest, RendererService, ResponseError};
+
+pub(crate) async fn render_chat(
+    renderer: &RendererService,
+    request: ChatCompletionRequest,
+) -> Result<GenerateRequest, ResponseError> {
+    if request.n.is_some_and(|n| n > 1) {
+        return Err(ResponseError {
+            kind: crate::ResponseErrorKind::InvalidRequest,
+            message: "the standalone chat renderer currently requires n=1".into(),
+        });
+    }
+    let (_, mut chat) = super::chat::prepare_request(renderer, request).await?;
+    Ok(chat
+        .requests
+        .pop()
+        .expect("chat generation contains one request"))
+}
+
+pub(crate) async fn render_completions(
+    renderer: &RendererService,
+    request: CompletionRequest,
+) -> Result<Vec<GenerateRequest>, ResponseError> {
+    let (_, requests) = super::completions::prepare_request(renderer, &request).await?;
+    Ok(requests)
+}

rust/sglang-renderer/src/openai/test_utils.rs

@@ -0,0 +1,94 @@
+use crate::{RendererConfig, RendererLimits, SamplingDefaults};
+use futures::StreamExt;
+use tokio::sync::mpsc;
+
+use crate::{
+    GenerationFinishReason, GenerationOutput, GenerationStream, MatchedStop, ResponseError,
+};
+
+use super::completions::SubmittedChoice;
+
+fn submission() -> (
+    GenerationStream,
+    mpsc::Sender<Result<GenerationOutput, ResponseError>>,
+) {
+    let (tx, rx) = mpsc::channel::<Result<GenerationOutput, ResponseError>>(8);
+    let events = futures::stream::unfold((rx, false), |(mut rx, finished)| async move {
+        if finished {
+            return None;
+        }
+        rx.recv().await.map(|item| {
+            let finished = match &item {
+                Ok(output) => output.finish_reason.is_some(),
+                Err(_) => true,
+            };
+            (item, (rx, finished))
+        })
+    })
+    .boxed();
+    (events, tx)
+}
+
+pub(super) fn chat_submitted(
+    index: usize,
+) -> (
+    (usize, GenerationStream),
+    mpsc::Sender<Result<GenerationOutput, ResponseError>>,
+) {
+    let (events, tx) = submission();
+    ((index, events), tx)
+}
+
+pub(super) fn submitted(
+    index: usize,
+    prompt_index: usize,
+) -> (
+    SubmittedChoice,
+    mpsc::Sender<Result<GenerationOutput, ResponseError>>,
+) {
+    let (events, tx) = submission();
+    (
+        SubmittedChoice {
+            index,
+            prompt_index,
+            echo: String::new(),
+            events,
+        },
+        tx,
+    )
+}
+
+pub(super) fn chunk(text: &str, done: bool) -> Result<GenerationOutput, ResponseError> {
+    let output = GenerationOutput {
+        text: text.to_owned(),
+        token_ids: vec![1],
+        finish_reason: done
+            .then(|| GenerationFinishReason::Stop(Some(MatchedStop::Text("</s>".into())))),
+        prompt_tokens: 5,
+        completion_tokens: 1,
+        extras: None,
+    };
+    Ok(output)
+}
+
+pub(crate) fn renderer_config() -> RendererConfig {
+    RendererConfig {
+        served_model_name: "model".into(),
+        tokenizer_path: ".".into(),
+        revision: None,
+        model_path: String::new(),
+        chat_template: Some("chatml".into()),
+        tool_call_parser: None,
+        reasoning_parser: None,
+        default_chat_template_kwargs: Default::default(),
+        stream_response_default_include_usage: false,
+        default_sampling_params: SamplingDefaults::default(),
+        limits: RendererLimits {
+            vocab_size: 128,
+            context_len: 128,
+            num_reserved_tokens: 0,
+            allow_auto_truncate: false,
+            enable_return_hidden_states: false,
+        },
+    }
+}

rust/sglang-renderer/src/openai/tests.rs

@@ -0,0 +1,429 @@
+//! Protocol preparation invariants shared by rendering and inference.
+
+use super::protocol::{
+    ChatCompletionRequest, CompletionRequest, lower_chat_request, lower_text_completion_request,
+    lower_token_ids_completion_request,
+};
+use super::test_utils::renderer_config;
+use crate::SamplingDefaults;
+
+#[test]
+fn chat_lowering_preserves_template_controls_and_metadata() {
+    let request: ChatCompletionRequest = serde_json::from_value(serde_json::json!({
+        "model": "model",
+        "messages": [{"role": "user", "content": "hello"}],
+        "rid": "chat-lowering",
+        "chat_template_kwargs": {"enable_thinking": false},
+        "continue_final_message": true,
+        "top_k": 17,
+        "min_p": 0.2,
+        "min_tokens": 3,
+        "stop_regex": "END[0-9]",
+        "ignore_eos": true,
+        "skip_special_tokens": false,
+        "return_meta_info": false,
+        "bootstrap_host": "prefill",
+        "bootstrap_port": 8998,
+        "bootstrap_room": 42
+    }))
+    .unwrap();
+
+    assert_eq!(request.model, "model");
+    assert_eq!(
+        request
+            .chat_template_kwargs
+            .as_ref()
+            .and_then(|args| args.get("enable_thinking")),
+        Some(&serde_json::Value::Bool(false))
+    );
+    assert!(request.continue_final_message);
+    assert_eq!(request.sampling_overrides.top_k, Some(17));
+    assert_eq!(request.sampling_overrides.min_p, Some(0.2));
+    assert_eq!(request.sampling_overrides.min_tokens, Some(3));
+    assert_eq!(request.sampling_overrides.ignore_eos, Some(true));
+    assert_eq!(request.sampling_overrides.skip_special_tokens, Some(false));
+    assert_eq!(request.extensions.return_meta_info, Some(false));
+
+    let (response_id, request) = lower_chat_request(&renderer_config(), request).unwrap();
+
+    assert_eq!(response_id, "chat-lowering");
+    assert_eq!(request.metadata.bootstrap_host.as_deref(), Some("prefill"));
+    assert_eq!(request.metadata.bootstrap_port, Some(8998));
+    assert_eq!(request.metadata.bootstrap_room, Some(42));
+    assert_eq!(request.sampling_params.top_k, 17);
+}
+
+#[test]
+fn chat_lowering_rejects_return_meta_info_until_supported() {
+    let request: ChatCompletionRequest = serde_json::from_value(serde_json::json!({
+        "model": "model",
+        "messages": [{"role": "user", "content": "hello"}],
+        "return_meta_info": true
+    }))
+    .unwrap();
+
+    let error = match lower_chat_request(&renderer_config(), request) {
+        Ok(_) => panic!("return_meta_info=true must not be silently ignored"),
+        Err(error) => error,
+    };
+    assert!(error.to_string().contains("return_meta_info"));
+}
+
+#[test]
+fn completion_sampling_defaults_follow_request_model_terminal_priority() {
+    let mut config = renderer_config();
+    config.default_sampling_params = SamplingDefaults {
+        temperature: Some(0.6),
+        top_p: Some(0.9),
+        top_k: Some(32),
+        min_p: Some(0.1),
+        repetition_penalty: Some(1.1),
+    };
+    let omitted: CompletionRequest = serde_json::from_value(serde_json::json!({
+        "model": "model",
+        "prompt": "hello"
+    }))
+    .unwrap();
+    let (_, requests) = lower_text_completion_request(&config, &omitted).unwrap();
+    let sampling = &requests[0].options.sampling_params;
+    assert_eq!(sampling.temperature, 0.6);
+    assert_eq!(sampling.top_p, 0.9);
+    assert_eq!(sampling.top_k, 32);
+    assert_eq!(sampling.min_p, 0.1);
+    assert_eq!(sampling.repetition_penalty, 1.1);
+
+    let explicit: CompletionRequest = serde_json::from_value(serde_json::json!({
+        "model": "model",
+        "prompt": "hello",
+        "temperature": 0.2,
+        "top_p": 0.5,
+        "top_k": 17,
+        "min_p": 0.2,
+        "repetition_penalty": 1.2
+    }))
+    .unwrap();
+    let (_, requests) = lower_text_completion_request(&config, &explicit).unwrap();
+    let sampling = &requests[0].options.sampling_params;
+    assert!((sampling.temperature - 0.2).abs() < 1e-6);
+    assert!((sampling.top_p - 0.5).abs() < 1e-6);
+    assert_eq!(sampling.top_k, 17);
+    assert_eq!(sampling.min_p, 0.2);
+    assert_eq!(sampling.repetition_penalty, 1.2);
+}
+
+#[test]
+fn unsupported_sglang_fields_are_rejected_instead_of_ignored() {
+    let request: ChatCompletionRequest = serde_json::from_value(serde_json::json!({
+        "model": "model",
+        "messages": [{"role": "user", "content": "hello"}],
+        "input_ids": [1, 2, 3],
+        "task": "domain"
+    }))
+    .unwrap();
+
+    let error = lower_chat_request(&renderer_config(), request)
+        .unwrap_err()
+        .to_string();
+
+    assert_eq!(error, "unsupported request fields: input_ids, task");
+}
+
+#[test]
+fn chat_modalities_keep_the_typed_openai_contract() {
+    for modalities in [serde_json::json!("text"), serde_json::json!(["vision"])] {
+        let request = serde_json::json!({
+            "model": "model",
+            "messages": [{"role": "user", "content": "hello"}],
+            "modalities": modalities
+        });
+        assert!(serde_json::from_value::<ChatCompletionRequest>(request).is_err());
+    }
+
+    let text_request: ChatCompletionRequest = serde_json::from_value(serde_json::json!({
+        "model": "model",
+        "messages": [{"role": "user", "content": "hello"}],
+        "modalities": ["text"]
+    }))
+    .unwrap();
+    lower_chat_request(&renderer_config(), text_request).unwrap();
+}
+
+#[test]
+fn reasoning_inputs_normalize_with_python_precedence() {
+    let request: ChatCompletionRequest = serde_json::from_value(serde_json::json!({
+        "model": "model",
+        "messages": [{"role": "user", "content": "hello"}],
+        "reasoning_effort": "high",
+        "reasoning": {"effort": "none", "enabled": true},
+        "chat_template_kwargs": {"thinking": true}
+    }))
+    .unwrap();
+    let (_, request) = lower_chat_request(&renderer_config(), request).unwrap();
+    let args = request.chat_template_args.unwrap();
+
+    assert_eq!(
+        serde_json::to_value(request.reasoning_effort).unwrap(),
+        serde_json::json!("none")
+    );
+    assert_eq!(args.get("thinking"), Some(&serde_json::json!(true)));
+    assert_eq!(args.get("enable_thinking"), Some(&serde_json::json!(false)));
+
+    let request: ChatCompletionRequest = serde_json::from_value(serde_json::json!({
+        "model": "model",
+        "messages": [{"role": "user", "content": "hello"}],
+        "reasoning_effort": "0.5"
+    }))
+    .unwrap();
+    let (_, request) = lower_chat_request(&renderer_config(), request).unwrap();
+    assert_eq!(
+        serde_json::to_value(request.reasoning_effort).unwrap(),
+        serde_json::json!(0.5)
+    );
+    assert_eq!(
+        request
+            .chat_template_args
+            .as_ref()
+            .and_then(|args| args.get("thinking")),
+        Some(&serde_json::json!(true))
+    );
+
+    for invalid in [serde_json::json!(true), serde_json::json!(1.0)] {
+        let request = serde_json::json!({
+            "model": "model",
+            "messages": [{"role": "user", "content": "hello"}],
+            "reasoning_effort": invalid
+        });
+        assert!(serde_json::from_value::<ChatCompletionRequest>(request).is_err());
+    }
+}
+
+#[test]
+fn text_completion_lowering_attaches_batched_metadata_in_prompt_major_order() {
+    let request: CompletionRequest = serde_json::from_value(serde_json::json!({
+        "model": "model",
+        "prompt": ["one", "two"],
+        "n": 2,
+        "rid": ["prompt-a", "prompt-b"],
+        "cache_salt": ["tenant-a", "tenant-b"],
+        "extra_key": ["", "batch"],
+        "bootstrap_host": ["prefill-a", "prefill-b"],
+        "bootstrap_port": [8998, null],
+        "bootstrap_room": [41, 52],
+        "priority": 7,
+        "routed_dp_rank": 2
+    }))
+    .unwrap();
+    let (response_id, requests) =
+        lower_text_completion_request(&renderer_config(), &request).unwrap();
+
+    assert_eq!(response_id, "prompt-a");
+    assert_eq!(
+        requests
+            .iter()
+            .flat_map(|request| request.requests.iter())
+            .map(|request| request.rid.as_str())
+            .collect::<Vec<_>>(),
+        ["prompt-a-0", "prompt-a-1", "prompt-b-0", "prompt-b-1"]
+    );
+    assert_eq!(
+        requests[0].requests[0].metadata.cache_salt.as_deref(),
+        Some("tenant-a")
+    );
+    assert_eq!(requests[0].requests[1].metadata.extra_key, None);
+    assert_eq!(
+        requests[1].requests[0].metadata.extra_key.as_deref(),
+        Some("batch")
+    );
+    assert_eq!(requests[0].requests[0].metadata.bootstrap_port, Some(8998));
+    assert_eq!(requests[1].requests[0].metadata.bootstrap_port, None);
+    assert_eq!(requests[0].requests[1].metadata.bootstrap_room, Some(41));
+    assert_eq!(requests[1].requests[1].metadata.bootstrap_room, Some(52));
+    assert_eq!(requests[1].requests[1].metadata.routed_dp_rank, Some(2));
+}
+
+#[test]
+fn completion_lowering_validates_metadata_lengths_duplicates_and_scalar_rooms() {
+    let request: CompletionRequest = serde_json::from_value(serde_json::json!({
+        "model": "model",
+        "prompt": ["one", "two"],
+        "rid": ["duplicate", "duplicate"],
+        "cache_salt": ["only-one"]
+    }))
+    .unwrap();
+    let error = lower_text_completion_request(&renderer_config(), &request).unwrap_err();
+    assert!(error.to_string().contains("duplicate request ID"));
+
+    let request: CompletionRequest = serde_json::from_value(serde_json::json!({
+        "model": "model",
+        "prompt": ["one", "two"],
+        "cache_salt": ["only-one"]
+    }))
+    .unwrap();
+    let error = lower_text_completion_request(&renderer_config(), &request).unwrap_err();
+    assert!(error.to_string().contains("prompt batch size (2)"));
+
+    let request: CompletionRequest = serde_json::from_value(serde_json::json!({
+        "model": "model",
+        "prompt": ["one", "two"],
+        "n": 2,
+        "bootstrap_room": 90
+    }))
+    .unwrap();
+    let (_, requests) = lower_text_completion_request(&renderer_config(), &request).unwrap();
+    assert_eq!(
+        requests
+            .iter()
+            .flat_map(|request| request.requests.iter())
+            .map(|request| request.metadata.bootstrap_room)
+            .collect::<Vec<_>>(),
+        [Some(90), Some(90), Some(91), Some(91)]
+    );
+}
+
+#[test]
+fn completion_lowering_rejects_zero_max_tokens() {
+    let request: CompletionRequest = serde_json::from_value(serde_json::json!({
+        "model": "model",
+        "prompt": "hello",
+        "max_tokens": 0
+    }))
+    .unwrap();
+
+    let error = lower_text_completion_request(&renderer_config(), &request).unwrap_err();
+
+    assert_eq!(error.to_string(), "max_tokens must be positive");
+}
+
+#[test]
+fn token_id_completion_lowering_attaches_batched_metadata() {
+    let request: CompletionRequest = serde_json::from_value(serde_json::json!({
+        "model": "model",
+        "prompt": [[1, 2], [3]],
+        "n": 2,
+        "rid": ["tokens-a", "tokens-b"],
+        "bootstrap_host": ["prefill-a", "prefill-b"],
+        "bootstrap_port": [8998, 8999],
+        "bootstrap_room": [41, 52]
+    }))
+    .unwrap();
+    let (response_id, requests) =
+        lower_token_ids_completion_request(&renderer_config(), &request).unwrap();
+
+    assert_eq!(response_id, "tokens-a");
+    assert_eq!(requests[2].rid, "tokens-b-0");
+    assert_eq!(requests[2].input_ids, [3]);
+    assert_eq!(
+        requests[2].metadata.bootstrap_host.as_deref(),
+        Some("prefill-b")
+    );
+    assert_eq!(requests[2].metadata.bootstrap_port, Some(8999));
+    assert_eq!(requests[3].metadata.bootstrap_room, Some(52));
+}
+
+#[tokio::test]
+async fn route_operations_decode_tokens_without_http() {
+    use super::{OpenAIService, OperationResponse};
+    use crate::engine::{
+        GenerateTransport, GenerationService, TokenDecoder, TokenDelta, TokenStream,
+    };
+    use crate::{
+        DynamoTokenizer, GenerateRequest, GenerationFinishReason, RendererService, ResponseError,
+    };
+    use futures::{StreamExt, future::BoxFuture};
+    use std::sync::{Arc, Mutex};
+
+    struct MemoryTransport(Mutex<Vec<GenerateRequest>>);
+    impl GenerateTransport for MemoryTransport {
+        fn generate(
+            &self,
+            request: GenerateRequest,
+        ) -> BoxFuture<'_, Result<TokenStream, ResponseError>> {
+            Box::pin(async move {
+                self.0.lock().unwrap().push(request);
+                Ok(futures::stream::iter([Ok(TokenDelta {
+                    token_ids: vec![104],
+                    prompt_tokens: 5,
+                    completion_tokens: 1,
+                    finish_reason: Some(GenerationFinishReason::Length),
+                    ..Default::default()
+                })])
+                .boxed())
+            })
+        }
+    }
+    async fn values<U: serde::Serialize, C: serde::Serialize>(
+        result: OperationResponse<U, C>,
+    ) -> Vec<serde_json::Value> {
+        match result {
+            OperationResponse::Unary(value) => vec![serde_json::to_value(value).unwrap()],
+            OperationResponse::Stream(stream) => {
+                stream
+                    .map(|value| serde_json::to_value(value.unwrap()).unwrap())
+                    .collect()
+                    .await
+            }
+        }
+    }
+
+    let tokenizer = crate::engine::test_utils::tiny_tokenizer();
+    let prompt_ids = tokenizer.encode("hello").unwrap().token_ids().to_vec();
+    let transport = Arc::new(MemoryTransport(Mutex::new(Vec::new())));
+    let renderer = Arc::new(RendererService::with_tokenizer(
+        renderer_config(),
+        Arc::new(DynamoTokenizer::new(tokenizer.clone(), tokenizer.clone())),
+        1,
+        1,
+    ));
+    let service = OpenAIService::new(
+        renderer,
+        GenerationService::new(transport.clone(), TokenDecoder::new(tokenizer)),
+    );
+    for chat in [false, true] {
+        for stream in [false, true] {
+            let mut body =
+                serde_json::json!({"model": "model", "n": 2, "max_tokens": 4, "stream": stream});
+            let responses = if chat {
+                body["messages"] = serde_json::json!([{"role": "user", "content": "hello"}]);
+                values(
+                    service
+                        .chat(serde_json::from_value(body).unwrap())
+                        .await
+                        .unwrap(),
+                )
+                .await
+            } else {
+                body["prompt"] = serde_json::json!(prompt_ids);
+                body["echo"] = serde_json::json!(true);
+                values(
+                    service
+                        .complete(serde_json::from_value(body).unwrap())
+                        .await
+                        .unwrap(),
+                )
+                .await
+            };
+            let mut texts = [String::new(), String::new()];
+            let mut finished = [false; 2];
+            for response in responses {
+                for choice in response["choices"].as_array().unwrap() {
+                    let index = choice["index"].as_u64().unwrap() as usize;
+                    let text = if chat {
+                        &choice[if stream { "delta" } else { "message" }]["content"]
+                    } else {
+                        &choice["text"]
+                    };
+                    texts[index].push_str(text.as_str().unwrap_or_default());
+                    if let Some(reason) = choice["finish_reason"].as_str() {
+                        assert_eq!(reason, "length");
+                        finished[index] = true;
+                    }
+                }
+            }
+            assert_eq!(texts, [if chat { "h" } else { "helloh" }; 2]);
+            assert_eq!(finished, [true; 2]);
+        }
+    }
+    let requests = transport.0.lock().unwrap();
+    assert_eq!(requests.len(), 8);
+    assert!(requests.iter().all(|request| !request.input_ids.is_empty()));
+}

rust/sglang-renderer/src/openai/tokenize.rs

@@ -0,0 +1,149 @@
+//! SGLang-compatible prompt and chat tokenization.
+
+use dynamo_protocols::types::{
+    ChatCompletionRequestMessage, ChatCompletionTool, ChatCompletionToolChoiceOption,
+};
+use futures::future::try_join_all;
+use serde::Deserialize;
+use serde_json::{Value, json};
+
+use crate::{ChatRequest, OneOrMany, ReasoningEffort, RendererService, ResponseError};
+
+use super::protocol::normalize_reasoning_inputs;
+
+pub(crate) async fn tokenize(
+    renderer: &RendererService,
+    mut request: TokenizeRequest,
+) -> Result<Value, ResponseError> {
+    let has_prompt = request.prompt.is_some();
+    let has_messages = request.messages.is_some();
+    if has_prompt == has_messages {
+        return Err(ResponseError {
+            kind: crate::ResponseErrorKind::InvalidRequest,
+            message: "Exactly one of 'prompt' or 'messages' must be provided.".into(),
+        });
+    }
+    let (tokens, count) = match request.prompt.take() {
+        Some(prompt) => {
+            let add_special_tokens = request.add_special_tokens;
+            match prompt {
+                OneOrMany::One(text) => {
+                    let tokens = renderer.tokenize_prompt(text, add_special_tokens).await?;
+                    (json!(tokens), json!(tokens.len()))
+                }
+                OneOrMany::Many(texts) => {
+                    let tokens = try_join_all(
+                        texts
+                            .into_iter()
+                            .map(|text| renderer.tokenize_prompt(text, add_special_tokens)),
+                    )
+                    .await?;
+                    let count = tokens.iter().map(Vec::len).collect::<Vec<_>>();
+                    (json!(tokens), json!(count))
+                }
+            }
+        }
+        None => {
+            let request = request.into_chat(&renderer.config().served_model_name)?;
+            let tokens = renderer.tokenize_chat(request).await?;
+            (json!(tokens), json!(tokens.len()))
+        }
+    };
+    Ok(json!({
+        "tokens": tokens,
+        "count": count,
+        "max_model_len": renderer.config().limits.context_len,
+    }))
+}
+
+#[derive(Deserialize)]
+pub(crate) struct TokenizeRequest {
+    #[serde(default)]
+    prompt: Option<OneOrMany<String>>,
+    #[serde(default)]
+    messages: Option<Vec<ChatCompletionRequestMessage>>,
+    #[serde(default = "default_true")]
+    add_special_tokens: bool,
+    #[serde(default)]
+    model: Option<String>,
+    #[serde(default)]
+    tools: Option<Vec<ChatCompletionTool>>,
+    #[serde(default)]
+    tool_choice: Option<ChatCompletionToolChoiceOption>,
+    #[serde(default)]
+    reasoning_effort: Option<ReasoningEffort>,
+    #[serde(default)]
+    reasoning: Option<Value>,
+    #[serde(default)]
+    continue_final_message: bool,
+    #[serde(default)]
+    chat_template_kwargs: Option<std::collections::HashMap<String, Value>>,
+}
+
+impl TokenizeRequest {
+    fn into_chat(mut self, served_model: &str) -> Result<ChatRequest, crate::RendererError> {
+        normalize_reasoning_inputs(
+            &mut self.reasoning_effort,
+            self.reasoning.take(),
+            &mut self.chat_template_kwargs,
+        )?;
+        let model = self.model.unwrap_or_else(|| served_model.to_owned());
+        if model != served_model {
+            return Err(format!("The model `{model}` does not exist").into());
+        }
+        Ok(ChatRequest {
+            rid: "tokenize".into(),
+            model,
+            messages: self
+                .messages
+                .take()
+                .expect("chat tokenization request has messages"),
+            tools: self.tools,
+            tool_choice: self.tool_choice,
+            response_format: None,
+            reasoning_effort: self.reasoning_effort,
+            continue_final_message: self.continue_final_message,
+            chat_template_args: self.chat_template_kwargs,
+            sampling_params: Default::default(),
+            choice_count: 1,
+            stream: false,
+            return_logprob: false,
+            top_logprobs_num: 0,
+            parallel_tool_calls: true,
+            metadata: crate::GenerateRequestMetadata::default(),
+        })
+    }
+}
+
+const fn default_true() -> bool {
+    true
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn chat_tokenization_lowers_tokenize_specific_options() {
+        let request: TokenizeRequest = serde_json::from_value(json!({
+            "messages": [{"role": "assistant", "content": "partial"}],
+            "reasoning_effort": "high",
+            "continue_final_message": true,
+            "chat_template_kwargs": {"marker": true}
+        }))
+        .unwrap();
+
+        let chat = request.into_chat("model").unwrap();
+
+        assert!(chat.continue_final_message);
+        assert_eq!(
+            chat.chat_template_args
+                .as_ref()
+                .and_then(|args| args.get("marker")),
+            Some(&json!(true))
+        );
+        assert_eq!(
+            serde_json::to_value(chat.reasoning_effort).unwrap(),
+            json!("high")
+        );
+    }
+}

rust/sglang-renderer/src/postprocessing/mod.rs

@@ -0,0 +1,774 @@
+//! Request-scoped OpenAI chat output interpretation.
+//!
+//! The processor owns parser selection and mutable reasoning/tool state. Its
+//! input is decoded engine output; its output is typed chat semantics.
+//! Submission, cancellation, and scheduler transport remain host
+//! responsibilities. HTTP and future gRPC adapters consume these semantic
+//! events without reimplementing parser behavior.
+
+use std::pin::Pin;
+
+use dynamo_parsers::ToolDefinition;
+use dynamo_parsers::reasoning::{
+    ReasoningParser as _, ReasoningParserType, ReasoningParserWrapper,
+};
+use dynamo_parsers::tool_calling::jail::{Annotated, apply_tool_calling_jail};
+use dynamo_protocols::types::{
+    ChatChoiceLogprobs, ChatChoiceStream, ChatCompletionMessageContent,
+    ChatCompletionMessageToolCallChunk, ChatCompletionStreamResponseDelta,
+    ChatCompletionToolChoiceOption, CreateChatCompletionStreamResponse, FinishReason, Role,
+};
+use futures::{Stream, StreamExt};
+
+use crate::ResponseError;
+use crate::preprocessing::dynamo_parser_name;
+
+/// Engine-neutral terminal reason understood by chat response processing.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ChatFinishReason {
+    Stop,
+    Length,
+    ContentFilter,
+    ToolCalls,
+}
+
+/// One decoded engine update after host-specific egress conversion.
+pub struct DecodedChatEvent {
+    pub choice: usize,
+    pub text: String,
+    pub token_ids: Vec<i32>,
+    pub finish_reason: Option<ChatFinishReason>,
+    pub logprobs: Option<ChatChoiceLogprobs>,
+    pub prompt_tokens: u32,
+    pub completion_tokens: u64,
+}
+
+/// One semantic tool-call delta, independent of HTTP or gRPC framing.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ChatToolCallDelta {
+    pub index: u32,
+    pub id: Option<String>,
+    pub name: Option<String>,
+    pub arguments: Option<String>,
+}
+
+/// Semantic chat output. Protocol adapters add response metadata and wire
+/// framing without knowing how reasoning or tool syntax was parsed.
+#[derive(Debug, Clone)]
+pub enum ChatEvent {
+    Role {
+        choice: usize,
+    },
+    Delta {
+        choice: usize,
+        content: Option<String>,
+        reasoning_content: Option<String>,
+        tool_calls: Option<Vec<ChatToolCallDelta>>,
+        finish_reason: Option<ChatFinishReason>,
+        logprobs: Option<ChatChoiceLogprobs>,
+    },
+    Usage {
+        prompt_tokens: u32,
+        completion_tokens: u64,
+    },
+}
+
+/// Mutable parser state for one generated choice.
+struct ChoiceResponseProcessor {
+    reasoning: ReasoningStreamSplitter,
+}
+
+/// Request-scoped chat response processor.
+///
+/// Parser names, tool definitions, structural-tag decisions, and mutable
+/// per-choice state are private so protocol adapters cannot accidentally
+/// reimplement the semantic contract.
+pub struct ChatResponseProcessor {
+    tool_parser: Option<String>,
+    tools: Option<Vec<ToolDefinition>>,
+    tool_choice: Option<ChatCompletionToolChoiceOption>,
+    uses_tool_call_structural_tag: bool,
+    parallel_tool_calls: bool,
+    choices: Vec<ChoiceResponseProcessor>,
+}
+
+impl ChatResponseProcessor {
+    pub(crate) fn new(
+        tool_parser: Option<String>,
+        reasoning_parser: Option<String>,
+        tools: Option<Vec<ToolDefinition>>,
+        tool_choice: Option<ChatCompletionToolChoiceOption>,
+        uses_tool_call_structural_tag: bool,
+        parallel_tool_calls: bool,
+        choice_count: usize,
+    ) -> Self {
+        Self {
+            tool_parser,
+            tools,
+            tool_choice,
+            uses_tool_call_structural_tag,
+            parallel_tool_calls,
+            choices: (0..choice_count)
+                .map(|_| ChoiceResponseProcessor {
+                    reasoning: ReasoningStreamSplitter::new(reasoning_parser.as_deref(), None),
+                })
+                .collect(),
+        }
+    }
+
+    pub(crate) fn with_reasoning_state(mut self, reasoning_state: Option<bool>) -> Self {
+        for choice in &mut self.choices {
+            choice.reasoning.initial_reasoning = reasoning_state;
+        }
+        self
+    }
+
+    /// Interpret decoded output and emit semantic chat events.
+    ///
+    /// OpenAI-shaped values are used only as a private adapter to Dynamo's
+    /// stateful tool-call jail. They are removed before events leave this
+    /// crate, so response identity, model metadata, usage policy, and wire
+    /// framing remain outside this semantic processor.
+    pub fn process_stream<S>(
+        mut self,
+        input: S,
+    ) -> Pin<Box<dyn Stream<Item = Result<ChatEvent, ResponseError>> + Send>>
+    where
+        S: Stream<Item = Result<DecodedChatEvent, ResponseError>> + Send + 'static,
+    {
+        let count = self.choices.len();
+        let raw = async_stream::stream! {
+            let mut prompt_tokens = 0u32;
+            let mut completion_tokens = 0u64;
+            let mut role_emitted = vec![false; count];
+
+            futures::pin_mut!(input);
+            while let Some(item) = input.next().await {
+                let decoded = match item {
+                    Ok(decoded) => decoded,
+                    Err(error) => {
+                        yield Annotated {
+                            data: None,
+                            id: None,
+                            event: None,
+                            comment: None,
+                            error: serde_json::to_string(&error).ok(),
+                        };
+                        continue;
+                    }
+                };
+
+                if prompt_tokens == 0 {
+                    prompt_tokens = decoded.prompt_tokens;
+                }
+                completion_tokens = completion_tokens.saturating_add(decoded.completion_tokens);
+
+                if decoded.choice >= count {
+                    yield Annotated {
+                        data: None,
+                        id: None,
+                        event: None,
+                        comment: None,
+                        error: serde_json::to_string(&ResponseError {
+                            kind: crate::ResponseErrorKind::Internal,
+                            message: format!("output choice {} is out of range", decoded.choice),
+                        }).ok(),
+                    };
+                    continue;
+                }
+
+                if !role_emitted[decoded.choice] {
+                    role_emitted[decoded.choice] = true;
+                    yield annotated_choices(vec![ChatChoiceStream {
+                        index: decoded.choice as u32,
+                        delta: chat_delta(None, Some(Role::Assistant), None, None),
+                        finish_reason: None,
+                        logprobs: None,
+                    }]);
+                }
+
+                let choice = &mut self.choices[decoded.choice];
+                let index = decoded.choice as u32;
+                let (reasoning_text, normal_text) =
+                    choice.reasoning.split(&decoded.text, &decoded.token_ids);
+                let mut remaining_logprobs = decoded.logprobs;
+                let mut emitted = Vec::with_capacity(3);
+                if !reasoning_text.is_empty() {
+                    emitted.push(ChatChoiceStream {
+                        index,
+                        delta: chat_delta(None, None, None, Some(reasoning_text)),
+                        finish_reason: None,
+                        logprobs: remaining_logprobs.take(),
+                    });
+                }
+                if !normal_text.is_empty() {
+                    emitted.push(ChatChoiceStream {
+                        index,
+                        delta: chat_delta(Some(normal_text), None, None, None),
+                        finish_reason: None,
+                        logprobs: remaining_logprobs.take(),
+                    });
+                }
+
+                if decoded.finish_reason.is_some() {
+                    let (reasoning_tail, normal_tail) = choice.reasoning.finish();
+                    if !reasoning_tail.is_empty() {
+                        emitted.push(ChatChoiceStream {
+                            index,
+                            delta: chat_delta(None, None, None, Some(reasoning_tail)),
+                            finish_reason: None,
+                            logprobs: None,
+                        });
+                    }
+                    if !normal_tail.is_empty() {
+                        emitted.push(ChatChoiceStream {
+                            index,
+                            delta: chat_delta(Some(normal_tail), None, None, None),
+                            finish_reason: None,
+                            logprobs: None,
+                        });
+                    }
+                }
+
+                let finish_reason = decoded.finish_reason.map(to_dynamo_finish_reason);
+                match emitted.last_mut() {
+                    Some(last) => last.finish_reason = finish_reason,
+                    None => emitted.push(ChatChoiceStream {
+                        index,
+                        delta: chat_delta(None, None, None, None),
+                        finish_reason,
+                        logprobs: remaining_logprobs,
+                    }),
+                }
+                yield annotated_choices(emitted);
+            }
+
+            yield annotated_usage(prompt_tokens, completion_tokens);
+        };
+
+        let post_tool_terminal_markers = self.tool_parser.as_deref().map_or(&[][..], |parser| {
+            match dynamo_parser_name(parser) {
+                "qwen25" => &["<|im_end|>"],
+                "glm47" => &["<|user|>", "<|endoftext|>", "<|observation|>"],
+                _ => &[],
+            }
+        });
+        let parsed: Pin<
+            Box<dyn Stream<Item = Annotated<CreateChatCompletionStreamResponse>> + Send>,
+        > = if let Some(parser) = self.tool_parser {
+            Box::pin(apply_tool_calling_jail(
+                Some(dynamo_parser_name(&parser).to_owned()),
+                self.tool_choice,
+                self.tools,
+                self.uses_tool_call_structural_tag,
+                raw,
+            ))
+        } else {
+            Box::pin(raw)
+        };
+        let parallel_tool_calls = self.parallel_tool_calls;
+
+        Box::pin(async_stream::stream! {
+            let mut tool_calls_seen = vec![false; count];
+            futures::pin_mut!(parsed);
+            while let Some(mut item) = parsed.next().await {
+                if let Some(response) = item.data.take() {
+                    if response.choices.is_empty()
+                        && let Some(usage) = response.usage
+                    {
+                        yield Ok(ChatEvent::Usage {
+                            prompt_tokens: usage.prompt_tokens,
+                            completion_tokens: u64::from(usage.completion_tokens),
+                        });
+                        continue;
+                    }
+                    for choice in response.choices {
+                        let index = choice.index as usize;
+                        let had_tool_calls = tool_calls_seen.get(index).copied().unwrap_or(false);
+                        let mut tool_calls = choice.delta.tool_calls.map(|calls| {
+                            calls.into_iter().map(tool_call_delta).collect::<Vec<_>>()
+                        });
+                        if !parallel_tool_calls
+                            && let Some(calls) = tool_calls.as_mut()
+                        {
+                            if had_tool_calls {
+                                calls.clear();
+                            } else {
+                                calls.truncate(1);
+                            }
+                            if calls.is_empty() {
+                                tool_calls = None;
+                            }
+                        }
+                        let emitted_tool_calls = tool_calls.as_ref().is_some_and(|calls| !calls.is_empty());
+                        if emitted_tool_calls
+                            && let Some(seen) = tool_calls_seen.get_mut(index)
+                        {
+                            *seen = true;
+                        }
+                        let mut content = match choice.delta.content {
+                            Some(ChatCompletionMessageContent::Text(text)) => Some(text),
+                            _ => None,
+                        };
+                        if had_tool_calls
+                            && content.as_ref().is_some_and(|text| {
+                                post_tool_terminal_markers.contains(&text.trim())
+                            })
+                        {
+                            content = None;
+                        }
+                        if choice.delta.role.is_some()
+                            && content.is_none()
+                            && choice.delta.reasoning_content.is_none()
+                            && tool_calls.is_none()
+                            && choice.finish_reason.is_none()
+                        {
+                            yield Ok(ChatEvent::Role { choice: index });
+                            continue;
+                        }
+                        yield Ok(ChatEvent::Delta {
+                            choice: index,
+                            content,
+                            reasoning_content: choice.delta.reasoning_content,
+                            tool_calls,
+                            finish_reason: choice.finish_reason.map(from_dynamo_finish_reason),
+                            logprobs: choice.logprobs,
+                        });
+                    }
+                } else if let Some(error) = item.error {
+                    let error = serde_json::from_str(&error).unwrap_or(ResponseError {
+                        kind: crate::ResponseErrorKind::Internal,
+                        message: error,
+                    });
+                    yield Err(error);
+                }
+            }
+        })
+    }
+}
+
+#[allow(deprecated)]
+fn chat_delta(
+    content: Option<String>,
+    role: Option<Role>,
+    tool_calls: Option<Vec<ChatCompletionMessageToolCallChunk>>,
+    reasoning_content: Option<String>,
+) -> ChatCompletionStreamResponseDelta {
+    ChatCompletionStreamResponseDelta {
+        content: content.map(ChatCompletionMessageContent::Text),
+        function_call: None,
+        tool_calls,
+        role,
+        refusal: None,
+        reasoning_content,
+    }
+}
+
+fn annotated_choices(
+    choices: Vec<ChatChoiceStream>,
+) -> Annotated<CreateChatCompletionStreamResponse> {
+    Annotated {
+        data: Some(CreateChatCompletionStreamResponse {
+            id: String::new(),
+            choices,
+            created: 0,
+            model: String::new(),
+            service_tier: None,
+            system_fingerprint: None,
+            object: String::new(),
+            usage: None,
+        }),
+        id: None,
+        event: None,
+        comment: None,
+        error: None,
+    }
+}
+
+fn annotated_usage(
+    prompt_tokens: u32,
+    completion_tokens: u64,
+) -> Annotated<CreateChatCompletionStreamResponse> {
+    Annotated {
+        data: Some(CreateChatCompletionStreamResponse {
+            id: String::new(),
+            choices: Vec::new(),
+            created: 0,
+            model: String::new(),
+            service_tier: None,
+            system_fingerprint: None,
+            object: String::new(),
+            usage: Some(dynamo_protocols::types::CompletionUsage {
+                prompt_tokens,
+                completion_tokens: u32::try_from(completion_tokens).unwrap_or(u32::MAX),
+                total_tokens: prompt_tokens
+                    .saturating_add(u32::try_from(completion_tokens).unwrap_or(u32::MAX)),
+                prompt_tokens_details: None,
+                completion_tokens_details: None,
+            }),
+        }),
+        id: None,
+        event: None,
+        comment: None,
+        error: None,
+    }
+}
+
+fn tool_call_delta(call: ChatCompletionMessageToolCallChunk) -> ChatToolCallDelta {
+    ChatToolCallDelta {
+        index: call.index,
+        id: call.id,
+        name: call
+            .function
+            .as_ref()
+            .and_then(|function| function.name.clone()),
+        arguments: call.function.and_then(|function| function.arguments),
+    }
+}
+
+fn to_dynamo_finish_reason(reason: ChatFinishReason) -> FinishReason {
+    match reason {
+        ChatFinishReason::Stop => FinishReason::Stop,
+        ChatFinishReason::Length => FinishReason::Length,
+        ChatFinishReason::ContentFilter => FinishReason::ContentFilter,
+        ChatFinishReason::ToolCalls => FinishReason::ToolCalls,
+    }
+}
+
+fn from_dynamo_finish_reason(reason: FinishReason) -> ChatFinishReason {
+    match reason {
+        FinishReason::Stop => ChatFinishReason::Stop,
+        FinishReason::Length => ChatFinishReason::Length,
+        FinishReason::ContentFilter => ChatFinishReason::ContentFilter,
+        FinishReason::ToolCalls | FinishReason::FunctionCall => ChatFinishReason::ToolCalls,
+    }
+}
+
+fn build_reasoning_parser(server_name: &str) -> ReasoningParserWrapper {
+    let name = match server_name {
+        "deepseek-r1" | "step3p5" => "deepseek_r1",
+        "kimi_k2" => "kimi_k25",
+        "gpt-oss" => "gpt_oss",
+        "nemotron_3" => "nemotron3",
+        "interns1" => "qwen3",
+        "qwen3-thinking" | "minimax" => "deepseek_r1",
+        _ => server_name,
+    };
+    ReasoningParserType::get_reasoning_parser_from_name(name)
+}
+
+struct ReasoningStreamSplitter {
+    name: Option<String>,
+    parser: Option<ReasoningParserWrapper>,
+    initial_reasoning: Option<bool>,
+}
+
+impl ReasoningStreamSplitter {
+    fn new(name: Option<&str>, initial_reasoning: Option<bool>) -> Self {
+        Self {
+            name: name.map(str::to_owned),
+            parser: None,
+            initial_reasoning,
+        }
+    }
+
+    fn split(&mut self, text: &str, token_ids: &[i32]) -> (String, String) {
+        let Some(name) = self.name.as_deref() else {
+            return (String::new(), text.to_owned());
+        };
+        let initial_reasoning = self.initial_reasoning;
+        let parser = self.parser.get_or_insert_with(|| {
+            let mut parser = build_reasoning_parser(name);
+            if let Some(initial_reasoning) = initial_reasoning {
+                parser.set_in_reasoning(initial_reasoning);
+            }
+            parser
+        });
+        let token_ids = token_ids
+            .iter()
+            .filter_map(|&id| u32::try_from(id).ok())
+            .collect::<Vec<_>>();
+        let split = parser.parse_reasoning_streaming_incremental(text, &token_ids);
+        (split.reasoning_text, split.normal_text)
+    }
+
+    fn finish(&mut self) -> (String, String) {
+        let Some(parser) = self.parser.as_mut() else {
+            return (String::new(), String::new());
+        };
+        let tail = parser.finish_reasoning_stream();
+        (tail.reasoning_text, tail.normal_text)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use futures::stream;
+
+    fn processor(
+        tool_parser: Option<&str>,
+        reasoning_parser: Option<&str>,
+        choices: usize,
+    ) -> ChatResponseProcessor {
+        ChatResponseProcessor::new(
+            tool_parser.map(str::to_owned),
+            reasoning_parser.map(str::to_owned),
+            None,
+            Some(ChatCompletionToolChoiceOption::Auto),
+            false,
+            true,
+            choices,
+        )
+    }
+
+    fn chunk(choice: usize, text: &str, done: bool) -> Result<DecodedChatEvent, ResponseError> {
+        Ok(DecodedChatEvent {
+            choice,
+            text: text.into(),
+            token_ids: vec![],
+            finish_reason: done.then_some(ChatFinishReason::Stop),
+            logprobs: None,
+            prompt_tokens: 5,
+            completion_tokens: 1,
+        })
+    }
+
+    #[test]
+    fn streaming_processor_emits_semantics_without_wire_metadata() {
+        let events = futures::executor::block_on(
+            processor(None, Some("deepseek-r1"), 1)
+                .process_stream(stream::iter(vec![
+                    chunk(0, "<think>be", false),
+                    chunk(0, "cause</think>Paris", true),
+                ]))
+                .collect::<Vec<_>>(),
+        );
+        let reasoning = events
+            .iter()
+            .filter_map(|event| match event {
+                Ok(ChatEvent::Delta {
+                    reasoning_content: Some(text),
+                    ..
+                }) => Some(text.as_str()),
+                _ => None,
+            })
+            .collect::<String>();
+        assert_eq!(reasoning, "because");
+        assert!(events.iter().any(|event| matches!(
+            event,
+            Ok(ChatEvent::Delta {
+                content: Some(text), ..
+            }) if text == "Paris"
+        )));
+        assert!(matches!(
+            events.last(),
+            Some(Ok(ChatEvent::Usage {
+                prompt_tokens: 5,
+                completion_tokens: 2
+            }))
+        ));
+    }
+
+    #[test]
+    fn each_choice_has_isolated_reasoning_state() {
+        let events = futures::executor::block_on(
+            processor(None, Some("deepseek-r1"), 2)
+                .process_stream(stream::iter(vec![
+                    chunk(0, "<think>zero", false),
+                    chunk(1, "<think>one", false),
+                    chunk(0, "</think>A", true),
+                    chunk(1, "</think>B", true),
+                ]))
+                .collect::<Vec<_>>(),
+        );
+        let deltas = events.iter().filter_map(|event| match event {
+            Ok(ChatEvent::Delta {
+                choice,
+                content: Some(content),
+                ..
+            }) => Some((*choice, content.as_str())),
+            _ => None,
+        });
+        assert_eq!(deltas.collect::<Vec<_>>(), vec![(0, "A"), (1, "B")]);
+        let roles = events.iter().filter_map(|event| match event {
+            Ok(ChatEvent::Role { choice }) => Some(*choice),
+            _ => None,
+        });
+        assert_eq!(roles.collect::<Vec<_>>(), vec![0, 1]);
+    }
+
+    #[test]
+    fn prompt_injected_reasoning_starts_without_opening_marker() {
+        let events = futures::executor::block_on(
+            ChatResponseProcessor::new(
+                None,
+                Some("glm45".into()),
+                None,
+                Some(ChatCompletionToolChoiceOption::Auto),
+                false,
+                true,
+                1,
+            )
+            .with_reasoning_state(Some(true))
+            .process_stream(stream::iter(vec![chunk(
+                0,
+                "reasoning</think>answer",
+                true,
+            )]))
+            .collect::<Vec<_>>(),
+        );
+
+        let reasoning = events
+            .iter()
+            .filter_map(|event| match event {
+                Ok(ChatEvent::Delta {
+                    reasoning_content: Some(text),
+                    ..
+                }) => Some(text.as_str()),
+                _ => None,
+            })
+            .collect::<String>();
+        let content = events
+            .iter()
+            .filter_map(|event| match event {
+                Ok(ChatEvent::Delta {
+                    content: Some(text),
+                    ..
+                }) => Some(text.as_str()),
+                _ => None,
+            })
+            .collect::<String>();
+        assert_eq!(reasoning, "reasoning");
+        assert_eq!(content, "answer");
+    }
+
+    #[test]
+    fn unknown_reasoning_state_preserves_parser_default() {
+        let events = futures::executor::block_on(
+            processor(None, Some("deepseek-r1"), 1)
+                .process_stream(stream::iter(vec![chunk(
+                    0,
+                    "reasoning</think>answer",
+                    true,
+                )]))
+                .collect::<Vec<_>>(),
+        );
+
+        let reasoning = events
+            .iter()
+            .filter_map(|event| match event {
+                Ok(ChatEvent::Delta {
+                    reasoning_content: Some(text),
+                    ..
+                }) => Some(text.as_str()),
+                _ => None,
+            })
+            .collect::<String>();
+        let content = events
+            .iter()
+            .filter_map(|event| match event {
+                Ok(ChatEvent::Delta {
+                    content: Some(text),
+                    ..
+                }) => Some(text.as_str()),
+                _ => None,
+            })
+            .collect::<String>();
+        assert_eq!(reasoning, "reasoning");
+        assert_eq!(content, "answer");
+    }
+
+    #[test]
+    fn qwen_tool_calls_drop_post_call_special_tokens() {
+        let events = futures::executor::block_on(
+            processor(Some("qwen"), None, 1)
+                .process_stream(stream::iter(vec![chunk(
+                    0,
+                    "Let me check.\n<tool_call>\n{\"name\":\"get_weather\",\"arguments\":{\"city\":\"Paris\"}}\n</tool_call><|im_end|>",
+                    true,
+                )]))
+                .collect::<Vec<_>>(),
+        );
+
+        let content = events
+            .iter()
+            .filter_map(|event| match event {
+                Ok(ChatEvent::Delta {
+                    content: Some(text),
+                    ..
+                }) => Some(text.as_str()),
+                _ => None,
+            })
+            .collect::<String>();
+        assert!(content.contains("Let me check."));
+        assert!(!content.contains("<|im_end|>"));
+        assert!(events.iter().any(|event| matches!(
+            event,
+            Ok(ChatEvent::Delta {
+                tool_calls: Some(calls),
+                ..
+            }) if calls.iter().any(|call| call.name.as_deref() == Some("get_weather"))
+        )));
+    }
+
+    #[test]
+    fn qwen_tool_calls_drop_split_terminal_special_tokens() {
+        let events = futures::executor::block_on(
+            processor(Some("qwen25"), None, 1)
+                .process_stream(stream::iter(vec![
+                    chunk(
+                        0,
+                        "<tool_call>\n{\"name\":\"get_weather\",\"arguments\":{}}\n</tool_call>",
+                        false,
+                    ),
+                    chunk(0, "<|im_end|>", true),
+                ]))
+                .collect::<Vec<_>>(),
+        );
+
+        assert!(!events.iter().any(|event| matches!(
+            event,
+            Ok(ChatEvent::Delta {
+                content: Some(text),
+                ..
+            }) if text.contains("<|im_end|>")
+        )));
+    }
+
+    #[test]
+    fn glm_tool_calls_drop_post_call_special_tokens() {
+        let events = futures::executor::block_on(
+            processor(Some("glm45"), None, 1)
+                .process_stream(stream::iter(vec![
+                    chunk(
+                        0,
+                        "<tool_call>get_weather\n<arg_key>city</arg_key>\n<arg_value>Paris</arg_value>\n</tool_call>",
+                        false,
+                    ),
+                    chunk(0, "Follow-up text", false),
+                    chunk(0, "<|user|>", true),
+                ]))
+                .collect::<Vec<_>>(),
+        );
+
+        let content = events
+            .iter()
+            .filter_map(|event| match event {
+                Ok(ChatEvent::Delta {
+                    content: Some(text),
+                    ..
+                }) => Some(text.as_str()),
+                _ => None,
+            })
+            .collect::<String>();
+        assert_eq!(content, "Follow-up text");
+        assert!(events.iter().any(|event| matches!(
+            event,
+            Ok(ChatEvent::Delta {
+                tool_calls: Some(calls),
+                ..
+            }) if calls.iter().any(|call| call.name.as_deref() == Some("get_weather"))
+        )));
+    }
+}

rust/sglang-renderer/src/preprocessing/chat.rs

@@ -0,0 +1,905 @@
+//! Transport-neutral chat preprocessing over a canonical OpenAI-compatible
+//! message vocabulary.
+
+use std::collections::HashMap;
+
+use dynamo_parsers::parsers::get_tool_parser_map;
+use dynamo_parsers::{
+    StructuralTagBuilder, StructuralTagSchemaMode, ToolCallFormatBuildContext,
+    ToolChoice as DynamoToolChoice, ToolDefinition, TriggeredTagsConfig,
+};
+use dynamo_protocols::types::{
+    ChatCompletionRequestAssistantMessageContent, ChatCompletionRequestMessage, ChatCompletionTool,
+    ChatCompletionToolChoiceOption, ResponseFormat,
+};
+use dynamo_renderer::{
+    OAIChatLikeRequest, RenderedPrompt, RenderedSegment, may_be_fix_tool_schema,
+};
+use minijinja::Value;
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
+
+use crate::ChatResponseProcessor;
+use crate::{
+    ChatFormatter, GenerateRequestMetadata, GenerationOptions, OneOrMany, RendererConfig,
+    RendererError, SamplingParams, TextRequest,
+};
+
+use super::{GenerateRequestIdentity, TextRequestGroup};
+
+/// SGLang reasoning effort, including Inkling's fine-grained numeric form.
+#[derive(Debug, Clone, PartialEq)]
+pub enum ReasoningEffort {
+    None,
+    Minimal,
+    Low,
+    Medium,
+    High,
+    XHigh,
+    Max,
+    Numeric(f64),
+}
+
+impl ReasoningEffort {
+    pub(crate) const fn disables_thinking(&self) -> bool {
+        matches!(self, Self::None)
+    }
+
+    const fn name(&self) -> Option<&'static str> {
+        match self {
+            Self::None => Some("none"),
+            Self::Minimal => Some("minimal"),
+            Self::Low => Some("low"),
+            Self::Medium => Some("medium"),
+            Self::High => Some("high"),
+            Self::XHigh => Some("xhigh"),
+            Self::Max => Some("max"),
+            Self::Numeric(_) => None,
+        }
+    }
+}
+
+impl Serialize for ReasoningEffort {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        match self {
+            Self::Numeric(value) => serializer.serialize_f64(*value),
+            _ => serializer.serialize_str(self.name().expect("named reasoning effort")),
+        }
+    }
+}
+
+impl<'de> Deserialize<'de> for ReasoningEffort {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let value = serde_json::Value::deserialize(deserializer)?;
+        match value {
+            serde_json::Value::String(value) => {
+                let effort = match value.as_str() {
+                    "none" => Some(Self::None),
+                    "minimal" => Some(Self::Minimal),
+                    "low" => Some(Self::Low),
+                    "medium" => Some(Self::Medium),
+                    "high" => Some(Self::High),
+                    "xhigh" => Some(Self::XHigh),
+                    "max" => Some(Self::Max),
+                    _ => None,
+                };
+                if let Some(effort) = effort {
+                    return Ok(effort);
+                }
+                let numeric = value.parse::<f64>().map_err(|_| {
+                    serde::de::Error::custom(format!("invalid reasoning effort: {value:?}"))
+                })?;
+                numeric_reasoning_effort(numeric).map_err(serde::de::Error::custom)
+            }
+            serde_json::Value::Number(value) => {
+                let numeric = value.as_f64().ok_or_else(|| {
+                    serde::de::Error::custom("reasoning_effort must be a finite number")
+                })?;
+                numeric_reasoning_effort(numeric).map_err(serde::de::Error::custom)
+            }
+            serde_json::Value::Bool(_) => Err(serde::de::Error::custom(
+                "reasoning_effort must not be a boolean",
+            )),
+            _ => Err(serde::de::Error::custom(
+                "reasoning_effort must be a string or number",
+            )),
+        }
+    }
+}
+
+fn numeric_reasoning_effort(value: f64) -> Result<ReasoningEffort, String> {
+    if !value.is_finite() || !(0.0..=0.99).contains(&value) {
+        return Err(format!(
+            "reasoning_effort must be a finite number in [0.0, 0.99], got {value}"
+        ));
+    }
+    Ok(ReasoningEffort::Numeric(value))
+}
+
+/// Renderer-owned normalized chat state.
+///
+/// Message and tool values remain Dynamo OpenAI protocol types until
+/// [`ChatPreprocessor`] applies the model chat template and lowers the request
+/// to the same [`TextRequest`] consumed by text completions.
+#[derive(Debug, Clone)]
+pub struct ChatRequest {
+    pub rid: String,
+    pub model: String,
+    pub messages: Vec<ChatCompletionRequestMessage>,
+    pub tools: Option<Vec<ChatCompletionTool>>,
+    pub tool_choice: Option<ChatCompletionToolChoiceOption>,
+    pub response_format: Option<ResponseFormat>,
+    pub reasoning_effort: Option<ReasoningEffort>,
+    pub continue_final_message: bool,
+    pub chat_template_args: Option<HashMap<String, serde_json::Value>>,
+    pub sampling_params: SamplingParams,
+    pub choice_count: usize,
+    pub stream: bool,
+    pub return_logprob: bool,
+    pub top_logprobs_num: i64,
+    pub parallel_tool_calls: bool,
+    pub metadata: GenerateRequestMetadata,
+}
+
+impl OAIChatLikeRequest for ChatRequest {
+    fn model(&self) -> String {
+        self.model.clone()
+    }
+
+    fn messages(&self) -> Value {
+        Value::from_serialize(
+            serde_json::to_value(&self.messages).expect("chat messages serialize"),
+        )
+    }
+
+    fn typed_messages(&self) -> Option<&[ChatCompletionRequestMessage]> {
+        Some(&self.messages)
+    }
+
+    fn tools(&self) -> Option<Value> {
+        self.tools.as_ref().and_then(|tools| {
+            may_be_fix_tool_schema(serde_json::to_value(tools).expect("chat tools serialize"))
+        })
+    }
+
+    fn tool_choice(&self) -> Option<Value> {
+        self.tool_choice.as_ref().map(Value::from_serialize)
+    }
+
+    fn response_format(&self) -> Option<Value> {
+        self.response_format.as_ref().map(Value::from_serialize)
+    }
+
+    fn reasoning_effort(&self) -> Option<Value> {
+        self.reasoning_effort.as_ref().map(Value::from_serialize)
+    }
+
+    fn should_add_generation_prompt(&self) -> bool {
+        !self.continue_final_message
+    }
+
+    fn chat_template_args(&self) -> Option<&HashMap<String, serde_json::Value>> {
+        self.chat_template_args.as_ref()
+    }
+}
+
+/// Chat-to-text result plus the state needed to interpret generated output.
+pub(crate) struct LoweredChat {
+    pub text_requests: Vec<TextRequestGroup>,
+    pub response_processor: ChatResponseProcessor,
+}
+
+struct RenderPreparation {
+    require_reasoning: bool,
+    reasoning_state: Option<bool>,
+    tools_enabled: bool,
+}
+
+/// Applies structured chat semantics before the shared text generation path.
+pub struct ChatPreprocessor {
+    formatter: Option<ChatFormatter>,
+    formatter_error: Option<String>,
+    tool_call_parser: Option<String>,
+    reasoning_parser: Option<String>,
+    default_chat_template_kwargs: HashMap<String, serde_json::Value>,
+}
+
+impl ChatPreprocessor {
+    pub(crate) fn new(config: &RendererConfig, formatter: Option<ChatFormatter>) -> Self {
+        Self {
+            formatter,
+            formatter_error: None,
+            tool_call_parser: config.tool_call_parser.clone(),
+            reasoning_parser: config.reasoning_parser.clone(),
+            default_chat_template_kwargs: config.default_chat_template_kwargs.clone(),
+        }
+    }
+
+    pub(crate) fn with_formatter_error(mut self, error: Option<String>) -> Self {
+        self.formatter_error = error;
+        self
+    }
+
+    pub fn preprocess(&self, mut request: ChatRequest) -> Result<LoweredChat, RendererError> {
+        let preparation = self.prepare_for_render(&mut request)?;
+        merge_template_stops(&mut request.sampling_params, self.formatter.as_ref());
+
+        let tool_choice = dynamo_tool_choice(&request.tool_choice);
+        let tools = chat_tool_definitions(&request);
+        let parser =
+            resolve_chat_parser(self.tool_call_parser.as_deref(), preparation.tools_enabled)?;
+        if parser.is_some() {
+            request.sampling_params.skip_special_tokens = false;
+        }
+        apply_tool_constraint(
+            &mut request.sampling_params,
+            parser.as_deref(),
+            &tool_choice,
+            &tools,
+            Some(request.parallel_tool_calls),
+        )?;
+        let prompt = self.render(&request)?;
+        let uses_tool_call_structural_tag = request.sampling_params.structural_tag.is_some();
+
+        let options = GenerationOptions {
+            sampling_params: request.sampling_params.clone(),
+            require_reasoning: preparation.require_reasoning,
+            stream: request.stream,
+            return_logprob: request.return_logprob,
+            logprob_start_len: -1,
+            top_logprobs_num: request.top_logprobs_num,
+            return_text_in_logprobs: request.return_logprob.then_some(true),
+            ..Default::default()
+        };
+        let mut choices = Vec::with_capacity(request.choice_count);
+        for index in 0..request.choice_count {
+            choices.push(GenerateRequestIdentity {
+                rid: format!("{}-{index}", request.rid),
+                metadata: request.metadata.clone(),
+            });
+        }
+        let text_requests = vec![TextRequestGroup {
+            prompt,
+            add_special_tokens: false,
+            options,
+            requests: choices,
+        }];
+
+        let response_processor = ChatResponseProcessor::new(
+            parser,
+            self.reasoning_parser.clone(),
+            (!tools.is_empty()).then_some(tools),
+            request.tool_choice,
+            uses_tool_call_structural_tag,
+            request.parallel_tool_calls,
+            request.choice_count,
+        )
+        .with_reasoning_state(preparation.reasoning_state);
+        Ok(LoweredChat {
+            text_requests,
+            response_processor,
+        })
+    }
+
+    /// Render chat for tokenization without creating generation/output state.
+    pub fn lower_to_text(&self, mut request: ChatRequest) -> Result<TextRequest, RendererError> {
+        let preparation = self.prepare_for_render(&mut request)?;
+        let prompt = self.render(&request)?;
+        Ok(TextRequest::rendered(
+            request.rid,
+            prompt,
+            false,
+            GenerationOptions {
+                sampling_params: request.sampling_params,
+                require_reasoning: preparation.require_reasoning,
+                ..Default::default()
+            },
+        )
+        .with_metadata(request.metadata))
+    }
+
+    fn prepare_for_render(
+        &self,
+        request: &mut ChatRequest,
+    ) -> Result<RenderPreparation, RendererError> {
+        validate_chat(request)?;
+        self.normalize_template_args(request);
+        let tool_choice = dynamo_tool_choice(&request.tool_choice);
+        let tools_enabled = request
+            .tools
+            .as_ref()
+            .is_some_and(|tools| !tools.is_empty())
+            && tool_choice != DynamoToolChoice::None;
+        let named_tool_choice = matches!(tool_choice, DynamoToolChoice::Named(_));
+        let thinking = self.formatter.as_ref().and_then(|formatter| {
+            formatter.resolve_thinking(
+                &mut request.chat_template_args,
+                tools_enabled,
+                named_tool_choice,
+            )
+        });
+        Ok(RenderPreparation {
+            require_reasoning: self.reasoning_parser.is_some() && thinking == Some(true),
+            reasoning_state: thinking,
+            tools_enabled,
+        })
+    }
+
+    fn normalize_template_args(&self, request: &mut ChatRequest) {
+        let request_args = request.chat_template_args.take().unwrap_or_default();
+        let mut args = self.default_chat_template_kwargs.clone();
+        if let Some(reasoning_effort) = request.reasoning_effort.as_ref() {
+            args.insert(
+                "reasoning_effort".into(),
+                serde_json::to_value(reasoning_effort).expect("reasoning effort must serialize"),
+            );
+            let thinking = !reasoning_effort.disables_thinking();
+            let has_explicit_toggle = request_args.contains_key("thinking")
+                || request_args.contains_key("enable_thinking");
+            if !has_explicit_toggle {
+                args.insert("thinking".into(), thinking.into());
+                args.insert("enable_thinking".into(), thinking.into());
+            }
+        }
+        args.extend(request_args);
+        request.chat_template_args = (!args.is_empty()).then_some(args);
+    }
+
+    fn render(&self, request: &ChatRequest) -> Result<RenderedPrompt, RendererError> {
+        let formatter = self.formatter.as_ref().ok_or_else(|| {
+            RendererError::from(
+                self.formatter_error
+                    .clone()
+                    .unwrap_or_else(|| "this model has no usable chat template".to_owned()),
+            )
+        })?;
+        let mut request = request.clone();
+        let final_message = prepare_continuation(&mut request);
+        let template_args = request.chat_template_args.get_or_insert_with(HashMap::new);
+        template_args.insert(
+            "add_generation_prompt".into(),
+            (!request.continue_final_message).into(),
+        );
+        template_args.insert(
+            "continue_final_message".into(),
+            request.continue_final_message.into(),
+        );
+        let prompt = formatter
+            .render_prompt(&request)
+            .map_err(|error| format!("chat template render failed: {error}"))?;
+        match final_message {
+            Some(final_message) => truncate_continuation(prompt, &final_message),
+            None => Ok(prompt),
+        }
+    }
+}
+
+const CONTINUE_FINAL_MESSAGE_TAG: &str = "CONTINUE_FINAL_MESSAGE_TAG ";
+
+fn prepare_continuation(request: &mut ChatRequest) -> Option<String> {
+    if !request.continue_final_message {
+        return None;
+    }
+    let Some(ChatCompletionRequestMessage::Assistant(message)) = request.messages.last_mut() else {
+        request.continue_final_message = false;
+        return None;
+    };
+    let Some(ChatCompletionRequestAssistantMessageContent::Text(text)) = message.content.as_mut()
+    else {
+        request.continue_final_message = false;
+        return None;
+    };
+    let original = text.clone();
+    text.push_str(CONTINUE_FINAL_MESSAGE_TAG);
+    Some(original)
+}
+
+fn truncate_continuation(
+    prompt: RenderedPrompt,
+    final_message: &str,
+) -> Result<RenderedPrompt, RendererError> {
+    let text = prompt.as_str();
+    let tag_location = text
+        .rfind(CONTINUE_FINAL_MESSAGE_TAG.trim_end())
+        .filter(|_| text.contains(final_message.trim()))
+        .ok_or_else(|| {
+            RendererError::from(
+                "continue_final_message is set but the final message does not appear in the rendered prompt",
+            )
+        })?;
+    let truncate_at = if text[tag_location..].starts_with(CONTINUE_FINAL_MESSAGE_TAG) {
+        tag_location
+    } else {
+        text[..tag_location].trim_end().len()
+    };
+    Ok(truncate_rendered_prompt(&prompt, truncate_at))
+}
+
+fn truncate_rendered_prompt(prompt: &RenderedPrompt, truncate_at: usize) -> RenderedPrompt {
+    let Some(segments) = prompt.segments() else {
+        return RenderedPrompt::text(prompt.as_str()[..truncate_at].to_owned());
+    };
+    let mut remaining = truncate_at;
+    let mut truncated = Vec::new();
+    for segment in segments {
+        if remaining == 0 {
+            break;
+        }
+        let take = remaining.min(segment.text.len());
+        if take != 0 {
+            truncated.push(RenderedSegment::new(
+                segment.text[..take].to_owned(),
+                segment.allow_special,
+            ));
+        }
+        remaining -= take;
+    }
+    RenderedPrompt::segmented(truncated)
+}
+
+fn validate_chat(request: &ChatRequest) -> Result<(), RendererError> {
+    if request.messages.is_empty() {
+        return Err("messages cannot be empty".into());
+    }
+    if request.choice_count == 0 {
+        return Err("choice_count must be at least 1".into());
+    }
+    if serde_json::to_value(&request.messages).is_ok_and(|messages| contains_media(&messages)) {
+        return Err("image, audio, video, and file message content is not supported".into());
+    }
+    Ok(())
+}
+
+fn contains_media(value: &serde_json::Value) -> bool {
+    match value {
+        serde_json::Value::Array(values) => values.iter().any(contains_media),
+        serde_json::Value::Object(object) => {
+            object.keys().any(|key| {
+                matches!(
+                    key.as_str(),
+                    "image_url" | "video_url" | "input_audio" | "audio_url" | "file"
+                )
+            }) || object.values().any(contains_media)
+        }
+        _ => false,
+    }
+}
+
+fn merge_template_stops(sampling: &mut SamplingParams, formatter: Option<&ChatFormatter>) {
+    let Some(template_stops) = formatter.and_then(ChatFormatter::stop_strs) else {
+        return;
+    };
+    let mut stops = match template_stops {
+        OneOrMany::One(stop) => vec![stop],
+        OneOrMany::Many(stops) => stops,
+    };
+    if let Some(request_stops) = sampling.stop.take() {
+        match request_stops {
+            OneOrMany::One(stop) => stops.push(stop),
+            OneOrMany::Many(request_stops) => stops.extend(request_stops),
+        }
+    }
+    sampling.stop = Some(OneOrMany::Many(stops));
+}
+
+fn resolve_chat_parser(
+    configured_parser: Option<&str>,
+    tools_enabled: bool,
+) -> Result<Option<String>, RendererError> {
+    if tools_enabled && configured_parser.is_none() {
+        return Err("tool calls require --tool-call-parser".into());
+    }
+    Ok(tools_enabled.then(|| configured_parser.expect("checked").to_owned()))
+}
+
+fn chat_tool_definitions(request: &ChatRequest) -> Vec<ToolDefinition> {
+    request
+        .tools
+        .iter()
+        .flatten()
+        .map(|tool| ToolDefinition {
+            name: tool.function.name.clone(),
+            parameters: tool.function.parameters.clone(),
+            strict: tool.function.strict,
+        })
+        .collect()
+}
+
+pub(crate) fn dynamo_parser_name(parser: &str) -> &str {
+    match parser {
+        "llama3" => "llama3_json",
+        "qwen" => "qwen25",
+        "glm" | "glm45" => "glm47",
+        other => other,
+    }
+}
+
+fn dynamo_tool_choice(choice: &Option<ChatCompletionToolChoiceOption>) -> DynamoToolChoice {
+    match choice {
+        Some(ChatCompletionToolChoiceOption::None) => DynamoToolChoice::None,
+        Some(ChatCompletionToolChoiceOption::Required) => DynamoToolChoice::Required,
+        Some(ChatCompletionToolChoiceOption::Named(choice)) => {
+            DynamoToolChoice::Named(choice.function.name.clone())
+        }
+        Some(ChatCompletionToolChoiceOption::Auto) | None => DynamoToolChoice::Auto,
+    }
+}
+
+fn apply_tool_constraint(
+    sampling: &mut SamplingParams,
+    parser: Option<&str>,
+    tool_choice: &DynamoToolChoice,
+    tools: &[ToolDefinition],
+    parallel_tool_calls: Option<bool>,
+) -> Result<(), String> {
+    if *tool_choice == DynamoToolChoice::None {
+        return Ok(());
+    }
+    if *tool_choice == DynamoToolChoice::Required && tools.is_empty() {
+        return Err("tool_choice is \"required\" but tools is empty".into());
+    }
+    if let DynamoToolChoice::Named(name) = tool_choice
+        && !tools.iter().any(|tool| &tool.name == name)
+    {
+        return Err(format!(
+            "tool named \"{name}\" in tool_choice is not present in tools"
+        ));
+    }
+
+    let Some(parser) = parser else {
+        return Ok(());
+    };
+    let parser = dynamo_parser_name(parser);
+    let config = get_tool_parser_map()
+        .get(parser)
+        .ok_or_else(|| format!("tool-call parser `{parser}` is not supported by Dynamo"))?;
+    let builder = config.structural_tag_builder.clone().or_else(|| {
+        (parser == "llama3_json"
+            && *tool_choice == DynamoToolChoice::Auto
+            && tools.iter().any(|tool| tool.strict.unwrap_or(false)))
+        .then(|| {
+            StructuralTagBuilder::TriggeredTags(TriggeredTagsConfig {
+                begin_template: r#"<|python_tag|>{"name":"{name}", "arguments":"#.to_string(),
+                end_template: "}".to_string(),
+                triggers: vec!["<|python_tag|>".to_string()],
+                content_style: Default::default(),
+                tool_call_ban_tokens: Vec::new(),
+                reasoning_end: None,
+            })
+        })
+    });
+    if let Some(builder) = builder
+        && let Some(tag) = builder
+            .build_tool_call_format(&ToolCallFormatBuildContext {
+                tool_choice,
+                tools,
+                parallel_tool_calls,
+                schema_mode: StructuralTagSchemaMode::Auto,
+                starts_in_reasoning: false,
+            })
+            .map_err(|error| error.to_string())?
+    {
+        sampling.structural_tag = Some(tag.to_string());
+        return Ok(());
+    }
+
+    if matches!(
+        tool_choice,
+        DynamoToolChoice::Required | DynamoToolChoice::Named(_)
+    ) {
+        let selected = match tool_choice {
+            DynamoToolChoice::Named(name) => tools
+                .iter()
+                .filter(|tool| tool.name == *name)
+                .collect::<Vec<_>>(),
+            _ => tools.iter().collect(),
+        };
+        let schemas = selected
+            .into_iter()
+            .map(|tool| {
+                serde_json::json!({
+                    "properties": {
+                        "name": {"type": "string", "enum": [tool.name]},
+                        "parameters": tool.parameters.clone().unwrap_or_else(|| {
+                            serde_json::json!({"type": "object", "properties": {}})
+                        }),
+                    },
+                    "required": ["name", "parameters"],
+                })
+            })
+            .collect::<Vec<_>>();
+        let items = if schemas.len() == 1 {
+            schemas.into_iter().next().expect("one schema")
+        } else {
+            serde_json::json!({"type": "object", "anyOf": schemas})
+        };
+        let mut schema = serde_json::json!({
+            "type": "array",
+            "minItems": 1,
+            "items": items,
+        });
+        if parallel_tool_calls == Some(false) {
+            schema["maxItems"] = serde_json::json!(1);
+        }
+        sampling.json_schema = Some(schema.to_string());
+    }
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::{RendererLimits, SamplingDefaults};
+    use dynamo_protocols::types::{
+        ChatCompletionNamedToolChoice, ChatCompletionToolType, FunctionName,
+    };
+
+    fn tool(name: &str, strict: bool) -> ToolDefinition {
+        ToolDefinition {
+            name: name.into(),
+            parameters: Some(serde_json::json!({
+                "type": "object",
+                "properties": {"city": {"type": "string"}},
+                "required": ["city"]
+            })),
+            strict: Some(strict),
+        }
+    }
+
+    fn chat_request(tool_choice: Option<ChatCompletionToolChoiceOption>) -> ChatRequest {
+        ChatRequest {
+            rid: "chatcmpl-test".into(),
+            model: "model".into(),
+            messages: serde_json::from_value(serde_json::json!([
+                {"role": "user", "content": "hello"}
+            ]))
+            .unwrap(),
+            tools: Some(
+                serde_json::from_value(serde_json::json!([{
+                    "type": "function",
+                    "function": {
+                        "name": "get_weather",
+                        "parameters": {"type": "object"}
+                    }
+                }]))
+                .unwrap(),
+            ),
+            tool_choice,
+            response_format: None,
+            reasoning_effort: None,
+            continue_final_message: false,
+            chat_template_args: None,
+            sampling_params: SamplingParams::default(),
+            choice_count: 1,
+            stream: false,
+            return_logprob: false,
+            top_logprobs_num: 0,
+            parallel_tool_calls: true,
+            metadata: GenerateRequestMetadata::default(),
+        }
+    }
+
+    fn chat_preprocessor() -> ChatPreprocessor {
+        chat_preprocessor_with(
+            Some("llama3"),
+            None,
+            crate::preprocessing::template::load_chat_formatter(None, None, Some("chatml"))
+                .unwrap(),
+        )
+    }
+
+    fn chat_preprocessor_with(
+        tool_call_parser: Option<&str>,
+        reasoning_parser: Option<&str>,
+        formatter: ChatFormatter,
+    ) -> ChatPreprocessor {
+        let config = RendererConfig {
+            served_model_name: "model".into(),
+            tokenizer_path: ".".into(),
+            revision: None,
+            model_path: String::new(),
+            chat_template: Some("chatml".into()),
+            tool_call_parser: tool_call_parser.map(str::to_owned),
+            reasoning_parser: reasoning_parser.map(str::to_owned),
+            default_chat_template_kwargs: Default::default(),
+            stream_response_default_include_usage: false,
+            default_sampling_params: SamplingDefaults::default(),
+            limits: RendererLimits {
+                vocab_size: 128,
+                context_len: 128,
+                num_reserved_tokens: 0,
+                allow_auto_truncate: false,
+                enable_return_hidden_states: false,
+            },
+        };
+        ChatPreprocessor::new(&config, Some(formatter))
+    }
+
+    #[test]
+    fn wire_tool_choices_lower_to_internal_choices() {
+        let named = Some(ChatCompletionToolChoiceOption::Named(
+            ChatCompletionNamedToolChoice {
+                r#type: ChatCompletionToolType::Function,
+                function: FunctionName {
+                    name: "get_weather".into(),
+                },
+            },
+        ));
+
+        assert!(matches!(dynamo_tool_choice(&None), DynamoToolChoice::Auto));
+        assert!(matches!(
+            dynamo_tool_choice(&Some(ChatCompletionToolChoiceOption::Required)),
+            DynamoToolChoice::Required
+        ));
+        assert!(matches!(
+            dynamo_tool_choice(&named),
+            DynamoToolChoice::Named(name) if name == "get_weather"
+        ));
+    }
+
+    #[test]
+    fn required_choice_builds_a_single_call_constraint() {
+        let mut sampling = SamplingParams::default();
+        apply_tool_constraint(
+            &mut sampling,
+            Some("llama3"),
+            &DynamoToolChoice::Required,
+            &[tool("get_weather", false), tool("get_time", false)],
+            Some(false),
+        )
+        .unwrap();
+
+        let schema: serde_json::Value =
+            serde_json::from_str(sampling.json_schema.as_deref().unwrap()).unwrap();
+        assert_eq!(schema["minItems"], 1);
+        assert_eq!(schema["maxItems"], 1);
+    }
+
+    #[test]
+    fn invalid_tool_choices_are_rejected_before_generation() {
+        let mut sampling = SamplingParams::default();
+        assert!(
+            apply_tool_constraint(&mut sampling, None, &DynamoToolChoice::Required, &[], None,)
+                .unwrap_err()
+                .contains("required")
+        );
+        assert!(
+            apply_tool_constraint(
+                &mut sampling,
+                None,
+                &DynamoToolChoice::Named("missing".into()),
+                &[tool("get_weather", false)],
+                None,
+            )
+            .unwrap_err()
+            .contains("missing")
+        );
+    }
+
+    #[test]
+    fn tool_parsing_preserves_special_tokens_for_output_processing() {
+        let mut request = chat_request(None);
+        request.sampling_params.skip_special_tokens = true;
+
+        let chat = chat_preprocessor().preprocess(request).unwrap();
+
+        assert!(
+            !chat.text_requests[0]
+                .options
+                .sampling_params
+                .skip_special_tokens
+        );
+    }
+
+    #[test]
+    fn tool_choice_none_keeps_the_requested_special_token_behavior() {
+        let mut request = chat_request(Some(ChatCompletionToolChoiceOption::None));
+        request.sampling_params.skip_special_tokens = true;
+
+        let chat = chat_preprocessor().preprocess(request).unwrap();
+
+        assert!(
+            chat.text_requests[0]
+                .options
+                .sampling_params
+                .skip_special_tokens
+        );
+    }
+
+    #[test]
+    fn qwen_required_tools_forward_effective_template_thinking() {
+        let formatter = crate::preprocessing::template::test_hugging_face_formatter(
+            "{% if enable_thinking is not defined %}{% set enable_thinking = true %}{% endif %}{{ enable_thinking }}",
+        );
+        let preprocessor = chat_preprocessor_with(Some("qwen"), Some("qwen3"), formatter);
+
+        let enabled = preprocessor
+            .preprocess(chat_request(Some(ChatCompletionToolChoiceOption::Required)))
+            .unwrap();
+        assert!(enabled.text_requests[0].options.require_reasoning);
+
+        let mut disabled_request = chat_request(Some(ChatCompletionToolChoiceOption::Required));
+        disabled_request.reasoning_effort = Some(ReasoningEffort::Max);
+        disabled_request.chat_template_args = Some(HashMap::from([(
+            "enable_thinking".into(),
+            serde_json::Value::Bool(false),
+        )]));
+        let disabled = preprocessor.preprocess(disabled_request).unwrap();
+        assert!(!disabled.text_requests[0].options.require_reasoning);
+    }
+
+    #[test]
+    fn thinking_policy_uses_the_effective_tool_template() {
+        let formatter = crate::preprocessing::template::test_hugging_face_formatter_from_config(
+            serde_json::json!({
+                "chat_template": [
+                    {"default": "{{ enable_thinking | default(false) }}"},
+                    {"tool_use": "{{ enable_thinking | default(true) }}"}
+                ]
+            }),
+        );
+        let preprocessor = chat_preprocessor_with(Some("qwen"), Some("qwen3"), formatter);
+
+        let mut no_tools = chat_request(None);
+        no_tools.tools = None;
+        assert!(
+            !preprocessor.preprocess(no_tools).unwrap().text_requests[0]
+                .options
+                .require_reasoning
+        );
+
+        let mut empty_tools = chat_request(None);
+        empty_tools.tools = Some(Vec::new());
+        assert!(
+            !preprocessor.preprocess(empty_tools).unwrap().text_requests[0]
+                .options
+                .require_reasoning
+        );
+
+        assert!(
+            !preprocessor
+                .preprocess(chat_request(Some(ChatCompletionToolChoiceOption::None)))
+                .unwrap()
+                .text_requests[0]
+                .options
+                .require_reasoning
+        );
+        assert!(
+            preprocessor
+                .preprocess(chat_request(Some(ChatCompletionToolChoiceOption::Required)))
+                .unwrap()
+                .text_requests[0]
+                .options
+                .require_reasoning
+        );
+    }
+
+    #[test]
+    fn always_on_channel_template_requires_reasoning() {
+        let formatter = crate::preprocessing::template::test_hugging_face_formatter(
+            "<|start|>assistant<|channel|>analysis<|message|>",
+        );
+        let preprocessor = chat_preprocessor_with(None, Some("gpt-oss"), formatter);
+        let mut request = chat_request(None);
+        request.tools = None;
+        request.response_format = Some(
+            serde_json::from_value(serde_json::json!({
+                "type": "json_schema",
+                "json_schema": {
+                    "name": "answer",
+                    "schema": {"type": "object"}
+                }
+            }))
+            .unwrap(),
+        );
+
+        let lowered = preprocessor.preprocess(request).unwrap();
+
+        assert!(lowered.text_requests[0].options.require_reasoning);
+    }
+}

rust/sglang-renderer/src/preprocessing/mod.rs

@@ -0,0 +1,28 @@
+//! Request processing from protocol-neutral inputs to token-only generation requests.
+
+mod chat;
+mod regex;
+mod request;
+mod sampling;
+mod service;
+mod template;
+mod tokenizer;
+
+pub(crate) use chat::{ChatPreprocessor, LoweredChat, dynamo_parser_name};
+pub use chat::{ChatRequest, ReasoningEffort};
+pub use request::{
+    GenerateRequest, GenerateRequestMetadata, GenerateSamplingParams, GenerationOptions,
+    TextRequest, TokenIdsRequest,
+};
+pub(crate) use request::{GenerateRequestIdentity, TextRequestGroup};
+pub use sampling::SamplingParams;
+pub(crate) use sampling::SamplingParamsOverrides;
+pub use service::{PreparedChat, RendererService};
+pub(crate) use template::ChatFormatter;
+#[cfg(test)]
+pub(crate) fn load_test_chat_formatter(name: &str) -> ChatFormatter {
+    template::load_chat_formatter(None, None, Some(name)).unwrap()
+}
+pub use tokenizer::{DynamoTokenizer, TextTokenizer, load_tokenizer};
+#[cfg(feature = "http")]
+pub(crate) use tokenizer::{resolve_model_file, resolve_tokenizer_file};

rust/sglang-renderer/src/preprocessing/request.rs

@@ -0,0 +1,282 @@
+//! Internal and transport request representations.
+
+use std::collections::BTreeMap;
+
+use dynamo_renderer::RenderedPrompt;
+use serde::{Deserialize, Serialize};
+
+use crate::{SamplingParams, TokenIds};
+
+/// Request-scoped metadata that must survive protocol lowering and prompt
+/// tokenization before the request is submitted to SGLang `/generate`.
+#[derive(Debug, Clone, Default, PartialEq, Serialize, Deserialize)]
+pub struct GenerateRequestMetadata {
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub model: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub cache_salt: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub extra_key: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub priority: Option<i64>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub bootstrap_host: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub bootstrap_port: Option<i64>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub bootstrap_room: Option<i64>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub routed_dp_rank: Option<i64>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub disagg_prefill_dp_rank: Option<i64>,
+}
+
+#[derive(Debug, Clone, Default)]
+/// Generation options shared by text and token-ID inputs.
+pub struct GenerationOptions {
+    pub sampling_params: SamplingParams,
+    /// Delay structured-output constraints until the model finishes reasoning.
+    pub require_reasoning: bool,
+    pub stream: bool,
+    pub return_logprob: bool,
+    pub logprob_start_len: i64,
+    pub top_logprobs_num: i64,
+    pub token_ids_logprob: Option<TokenIds>,
+    pub return_hidden_states: bool,
+    pub return_text_in_logprobs: Option<bool>,
+}
+
+#[derive(Debug, Clone)]
+/// Internal text-only generation request before tokenization.
+///
+/// Protocol adapters lower textual completions into this type. Structured chat
+/// reaches it only after [`crate::ChatPreprocessor`] renders the messages.
+pub struct TextRequest {
+    pub rid: String,
+    pub prompt: RenderedPrompt,
+    pub add_special_tokens: bool,
+    pub options: GenerationOptions,
+    pub metadata: GenerateRequestMetadata,
+}
+
+/// One textual prompt shared by one or more generation choices.
+///
+/// OpenAI `n` fan-out changes request identity, not the prompt or generation
+/// options. Keeping those identities alongside one prompt lets preprocessing
+/// tokenize the prompt once before producing the individual engine requests.
+#[derive(Debug, Clone)]
+pub(crate) struct TextRequestGroup {
+    pub prompt: RenderedPrompt,
+    pub add_special_tokens: bool,
+    pub options: GenerationOptions,
+    pub requests: Vec<GenerateRequestIdentity>,
+}
+
+#[derive(Debug, Clone)]
+pub(crate) struct GenerateRequestIdentity {
+    pub rid: String,
+    pub metadata: GenerateRequestMetadata,
+}
+
+impl From<TextRequest> for TextRequestGroup {
+    fn from(request: TextRequest) -> Self {
+        Self {
+            prompt: request.prompt,
+            add_special_tokens: request.add_special_tokens,
+            options: request.options,
+            requests: vec![GenerateRequestIdentity {
+                rid: request.rid,
+                metadata: request.metadata,
+            }],
+        }
+    }
+}
+
+impl TextRequest {
+    pub fn text(
+        rid: impl Into<String>,
+        text: impl Into<String>,
+        add_special_tokens: bool,
+        options: GenerationOptions,
+    ) -> Self {
+        Self {
+            rid: rid.into(),
+            prompt: RenderedPrompt::text(text.into()),
+            add_special_tokens,
+            options,
+            metadata: GenerateRequestMetadata::default(),
+        }
+    }
+
+    pub fn rendered(
+        rid: impl Into<String>,
+        prompt: RenderedPrompt,
+        add_special_tokens: bool,
+        options: GenerationOptions,
+    ) -> Self {
+        Self {
+            rid: rid.into(),
+            prompt,
+            add_special_tokens,
+            options,
+            metadata: GenerateRequestMetadata::default(),
+        }
+    }
+
+    pub fn with_metadata(mut self, metadata: GenerateRequestMetadata) -> Self {
+        self.metadata = metadata;
+        self
+    }
+}
+
+#[derive(Debug, Clone)]
+/// A generation request whose prompt is already represented by token IDs.
+pub struct TokenIdsRequest {
+    pub rid: String,
+    pub input_ids: TokenIds,
+    pub options: GenerationOptions,
+    pub metadata: GenerateRequestMetadata,
+}
+
+impl TokenIdsRequest {
+    pub fn new(rid: impl Into<String>, input_ids: TokenIds, options: GenerationOptions) -> Self {
+        Self {
+            rid: rid.into(),
+            input_ids,
+            options,
+            metadata: GenerateRequestMetadata::default(),
+        }
+    }
+
+    pub fn with_metadata(mut self, metadata: GenerateRequestMetadata) -> Self {
+        self.metadata = metadata;
+        self
+    }
+}
+
+/// Token-only request sent to the model server's `/generate` endpoint.
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub struct GenerateRequest {
+    pub rid: String,
+    #[serde(flatten)]
+    pub metadata: GenerateRequestMetadata,
+    pub input_ids: TokenIds,
+    #[serde(default)]
+    pub require_reasoning: bool,
+    pub sampling_params: GenerateSamplingParams,
+    pub stream: bool,
+    pub return_logprob: bool,
+    pub logprob_start_len: i64,
+    pub top_logprobs_num: i64,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub token_ids_logprob: Option<TokenIds>,
+    pub return_hidden_states: bool,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub return_text_in_logprobs: Option<bool>,
+}
+
+impl From<TokenIdsRequest> for GenerateRequest {
+    fn from(request: TokenIdsRequest) -> Self {
+        let options = request.options;
+        Self {
+            rid: request.rid,
+            metadata: request.metadata,
+            input_ids: request.input_ids,
+            require_reasoning: options.require_reasoning,
+            sampling_params: options.sampling_params.into(),
+            stream: options.stream,
+            return_logprob: options.return_logprob,
+            logprob_start_len: options.logprob_start_len,
+            top_logprobs_num: options.top_logprobs_num,
+            token_ids_logprob: options.token_ids_logprob,
+            return_hidden_states: options.return_hidden_states,
+            return_text_in_logprobs: options.return_text_in_logprobs,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn require_reasoning_is_forwarded_as_a_boolean() {
+        let request = |require_reasoning| {
+            GenerateRequest::from(TokenIdsRequest::new(
+                "request",
+                vec![1, 2],
+                GenerationOptions {
+                    require_reasoning,
+                    ..Default::default()
+                },
+            ))
+        };
+
+        let enabled = serde_json::to_value(request(true)).unwrap();
+        assert_eq!(enabled["require_reasoning"], true);
+
+        let disabled = serde_json::to_value(request(false)).unwrap();
+        assert_eq!(disabled["require_reasoning"], false);
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub struct GenerateSamplingParams {
+    pub max_new_tokens: Option<i64>,
+    pub stop: Vec<String>,
+    pub stop_token_ids: Option<Vec<i64>>,
+    pub stop_regex: Vec<String>,
+    pub temperature: f64,
+    pub top_p: f64,
+    pub top_k: i64,
+    pub min_p: f64,
+    pub frequency_penalty: f64,
+    pub presence_penalty: f64,
+    pub repetition_penalty: f64,
+    pub min_new_tokens: i64,
+    pub n: i64,
+    pub json_schema: Option<String>,
+    pub regex: Option<String>,
+    pub ebnf: Option<String>,
+    pub structural_tag: Option<String>,
+    pub ignore_eos: bool,
+    pub skip_special_tokens: bool,
+    pub spaces_between_special_tokens: bool,
+    pub no_stop_trim: bool,
+    pub stream_interval: Option<i64>,
+    pub logit_bias: Option<BTreeMap<String, f64>>,
+    pub sampling_seed: Option<i64>,
+    pub custom_params: Option<serde_json::Value>,
+}
+
+impl From<SamplingParams> for GenerateSamplingParams {
+    fn from(params: SamplingParams) -> Self {
+        Self {
+            max_new_tokens: params.max_new_tokens,
+            stop: params.stop_strs,
+            stop_token_ids: params.stop_token_ids,
+            stop_regex: params.stop_regex_strs,
+            temperature: params.temperature,
+            top_p: params.top_p,
+            top_k: params.top_k,
+            min_p: params.min_p,
+            frequency_penalty: params.frequency_penalty,
+            presence_penalty: params.presence_penalty,
+            repetition_penalty: params.repetition_penalty,
+            min_new_tokens: params.min_new_tokens,
+            n: params.n,
+            json_schema: params.json_schema,
+            regex: params.regex,
+            ebnf: params.ebnf,
+            structural_tag: params.structural_tag,
+            ignore_eos: params.ignore_eos,
+            skip_special_tokens: params.skip_special_tokens,
+            spaces_between_special_tokens: params.spaces_between_special_tokens,
+            no_stop_trim: params.no_stop_trim,
+            stream_interval: params.stream_interval,
+            logit_bias: params.logit_bias,
+            sampling_seed: params.sampling_seed,
+            custom_params: params.custom_params,
+        }
+    }
+}

rust/sglang-renderer/src/preprocessing/template/deepseek_v4.rs

@@ -0,0 +1,117 @@
+//! Adapt SGLang's DeepSeek V4 effort profiles to Dynamo's native formatter.
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) enum DeepSeekV4Profile {
+    Preview,
+    Official,
+}
+
+pub(super) fn dynamo_reasoning_effort(
+    profile: DeepSeekV4Profile,
+    effort: Option<&str>,
+) -> &'static str {
+    match (profile, effort) {
+        (DeepSeekV4Profile::Preview, Some("max")) | (DeepSeekV4Profile::Official, Some("high")) => {
+            "high"
+        }
+        (DeepSeekV4Profile::Official, Some("max")) => "max",
+        // Dynamo's low effort preserves thinking without adding a prefix.
+        _ => "low",
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashMap;
+    use std::sync::Arc;
+
+    use dynamo_protocols::types::CreateChatCompletionRequest;
+    use dynamo_renderer::PromptFormatter;
+    use dynamo_renderer::deepseek::v4::DeepSeekV4Formatter;
+
+    use super::super::{ChatFormatter, TemplateArgsRequest};
+    use super::DeepSeekV4Profile;
+
+    #[test]
+    fn deepseek_v4_profiles_map_effort_without_coercing_unsupported_tiers() {
+        fn render(
+            profile: DeepSeekV4Profile,
+            effort: Option<&str>,
+            thinking: Option<bool>,
+            environment_effort: Option<&str>,
+        ) -> String {
+            let request: CreateChatCompletionRequest = serde_json::from_value(serde_json::json!({
+                "model": "test",
+                "messages": [
+                    {"role": "system", "content": "Be concise."},
+                    {"role": "user", "content": "Hello"}
+                ]
+            }))
+            .unwrap();
+            let mut args = HashMap::new();
+            if let Some(effort) = effort {
+                args.insert("reasoning_effort".into(), serde_json::json!(effort));
+            }
+            if let Some(thinking) = thinking {
+                args.insert("thinking".into(), serde_json::json!(thinking));
+            }
+            ChatFormatter::DeepSeekV4 {
+                formatter: PromptFormatter::OAI(Arc::new(DeepSeekV4Formatter::new_chat())),
+                profile,
+                environment_effort: environment_effort.map(str::to_owned),
+            }
+            .render(&TemplateArgsRequest {
+                request: &request,
+                args,
+            })
+            .unwrap()
+        }
+
+        let baseline = "<｜begin▁of▁sentence｜>Be concise.<｜User｜>Hello<｜Assistant｜><think>";
+        for (profile, high_prefix, max_prefix) in [
+            (DeepSeekV4Profile::Preview, None, "Absolute maximum"),
+            (
+                DeepSeekV4Profile::Official,
+                Some("Absolute maximum"),
+                "Beyond maximum",
+            ),
+        ] {
+            for (effort, prefix) in [
+                (None, None),
+                (Some("low"), None),
+                (Some("high"), high_prefix),
+                (Some("max"), Some(max_prefix)),
+                (Some("xhigh"), None),
+            ] {
+                let prompt = render(profile, effort, Some(true), None);
+                assert_eq!(
+                    prompt.matches("Reasoning Effort:").count(),
+                    usize::from(prefix.is_some()),
+                    "{profile:?}, {effort:?}: {prompt}"
+                );
+                if let Some(prefix) = prefix {
+                    assert!(prompt.starts_with(&format!(
+                        "<｜begin▁of▁sentence｜>Reasoning Effort: {prefix}"
+                    )));
+                    assert_eq!(
+                        prompt.split_once("\n\n").unwrap().1,
+                        baseline.strip_prefix("<｜begin▁of▁sentence｜>").unwrap()
+                    );
+                } else {
+                    assert_eq!(prompt, baseline);
+                }
+            }
+            let disabled = baseline.replace("<think>", "</think>");
+            assert_eq!(render(profile, None, None, None), disabled);
+            assert_eq!(render(profile, Some("max"), Some(false), None), disabled);
+            assert_eq!(
+                render(profile, None, Some(true), Some("max")),
+                render(profile, Some("max"), Some(true), None)
+            );
+            assert_eq!(
+                render(profile, Some("low"), Some(true), Some("max")),
+                baseline
+            );
+        }
+    }
+}

rust/sglang-renderer/src/preprocessing/template/kimi_k25.rs

@@ -0,0 +1,725 @@
+//! Kimi K2.5 checkpoint-compatible tool declaration preprocessing.
+
+use std::collections::HashMap;
+use std::fmt::Write as _;
+
+use serde_json::{Map, Value};
+
+const INDENT: &str = "  ";
+const FIELD_DELIMITER: &str = ",\n";
+const MAX_RECURSION_DEPTH: usize = 32;
+
+pub(crate) fn deep_sort(value: &mut Value) {
+    match value {
+        Value::Object(object) => {
+            let mut entries: Vec<_> = std::mem::take(object).into_iter().collect();
+            for (_, value) in &mut entries {
+                deep_sort(value);
+            }
+            entries.sort_by(|left, right| left.0.cmp(&right.0));
+            *object = entries.into_iter().collect::<Map<_, _>>();
+        }
+        Value::Array(array) => {
+            for value in array {
+                deep_sort(value);
+            }
+        }
+        _ => {}
+    }
+}
+
+pub(crate) fn encode_tools_to_typescript(tools: &[Value]) -> Option<String> {
+    if tools.is_empty() {
+        return None;
+    }
+    let mut functions = Vec::new();
+    for tool in tools {
+        if tool.get("type").and_then(Value::as_str) != Some("function") {
+            continue;
+        }
+        let function = match tool.get("function") {
+            Some(function)
+                if function
+                    .as_object()
+                    .is_some_and(|object| !object.is_empty()) =>
+            {
+                function
+            }
+            _ => continue,
+        };
+        match encode_function(function) {
+            Some(function) => functions.push(function),
+            None => {
+                tracing::warn!(
+                    "Kimi K2.5 tool schema is unsupported by the TypeScript encoder; using the checkpoint JSON fallback"
+                );
+                return None;
+            }
+        }
+    }
+    if functions.is_empty() {
+        return None;
+    }
+    Some(format!(
+        "# Tools\n\n## functions\nnamespace functions {{\n{}\n}}\n",
+        functions.join("\n")
+    ))
+}
+
+fn encode_function(function: &Value) -> Option<String> {
+    let parameters = function
+        .get("parameters")
+        .cloned()
+        .unwrap_or_else(|| Value::Object(Map::new()));
+    let mut registry = SchemaRegistry::default();
+    let parsed = ObjectType::parse(&parameters, &mut registry);
+    let mut interfaces = Vec::new();
+
+    let root_name = if registry.has_self_ref {
+        let body = parsed
+            .properties
+            .iter()
+            .map(|parameter| parameter.to_typescript(INDENT, &registry))
+            .collect::<Vec<_>>()
+            .join(FIELD_DELIMITER);
+        let body = if body.is_empty() {
+            String::new()
+        } else {
+            format!("\n{body}\n")
+        };
+        interfaces.push(format!("interface parameters {{{body}}}"));
+        Some("parameters")
+    } else {
+        None
+    };
+
+    let definitions = registry
+        .order
+        .iter()
+        .filter_map(|name| {
+            registry
+                .definitions
+                .get(name)
+                .map(|schema| (name.clone(), schema.clone()))
+        })
+        .collect::<Vec<_>>();
+    for (name, schema) in definitions {
+        let object = parse_type(&schema, &mut registry);
+        let mut definition = String::new();
+        if let Some(description) = schema.get("description").and_then(Value::as_str)
+            && !description.is_empty()
+        {
+            definition.push_str(&format_description(description, ""));
+            definition.push('\n');
+        }
+        definition.push_str(&format!(
+            "interface {name} {}",
+            object.to_typescript("", &registry)
+        ));
+        interfaces.push(definition);
+    }
+
+    if registry.unsupported {
+        return None;
+    }
+    let name = function
+        .get("name")
+        .and_then(Value::as_str)
+        .unwrap_or("function");
+    let type_definition = match root_name {
+        Some(root_name) => format!("type {name} = (_: {root_name}) => any;"),
+        None => format!(
+            "type {name} = (_: {}) => any;",
+            parsed.to_typescript("", &registry)
+        ),
+    };
+    let description = function
+        .get("description")
+        .and_then(Value::as_str)
+        .filter(|description| !description.is_empty())
+        .map(|description| format_description(description, ""))
+        .unwrap_or_default();
+    Some(
+        [interfaces.join("\n"), description, type_definition]
+            .into_iter()
+            .filter(|part| !part.is_empty())
+            .collect::<Vec<_>>()
+            .join("\n"),
+    )
+}
+
+#[derive(Default)]
+struct SchemaRegistry {
+    definitions: HashMap<String, Value>,
+    order: Vec<String>,
+    has_self_ref: bool,
+    depth: usize,
+    unsupported: bool,
+}
+
+impl SchemaRegistry {
+    fn register_definitions(&mut self, definitions: &Value) {
+        if let Some(definitions) = definitions.as_object() {
+            for (name, schema) in definitions {
+                if !self.definitions.contains_key(name) {
+                    self.order.push(name.clone());
+                }
+                self.definitions.insert(name.clone(), schema.clone());
+            }
+        }
+    }
+
+    fn resolve_reference(&mut self, reference: &str) -> Option<Value> {
+        if reference == "#" {
+            self.has_self_ref = true;
+            return Some(serde_json::json!({"$self_ref": true}));
+        }
+        if let Some(name) = reference.strip_prefix("#/$defs/")
+            && let Some(definition) = self.definitions.get(name)
+        {
+            return Some(definition.clone());
+        }
+        self.unsupported = true;
+        None
+    }
+}
+
+enum ParameterType {
+    Scalar(ScalarType),
+    Object(ObjectType),
+    Array(ArrayType),
+    Enum(EnumType),
+    AnyOf(AnyOfType),
+    Union(UnionType),
+    Reference(ReferenceType),
+}
+
+impl ParameterType {
+    fn format_docstring(&self, indent: &str) -> String {
+        match self {
+            Self::Scalar(value) => value.base.format_docstring(indent),
+            Self::Object(value) => value.base.format_docstring(indent),
+            Self::Array(value) => value.base.format_docstring(indent),
+            Self::Enum(value) => value.base.format_docstring(indent),
+            Self::AnyOf(value) => value.base.format_docstring(indent),
+            Self::Union(value) => value.base.format_docstring(indent),
+            Self::Reference(value) => value.base.format_docstring(indent),
+        }
+    }
+
+    fn to_typescript(&self, indent: &str, registry: &SchemaRegistry) -> String {
+        match self {
+            Self::Scalar(value) => value.to_typescript(),
+            Self::Object(value) => value.to_typescript(indent, registry),
+            Self::Array(value) => value.to_typescript(indent, registry),
+            Self::Enum(value) => value.to_typescript(),
+            Self::AnyOf(value) => value.to_typescript(indent, registry),
+            Self::Union(value) => value.to_typescript(),
+            Self::Reference(value) => value.to_typescript(),
+        }
+    }
+}
+
+#[derive(Default)]
+struct BaseType {
+    description: String,
+    constraints: Vec<(String, Value)>,
+}
+
+impl BaseType {
+    fn new(schema: &Value, allowed_constraints: &[&str]) -> Self {
+        let description = schema
+            .get("description")
+            .and_then(Value::as_str)
+            .unwrap_or_default()
+            .to_owned();
+        let mut constraints = schema
+            .as_object()
+            .map(|object| {
+                object
+                    .iter()
+                    .filter(|(key, _)| allowed_constraints.contains(&key.as_str()))
+                    .map(|(key, value)| (key.clone(), value.clone()))
+                    .collect::<Vec<_>>()
+            })
+            .unwrap_or_default();
+        constraints.sort_by(|left, right| left.0.cmp(&right.0));
+        Self {
+            description,
+            constraints,
+        }
+    }
+
+    fn format_docstring(&self, indent: &str) -> String {
+        let mut output = String::new();
+        if !self.description.is_empty() {
+            output.push_str(&format_description(&self.description, indent));
+            output.push('\n');
+        }
+        if !self.constraints.is_empty() {
+            let constraints = self
+                .constraints
+                .iter()
+                .map(|(key, value)| format!("{key}: {}", json_inline(value)))
+                .collect::<Vec<_>>()
+                .join(", ");
+            output.push_str(&format!("{indent}// {constraints}\n"));
+        }
+        output
+    }
+}
+
+struct ScalarType {
+    base: BaseType,
+    kind: String,
+}
+
+impl ScalarType {
+    fn parse(kind: &str, schema: &Value) -> Self {
+        let constraints = match kind {
+            "string" => &["maxLength", "minLength", "pattern"][..],
+            "number" | "integer" => &["maximum", "minimum"][..],
+            _ => &[],
+        };
+        Self {
+            base: BaseType::new(schema, constraints),
+            kind: kind.to_owned(),
+        }
+    }
+
+    fn any() -> Self {
+        Self {
+            base: BaseType::default(),
+            kind: "any".into(),
+        }
+    }
+
+    fn to_typescript(&self) -> String {
+        if self.kind == "integer" {
+            "number".into()
+        } else {
+            self.kind.clone()
+        }
+    }
+}
+
+struct Parameter {
+    name: String,
+    kind: ParameterType,
+    optional: bool,
+    default: Option<Value>,
+}
+
+impl Parameter {
+    fn to_typescript(&self, indent: &str, registry: &SchemaRegistry) -> String {
+        let mut output = self.kind.format_docstring(indent);
+        if let Some(default) = &self.default {
+            let default = match default {
+                Value::Bool(true) => "True".into(),
+                Value::Bool(false) => "False".into(),
+                Value::Number(_) => default.to_string(),
+                _ => serde_json::to_string(default).unwrap_or_else(|_| "null".into()),
+            };
+            output.push_str(&format!("{indent}// Default: {default}\n"));
+        }
+        let optional = if self.optional { "?" } else { "" };
+        let _ = write!(
+            output,
+            "{indent}{}{optional}: {}",
+            self.name,
+            self.kind.to_typescript(indent, registry)
+        );
+        output
+    }
+}
+
+struct ObjectType {
+    base: BaseType,
+    properties: Vec<Parameter>,
+    additional_properties: AdditionalProperties,
+}
+
+enum AdditionalProperties {
+    None,
+    True,
+    False,
+    Schema(Box<ParameterType>),
+}
+
+impl ObjectType {
+    fn parse(schema: &Value, registry: &mut SchemaRegistry) -> Self {
+        if let Some(definitions) = schema.get("$defs") {
+            registry.register_definitions(definitions);
+        }
+        let additional_properties = match schema.get("additionalProperties") {
+            None => AdditionalProperties::None,
+            Some(Value::Bool(true)) => AdditionalProperties::True,
+            Some(Value::Bool(false)) => AdditionalProperties::False,
+            Some(schema) => AdditionalProperties::Schema(Box::new(parse_type(schema, registry))),
+        };
+        let required = schema
+            .get("required")
+            .and_then(Value::as_array)
+            .map(|values| values.iter().filter_map(Value::as_str).collect::<Vec<_>>())
+            .unwrap_or_default();
+        let properties = schema
+            .get("properties")
+            .and_then(Value::as_object)
+            .map(|properties| {
+                properties
+                    .iter()
+                    .map(|(name, schema)| Parameter {
+                        name: name.clone(),
+                        kind: parse_type(schema, registry),
+                        optional: !required.contains(&name.as_str()),
+                        default: schema
+                            .get("default")
+                            .filter(|value| !value.is_null())
+                            .cloned(),
+                    })
+                    .collect()
+            })
+            .unwrap_or_default();
+        Self {
+            base: BaseType::new(schema, &[]),
+            properties,
+            additional_properties,
+        }
+    }
+
+    fn to_typescript(&self, indent: &str, registry: &SchemaRegistry) -> String {
+        let mut required = self
+            .properties
+            .iter()
+            .filter(|parameter| !parameter.optional)
+            .collect::<Vec<_>>();
+        let mut optional = self
+            .properties
+            .iter()
+            .filter(|parameter| parameter.optional)
+            .collect::<Vec<_>>();
+        required.sort_by(|left, right| left.name.cmp(&right.name));
+        optional.sort_by(|left, right| left.name.cmp(&right.name));
+        let inner_indent = format!("{indent}{INDENT}");
+        let mut fields = required
+            .into_iter()
+            .chain(optional)
+            .map(|parameter| parameter.to_typescript(&inner_indent, registry))
+            .collect::<Vec<_>>();
+        match &self.additional_properties {
+            AdditionalProperties::None => {}
+            AdditionalProperties::True => fields.push(format!("{inner_indent}[k: string]: any")),
+            AdditionalProperties::False => {
+                fields.push(format!("{inner_indent}[k: string]: never"));
+            }
+            AdditionalProperties::Schema(schema) => fields.push(format!(
+                "{inner_indent}[k: string]: {}",
+                schema.to_typescript(&inner_indent, registry)
+            )),
+        }
+        if fields.is_empty() {
+            "{}".into()
+        } else {
+            format!("{{\n{}\n{indent}}}", fields.join(FIELD_DELIMITER))
+        }
+    }
+}
+
+struct ArrayType {
+    base: BaseType,
+    item: Box<ParameterType>,
+}
+
+impl ArrayType {
+    fn parse(schema: &Value, registry: &mut SchemaRegistry) -> Self {
+        let item = schema
+            .get("items")
+            .filter(|item| !item.is_null())
+            .map(|item| parse_type(item, registry))
+            .unwrap_or_else(|| ParameterType::Scalar(ScalarType::any()));
+        Self {
+            base: BaseType::new(schema, &["minItems", "maxItems"]),
+            item: Box::new(item),
+        }
+    }
+
+    fn to_typescript(&self, indent: &str, registry: &SchemaRegistry) -> String {
+        let inner_indent = format!("{indent}{INDENT}");
+        let docstring = self.item.format_docstring(&inner_indent);
+        let item = self.item.to_typescript(&inner_indent, registry);
+        if docstring.is_empty() {
+            format!("Array<{item}>")
+        } else {
+            format!("Array<\n{docstring}{inner_indent}{item}\n{indent}>")
+        }
+    }
+}
+
+struct EnumType {
+    base: BaseType,
+    values: Vec<Value>,
+}
+
+impl EnumType {
+    fn parse(schema: &Value) -> Self {
+        Self {
+            base: BaseType::new(schema, &[]),
+            values: schema
+                .get("enum")
+                .and_then(Value::as_array)
+                .cloned()
+                .unwrap_or_default(),
+        }
+    }
+
+    fn to_typescript(&self) -> String {
+        self.values
+            .iter()
+            .map(|value| match value {
+                Value::String(value) => format!("\"{value}\""),
+                Value::Null => "None".into(),
+                Value::Bool(true) => "True".into(),
+                Value::Bool(false) => "False".into(),
+                value => value.to_string(),
+            })
+            .collect::<Vec<_>>()
+            .join(" | ")
+    }
+}
+
+struct AnyOfType {
+    base: BaseType,
+    branches: Vec<ParameterType>,
+}
+
+impl AnyOfType {
+    fn parse(schema: &Value, registry: &mut SchemaRegistry) -> Self {
+        Self {
+            base: BaseType::new(schema, &[]),
+            branches: schema
+                .get("anyOf")
+                .and_then(Value::as_array)
+                .map(|branches| {
+                    branches
+                        .iter()
+                        .map(|branch| parse_type(branch, registry))
+                        .collect()
+                })
+                .unwrap_or_default(),
+        }
+    }
+
+    fn to_typescript(&self, indent: &str, registry: &SchemaRegistry) -> String {
+        self.branches
+            .iter()
+            .map(|branch| branch.to_typescript(indent, registry))
+            .collect::<Vec<_>>()
+            .join(" | ")
+    }
+}
+
+struct UnionType {
+    base: BaseType,
+    kinds: Vec<String>,
+}
+
+impl UnionType {
+    fn parse(schema: &Value) -> Self {
+        let kinds = schema
+            .get("type")
+            .and_then(Value::as_array)
+            .map(|kinds| {
+                kinds
+                    .iter()
+                    .filter_map(Value::as_str)
+                    .map(|kind| match kind {
+                        "integer" => "number".into(),
+                        "object" => "{}".into(),
+                        "array" => "Array<any>".into(),
+                        kind => kind.to_owned(),
+                    })
+                    .collect()
+            })
+            .unwrap_or_default();
+        Self {
+            base: BaseType::new(schema, &[]),
+            kinds,
+        }
+    }
+
+    fn to_typescript(&self) -> String {
+        self.kinds.join(" | ")
+    }
+}
+
+struct ReferenceType {
+    base: BaseType,
+    name: String,
+}
+
+impl ReferenceType {
+    fn parse(schema: &Value, registry: &mut SchemaRegistry) -> Self {
+        let reference = schema.get("$ref").and_then(Value::as_str).unwrap_or("");
+        let resolved = registry.resolve_reference(reference);
+        let name = match resolved {
+            Some(value) if value.get("$self_ref").and_then(Value::as_bool) == Some(true) => {
+                "parameters".into()
+            }
+            Some(_) => reference.rsplit('/').next().unwrap_or_default().into(),
+            None => "any".into(),
+        };
+        Self {
+            base: BaseType::new(schema, &[]),
+            name,
+        }
+    }
+
+    fn to_typescript(&self) -> String {
+        self.name.clone()
+    }
+}
+
+fn parse_type(schema: &Value, registry: &mut SchemaRegistry) -> ParameterType {
+    if registry.depth >= MAX_RECURSION_DEPTH {
+        return ParameterType::Scalar(ScalarType::any());
+    }
+    registry.depth += 1;
+    let result = parse_type_inner(schema, registry);
+    registry.depth -= 1;
+    result
+}
+
+fn parse_type_inner(schema: &Value, registry: &mut SchemaRegistry) -> ParameterType {
+    if let Some(schema) = schema.as_bool() {
+        return ParameterType::Scalar(ScalarType {
+            base: BaseType::default(),
+            kind: if schema { "any" } else { "null" }.into(),
+        });
+    }
+    let Some(object) = schema.as_object() else {
+        registry.unsupported = true;
+        return ParameterType::Scalar(ScalarType::any());
+    };
+    if object.contains_key("$ref") {
+        return ParameterType::Reference(ReferenceType::parse(schema, registry));
+    }
+    if object.contains_key("anyOf") {
+        return ParameterType::AnyOf(AnyOfType::parse(schema, registry));
+    }
+    if object.contains_key("enum") {
+        return ParameterType::Enum(EnumType::parse(schema));
+    }
+    if let Some(kind) = object.get("type") {
+        if kind.is_array() {
+            return ParameterType::Union(UnionType::parse(schema));
+        }
+        if let Some(kind) = kind.as_str() {
+            return match kind {
+                "object" => ParameterType::Object(ObjectType::parse(schema, registry)),
+                "array" => ParameterType::Array(ArrayType::parse(schema, registry)),
+                kind => ParameterType::Scalar(ScalarType::parse(kind, schema)),
+            };
+        }
+    }
+    if object.is_empty() {
+        return ParameterType::Scalar(ScalarType::any());
+    }
+    registry.unsupported = true;
+    ParameterType::Scalar(ScalarType::any())
+}
+
+fn format_description(description: &str, indent: &str) -> String {
+    description
+        .split('\n')
+        .map(|line| {
+            if line.is_empty() {
+                String::new()
+            } else {
+                format!("{indent}// {line}")
+            }
+        })
+        .collect::<Vec<_>>()
+        .join("\n")
+}
+
+fn json_inline(value: &Value) -> String {
+    match value {
+        Value::String(value) => value.clone(),
+        Value::Bool(value) => value.to_string(),
+        Value::Number(value) => value.to_string(),
+        Value::Null => "null".into(),
+        value => serde_json::to_string(value).unwrap_or_default(),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn recursively_sorts_tool_schema() {
+        let mut value = serde_json::json!({"z": [{"b": 1, "a": 2}], "a": 0});
+        deep_sort(&mut value);
+        assert_eq!(value.to_string(), r#"{"a":0,"z":[{"a":2,"b":1}]}"#);
+    }
+
+    #[test]
+    fn encodes_complex_schema_byte_exactly() {
+        let tools = serde_json::json!([{
+            "type": "function",
+            "function": {
+                "name": "weather",
+                "description": "Read weather",
+                "parameters": {
+                    "type": "object",
+                    "properties": {
+                        "units": {"type": "string", "enum": ["c", "f"]},
+                        "city": {"type": "string", "description": "City name"}
+                    },
+                    "required": ["city"]
+                }
+            }
+        }]);
+        assert_eq!(
+            encode_tools_to_typescript(tools.as_array().unwrap()).unwrap(),
+            "# Tools\n\n## functions\nnamespace functions {\n// Read weather\ntype weather = (_: {\n  // City name\n  city: string,\n  units?: \"c\" | \"f\"\n}) => any;\n}\n"
+        );
+    }
+
+    #[test]
+    fn unsupported_schema_uses_json_fallback() {
+        let tools = serde_json::json!([{
+            "type": "function",
+            "function": {
+                "name": "broken",
+                "parameters": {
+                    "type": "object",
+                    "properties": {"value": {"oneOf": [{"type": "string"}]}}
+                }
+            }
+        }]);
+        assert!(encode_tools_to_typescript(tools.as_array().unwrap()).is_none());
+    }
+
+    #[test]
+    fn null_default_is_omitted_like_checkpoint_python() {
+        let tools = serde_json::json!([{
+            "type": "function",
+            "function": {
+                "name": "optional_value",
+                "parameters": {
+                    "type": "object",
+                    "properties": {
+                        "value": {"type": ["string", "null"], "default": null}
+                    }
+                }
+            }
+        }]);
+        let encoded = encode_tools_to_typescript(tools.as_array().unwrap()).unwrap();
+        assert_eq!(
+            encoded,
+            "# Tools\n\n## functions\nnamespace functions {\ntype optional_value = (_: {\n  value?: string | null\n}) => any;\n}\n"
+        );
+        assert!(!encoded.contains("Default"));
+    }
+}

rust/sglang-renderer/src/preprocessing/tokenizer.rs

@@ -0,0 +1,602 @@
+//! Tokenizer primitives shared by renderer hosts.
+
+use crate::{
+    RendererError as Error, RendererLimits, SamplingParams, TextRequest, TokenIds, TokenIdsRequest,
+};
+use futures::channel::oneshot;
+use std::path::{Path, PathBuf};
+use std::sync::{Arc, Mutex};
+
+enum PoolJob {
+    Tokenize {
+        request: Box<TextRequest>,
+        reply: oneshot::Sender<Result<TokenIdsRequest, Error>>,
+    },
+    Stop,
+}
+
+struct TokenizerPoolInner {
+    jobs: flume::Sender<PoolJob>,
+    workers: Mutex<Vec<std::thread::JoinHandle<()>>>,
+}
+
+impl Drop for TokenizerPoolInner {
+    fn drop(&mut self) {
+        let workers = self.workers.get_mut().expect("tokenizer workers mutex");
+        for _ in 0..workers.len() {
+            let _ = self.jobs.send(PoolJob::Stop);
+        }
+        for worker in workers.drain(..) {
+            let _ = worker.join();
+        }
+    }
+}
+
+/// Bounded CPU tokenizer pool owned by renderer state.
+#[derive(Clone)]
+pub(crate) struct PooledTokenizer {
+    inner: Arc<TokenizerPoolInner>,
+}
+
+impl PooledTokenizer {
+    pub fn new(
+        tokenizer: Arc<dyn TextTokenizer>,
+        worker_count: usize,
+        queue_capacity: usize,
+    ) -> Self {
+        let worker_count = worker_count.max(1);
+        let (jobs, rx) = flume::bounded(queue_capacity.max(1));
+        let mut workers = Vec::with_capacity(worker_count);
+        for index in 0..worker_count {
+            let rx = rx.clone();
+            let tokenizer = tokenizer.clone();
+            workers.push(
+                std::thread::Builder::new()
+                    .name(format!("renderer-tokenizer-{index}"))
+                    .spawn(move || {
+                        while let Ok(job) = rx.recv() {
+                            match job {
+                                PoolJob::Tokenize { request, reply } => {
+                                    let result =
+                                        tokenize_text_request(*request, tokenizer.as_ref());
+                                    let _ = reply.send(result);
+                                }
+                                PoolJob::Stop => break,
+                            }
+                        }
+                    })
+                    .expect("spawn renderer tokenizer worker"),
+            );
+        }
+        Self {
+            inner: Arc::new(TokenizerPoolInner {
+                jobs,
+                workers: Mutex::new(workers),
+            }),
+        }
+    }
+}
+
+impl PooledTokenizer {
+    pub(crate) async fn tokenize(&self, request: TextRequest) -> Result<TokenIdsRequest, Error> {
+        let jobs = self.inner.jobs.clone();
+        let (reply, result) = oneshot::channel();
+        jobs.send_async(PoolJob::Tokenize {
+            request: Box::new(request),
+            reply,
+        })
+        .await
+        .map_err(|_| Error::Unavailable)?;
+        result.await.map_err(|_| Error::WorkerDropped)?
+    }
+}
+
+/// Pluggable text→token-ids backend. `Send + Sync` so one instance is shared
+/// (read-only) across all pinned workers.
+pub trait TextTokenizer: Send + Sync {
+    fn encode(&self, text: &str, add_special_tokens: bool) -> Result<TokenIds, Error>;
+
+    fn encode_segments(
+        &self,
+        segments: &[dynamo_tokenizers::EncodeSegment<'_>],
+        add_special_tokens: bool,
+    ) -> Result<TokenIds, Error> {
+        let text = segments
+            .iter()
+            .map(|segment| segment.text)
+            .collect::<String>();
+        self.encode(&text, add_special_tokens)
+    }
+}
+
+/// Load the tokenizer shared (Arc-backed) by the encode pool and detok shards.
+/// `tokenizer_path` is a tokenizer file, a model dir, or an HF Hub repo id
+/// (resolved from the local cache — no network).
+pub fn load_tokenizer(
+    tokenizer_path: Option<&str>,
+    revision: Option<&str>,
+    add_special_tokens: bool,
+) -> Result<dynamo_tokenizers::Tokenizer, String> {
+    let path =
+        tokenizer_path.ok_or_else(|| "no tokenizer configured: set tokenizer_path".to_string())?;
+    let file = resolve_tokenizer_file(path, revision).ok_or_else(|| {
+        format!(
+            "no supported tokenizer file found for '{path}' (expected tokenizer.json, tiktoken.model, or *.tiktoken)"
+        )
+    })?;
+    let tokenizer = dynamo_tokenizers::Tokenizer::from_file_with_options(
+        &file,
+        dynamo_tokenizers::TokenizerOptions { add_special_tokens },
+    )
+    .map_err(|e| format!("tokenizer load failed ({file}): {e}"))?;
+    tracing::info!(%path, "loaded tokenizer");
+    Ok(tokenizer)
+}
+
+/// Resolve the tokenizer source used by the renderer.
+pub fn resolve_tokenizer_file(path: &str, revision: Option<&str>) -> Option<String> {
+    let input = Path::new(path);
+    if input.is_file() && is_supported_tokenizer_file(input) {
+        return Some(input.to_string_lossy().into_owned());
+    }
+    let directory = model_directory(path, revision)?;
+    discover_tokenizer_in_dir(&directory).map(|path| path.to_string_lossy().into_owned())
+}
+
+/// Resolve a dedicated Hugging Face chat-template file when the template is
+/// not embedded in `tokenizer_config.json`.
+pub fn resolve_chat_template_file(path: &str, revision: Option<&str>) -> Option<String> {
+    let directory = model_directory(path, revision)?;
+    discover_chat_template_in_dir(&directory).map(|path| path.to_string_lossy().into_owned())
+}
+
+fn model_directory(path: &str, revision: Option<&str>) -> Option<PathBuf> {
+    let input = Path::new(path);
+    if input.is_dir() {
+        return Some(input.to_path_buf());
+    }
+    if input.is_file() {
+        return input.parent().map(Path::to_path_buf);
+    }
+    let repo = cache_repo(path, revision);
+    [
+        "config.json",
+        "tokenizer_config.json",
+        "tokenizer.json",
+        "tiktoken.model",
+    ]
+    .into_iter()
+    .find_map(|name| repo.get(name))
+    .and_then(|file| file.parent().map(Path::to_path_buf))
+}
+
+fn discover_tokenizer_in_dir(directory: &Path) -> Option<PathBuf> {
+    let tokenizer_config = directory.join("tokenizer_config.json");
+    let prefers_tiktoken = std::fs::read_to_string(tokenizer_config)
+        .ok()
+        .and_then(|text| serde_json::from_str::<serde_json::Value>(&text).ok())
+        .and_then(|config| {
+            config
+                .get("tokenizer_class")
+                .and_then(serde_json::Value::as_str)
+                .map(|class| class.to_ascii_lowercase().contains("tiktoken"))
+        })
+        .unwrap_or(false);
+    let hugging_face = directory.join("tokenizer.json");
+    let tiktoken = directory.join("tiktoken.model");
+    let discovered_tiktoken = || {
+        sorted_directory_files(directory).find(|path| {
+            path.file_name()
+                .and_then(|name| name.to_str())
+                .is_some_and(|name| name.ends_with(".tiktoken"))
+        })
+    };
+    if prefers_tiktoken {
+        tiktoken
+            .is_file()
+            .then_some(tiktoken)
+            .or_else(discovered_tiktoken)
+            .or_else(|| hugging_face.is_file().then_some(hugging_face))
+    } else {
+        hugging_face
+            .is_file()
+            .then_some(hugging_face)
+            .or_else(|| tiktoken.is_file().then_some(tiktoken))
+            .or_else(discovered_tiktoken)
+    }
+}
+
+fn discover_chat_template_in_dir(directory: &Path) -> Option<PathBuf> {
+    for name in ["chat_template.json", "chat_template.jinja"] {
+        let candidate = directory.join(name);
+        if candidate.is_file() {
+            return Some(candidate);
+        }
+    }
+    sorted_directory_files(directory).find(|path| {
+        path.file_name()
+            .and_then(|name| name.to_str())
+            .is_some_and(|name| name.ends_with(".jinja"))
+    })
+}
+
+fn sorted_directory_files(directory: &Path) -> impl Iterator<Item = PathBuf> {
+    let mut files = std::fs::read_dir(directory)
+        .ok()
+        .into_iter()
+        .flatten()
+        .flatten()
+        .map(|entry| entry.path())
+        .filter(|path| path.is_file())
+        .collect::<Vec<_>>();
+    files.sort();
+    files.into_iter()
+}
+
+fn is_supported_tokenizer_file(path: &Path) -> bool {
+    path.file_name()
+        .and_then(|name| name.to_str())
+        .is_some_and(|name| {
+            name == "tokenizer.json" || name == "tiktoken.model" || name.ends_with(".tiktoken")
+        })
+}
+
+/// Resolve a model file from the tokenizer source: a dir → `dir/<file>`, a file →
+/// its sibling, else an HF Hub repo id → the local cache. `None` if not found.
+pub fn resolve_model_file(path: &str, revision: Option<&str>, filename: &str) -> Option<String> {
+    let p = Path::new(path);
+    if p.is_dir() {
+        let f = p.join(filename);
+        return f.is_file().then(|| f.to_string_lossy().into_owned());
+    }
+    if p.is_file() {
+        // `path` is a file (e.g. `tokenizer.json`); look for the sibling.
+        let f = p.parent()?.join(filename);
+        return f.is_file().then(|| f.to_string_lossy().into_owned());
+    }
+    // Not a local path → HF Hub repo id (offline cache lookup).
+    resolve_from_hub_cache(path, revision, filename)
+}
+
+/// Locate a file for an HF Hub repo id in the local cache. Offline —
+/// the scheduler pre-downloads the model. `None` if not cached.
+fn resolve_from_hub_cache(repo_id: &str, revision: Option<&str>, filename: &str) -> Option<String> {
+    cache_repo(repo_id, revision)
+        .get(filename)
+        .map(|p| p.to_string_lossy().into_owned())
+}
+
+fn cache_repo(repo_id: &str, revision: Option<&str>) -> hf_hub::CacheRepo {
+    use hf_hub::{Cache, Repo, RepoType};
+
+    // Python resolves the cache dir as HF_HUB_CACHE > HUGGINGFACE_HUB_CACHE >
+    // HF_HOME/hub > ~/.cache/huggingface/hub; the hf-hub crate only knows
+    // HF_HOME. Honor the explicit cache-dir overrides first, or the Rust
+    // server misses models the Python scheduler already downloaded.
+    let cache = ["HF_HUB_CACHE", "HUGGINGFACE_HUB_CACHE"]
+        .iter()
+        .find_map(|var| std::env::var(var).ok())
+        .map(|dir| Cache::new(dir.into()))
+        .unwrap_or_else(Cache::from_env);
+    cache.repo(Repo::with_revision(
+        repo_id.to_string(),
+        RepoType::Model,
+        revision.unwrap_or("main").to_string(),
+    ))
+}
+
+/// Real tokenizer over two already-loaded dynamo handles. Dynamo fixes
+/// `add_special_tokens` when loading, so selecting the mode at request time
+/// requires one handle for each setting.
+pub struct DynamoTokenizer {
+    without_specials: dynamo_tokenizers::Tokenizer,
+    with_specials: dynamo_tokenizers::Tokenizer,
+}
+
+impl DynamoTokenizer {
+    pub fn new(
+        without_specials: dynamo_tokenizers::Tokenizer,
+        with_specials: dynamo_tokenizers::Tokenizer,
+    ) -> Self {
+        Self {
+            without_specials,
+            with_specials,
+        }
+    }
+}
+
+impl TextTokenizer for DynamoTokenizer {
+    fn encode(&self, text: &str, add_special_tokens: bool) -> Result<TokenIds, Error> {
+        let encoding = if add_special_tokens {
+            &self.with_specials
+        } else {
+            &self.without_specials
+        }
+        .encode(text)
+        .map_err(|e| Error::Tokenize(e.to_string()))?;
+        // Vocab ids are non-negative and fit in i32.
+        Ok(encoding.token_ids().iter().map(|&id| id as i32).collect())
+    }
+
+    fn encode_segments(
+        &self,
+        segments: &[dynamo_tokenizers::EncodeSegment<'_>],
+        add_special_tokens: bool,
+    ) -> Result<TokenIds, Error> {
+        let encoding = if add_special_tokens {
+            &self.with_specials
+        } else {
+            &self.without_specials
+        }
+        .encode_segments(segments)
+        .map_err(|error| Error::Tokenize(error.to_string()))?;
+        Ok(encoding.token_ids().iter().map(|&id| id as i32).collect())
+    }
+}
+
+fn resolve_stop_token_window(sampling_params: &mut SamplingParams, tokenizer: &dyn TextTokenizer) {
+    // Size the scheduler's stop-match window in TOKENS, as Python's
+    // `normalize(tokenizer)` does.
+    if let Some(stop_tokens) = sampling_params
+        .stop_strs
+        .iter()
+        // A stop that won't encode falls back to its byte length rather
+        // than failing the request: still an over-estimate, never an
+        // under-estimate, so the scheduler cannot miss that stop.
+        .map(|stop| {
+            tokenizer
+                .encode(stop, false)
+                .map_or(stop.len(), |ids| ids.len())
+        })
+        .max()
+    {
+        sampling_params.stop_str_max_len = stop_tokens;
+    }
+}
+
+/// Convert a text input into the token-ID request consumed by shared
+/// post-tokenization preparation.
+pub fn tokenize_text_request(
+    request: TextRequest,
+    tokenizer: &dyn TextTokenizer,
+) -> Result<TokenIdsRequest, Error> {
+    let TextRequest {
+        rid,
+        prompt,
+        add_special_tokens,
+        mut options,
+        metadata,
+    } = request;
+    resolve_stop_token_window(&mut options.sampling_params, tokenizer);
+    let input_ids = match prompt.encode_segments() {
+        Some(segments) => tokenizer.encode_segments(&segments, add_special_tokens)?,
+        None => tokenizer.encode(prompt.as_str(), add_special_tokens)?,
+    };
+    Ok(TokenIdsRequest {
+        rid,
+        input_ids,
+        options,
+        metadata,
+    })
+}
+
+/// Validate fields that must be safe before tokenization or engine submission.
+pub fn validate_text_request(request: &TextRequest, limits: &RendererLimits) -> Result<(), Error> {
+    validate_request_id(&request.rid)?;
+    if request.prompt.as_str().is_empty() {
+        return Err(Error::Validation("prompt cannot be empty".into()));
+    }
+    let options = &request.options;
+    validate_completion_fields(
+        None,
+        options.token_ids_logprob.as_deref(),
+        options.return_hidden_states,
+        limits,
+    )
+}
+
+/// Validate an already-tokenized request without passing it through the text
+/// tokenizer path.
+pub fn validate_token_ids_request(
+    request: &TokenIdsRequest,
+    limits: &RendererLimits,
+) -> Result<(), Error> {
+    validate_request_id(&request.rid)?;
+    if request.input_ids.is_empty() {
+        return Err(Error::Validation("input_ids cannot be empty".into()));
+    }
+    let options = &request.options;
+    validate_completion_fields(
+        Some(&request.input_ids),
+        options.token_ids_logprob.as_deref(),
+        options.return_hidden_states,
+        limits,
+    )
+}
+
+pub(crate) fn validate_request_id(rid: &str) -> Result<(), Error> {
+    if rid.len() > 128 {
+        return Err(Error::Validation(format!(
+            "rid is {} bytes, over the 128-byte limit",
+            rid.len()
+        )));
+    }
+    Ok(())
+}
+
+/// Validate the common completion fields before tokenization or engine
+/// submission. Request identity remains an enclosing host concern.
+pub fn validate_completion_fields(
+    input_ids: Option<&[i32]>,
+    token_ids_logprob: Option<&[i32]>,
+    return_hidden_states: bool,
+    limits: &RendererLimits,
+) -> Result<(), Error> {
+    for &id in input_ids.iter().flat_map(|ids| ids.iter()) {
+        if id < 0 || id as u64 >= limits.vocab_size {
+            return Err(Error::Validation(format!(
+                "input_ids contains out-of-vocabulary token id {id}; valid range is [0, {})",
+                limits.vocab_size
+            )));
+        }
+    }
+    for &id in token_ids_logprob.iter().flat_map(|ids| ids.iter()) {
+        if id < 0 || id as u64 >= limits.vocab_size {
+            return Err(Error::Validation(format!(
+                "token_ids_logprob contains out-of-vocabulary token id {id}; valid range is [0, {})",
+                limits.vocab_size
+            )));
+        }
+    }
+    if return_hidden_states && !limits.enable_return_hidden_states {
+        return Err(Error::Validation(
+            "The server is not configured to return the hidden states. Please set `--enable-return-hidden-states` to enable this feature."
+                .into(),
+        ));
+    }
+    Ok(())
+}
+
+/// Enforce the model context limit after tokenization.
+pub fn check_total_tokens(
+    request: &mut TokenIdsRequest,
+    limits: &RendererLimits,
+) -> Result<(), Error> {
+    let mut input_ids = Some(std::mem::take(&mut request.input_ids));
+    let result =
+        check_completion_token_budget(&mut input_ids, &mut request.options.sampling_params, limits);
+    request.input_ids = input_ids.expect("validated token-ID request retains input_ids");
+    result
+}
+
+/// Enforce the context limit over the common token-only completion fields.
+pub fn check_completion_token_budget(
+    input_ids: &mut Option<TokenIds>,
+    sampling_params: &mut SamplingParams,
+    limits: &RendererLimits,
+) -> Result<(), Error> {
+    let max_req_len = limits.context_len;
+    let input_len = input_ids.as_ref().map_or(0, Vec::len) as u64 + limits.num_reserved_tokens;
+    if input_len >= max_req_len {
+        if !limits.allow_auto_truncate {
+            return Err(Error::Validation(format!(
+                "The input ({input_len} tokens) is longer than the model's context length ({max_req_len} tokens)."
+            )));
+        }
+        if let Some(ids) = input_ids {
+            ids.truncate(max_req_len as usize);
+        }
+    }
+    let input_len = input_ids.as_ref().map_or(0, Vec::len) as u64 + limits.num_reserved_tokens;
+    let Some(max_new_tokens) = sampling_params.max_new_tokens else {
+        return Ok(());
+    };
+    let total = input_len.saturating_add(max_new_tokens.max(0) as u64);
+    if total <= max_req_len {
+        return Ok(());
+    }
+    if !limits.allow_auto_truncate {
+        return Err(Error::Validation(format!(
+            "Requested token count exceeds the model's maximum context length of {max_req_len} tokens. You requested a total of {total} tokens: {input_len} tokens from the input messages and {max_new_tokens} tokens for the completion. Please reduce the number of tokens in the input messages or the completion to fit within the limit."
+        )));
+    }
+    let clamped = max_req_len.saturating_sub(input_len) as i64;
+    if sampling_params.min_new_tokens > clamped {
+        return Err(Error::Validation(format!(
+            "min_new_tokens must be in [0, max_new_tokens({clamped})], got {}",
+            sampling_params.min_new_tokens
+        )));
+    }
+    sampling_params.max_new_tokens = Some(clamped);
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use std::sync::atomic::{AtomicU64, Ordering};
+
+    use dynamo_renderer::{RenderedPrompt, RenderedSegment};
+
+    use super::*;
+    use crate::GenerationOptions;
+
+    static NEXT_TEMP_DIR: AtomicU64 = AtomicU64::new(0);
+
+    fn temp_model_dir(label: &str) -> PathBuf {
+        let sequence = NEXT_TEMP_DIR.fetch_add(1, Ordering::Relaxed);
+        let path = std::env::temp_dir().join(format!(
+            "sglang-renderer-{label}-{}-{sequence}",
+            std::process::id()
+        ));
+        std::fs::create_dir_all(&path).unwrap();
+        path
+    }
+
+    #[test]
+    fn model_discovery_finds_tiktoken_and_dedicated_chat_template() {
+        let directory = temp_model_dir("model-files");
+        std::fs::write(
+            directory.join("tokenizer_config.json"),
+            r#"{"tokenizer_class":"KimiTikTokenTokenizer"}"#,
+        )
+        .unwrap();
+        std::fs::write(directory.join("tokenizer.json"), "{}").unwrap();
+        std::fs::write(directory.join("tokenizer.tiktoken"), "token").unwrap();
+        std::fs::write(directory.join("chat_template.jinja"), "{{ messages }}").unwrap();
+
+        assert_eq!(
+            resolve_tokenizer_file(directory.to_str().unwrap(), None),
+            Some(
+                directory
+                    .join("tokenizer.tiktoken")
+                    .to_string_lossy()
+                    .into_owned()
+            )
+        );
+        assert_eq!(
+            resolve_chat_template_file(directory.to_str().unwrap(), None),
+            Some(
+                directory
+                    .join("chat_template.jinja")
+                    .to_string_lossy()
+                    .into_owned()
+            )
+        );
+
+        std::fs::remove_dir_all(directory).unwrap();
+    }
+
+    struct SegmentTokenizer;
+
+    impl TextTokenizer for SegmentTokenizer {
+        fn encode(&self, _text: &str, _add_special_tokens: bool) -> Result<TokenIds, Error> {
+            Ok(vec![9])
+        }
+
+        fn encode_segments(
+            &self,
+            segments: &[dynamo_tokenizers::EncodeSegment<'_>],
+            _add_special_tokens: bool,
+        ) -> Result<TokenIds, Error> {
+            Ok(segments
+                .iter()
+                .map(|segment| if segment.allow_special { 1 } else { 2 })
+                .collect())
+        }
+    }
+
+    #[test]
+    fn rendered_prompt_preserves_segment_boundaries_until_tokenization() {
+        let prompt = RenderedPrompt::segmented(vec![
+            RenderedSegment::new("<control>", true),
+            RenderedSegment::new("user text", false),
+        ]);
+        let tokenized = tokenize_text_request(
+            TextRequest::rendered("request", prompt, false, GenerationOptions::default()),
+            &SegmentTokenizer,
+        )
+        .unwrap();
+
+        assert_eq!(tokenized.input_ids, [1, 2]);
+    }
+}

rust/sglang-renderer/src/runtime.rs

@@ -0,0 +1,96 @@
+//! Renderer process state and HTTP listener.
+
+use std::net::SocketAddr;
+use std::sync::Arc;
+
+use crate::{DynamoTokenizer, RendererConfig, RendererService, TextTokenizer, load_tokenizer};
+
+use crate::engine::{GenerationService, HttpGenerateClient, TokenDecoder};
+use crate::frontend::http::{hosted_routes, render_only_routes, standalone_routes};
+use crate::openai::OpenAIService;
+
+#[derive(Clone, Debug)]
+pub struct RendererRuntimeConfig {
+    pub http_addr: SocketAddr,
+    pub http_workers: usize,
+    pub tokenizer_workers: usize,
+    pub queue_capacity: usize,
+    /// Optional SGLang engine origin. When absent, inference routes are not mounted.
+    pub engine_url: Option<String>,
+    /// Proxy routes not owned by the renderer to `engine_url`.
+    pub proxy_unhandled_routes: bool,
+    pub renderer: RendererConfig,
+}
+
+pub async fn serve(config: RendererRuntimeConfig) -> Result<(), String> {
+    let mode = match (&config.engine_url, config.proxy_unhandled_routes) {
+        (None, false) => "render-only",
+        (Some(_), false) => "serving",
+        (Some(_), true) => "hosted",
+        (None, true) => return Err("proxy_unhandled_routes requires engine_url".to_string()),
+    };
+    let tokenizer_without_specials = load_tokenizer(
+        (!config.renderer.tokenizer_path.is_empty())
+            .then_some(config.renderer.tokenizer_path.as_str()),
+        config.renderer.revision.as_deref(),
+        false,
+    )?;
+    let tokenizer_with_specials = load_tokenizer(
+        (!config.renderer.tokenizer_path.is_empty())
+            .then_some(config.renderer.tokenizer_path.as_str()),
+        config.renderer.revision.as_deref(),
+        true,
+    )?;
+    let encode_tokenizer: Arc<dyn TextTokenizer> = Arc::new(DynamoTokenizer::new(
+        tokenizer_without_specials.clone(),
+        tokenizer_with_specials,
+    ));
+    let renderer = Arc::new(RendererService::with_tokenizer(
+        config.renderer,
+        encode_tokenizer,
+        config.tokenizer_workers,
+        config.queue_capacity,
+    ));
+    let app = match (config.engine_url, config.proxy_unhandled_routes) {
+        (None, false) => render_only_routes(renderer),
+        (Some(engine_url), false) => {
+            let generate_client = HttpGenerateClient::new(engine_url)?;
+            standalone_routes(
+                OpenAIService::new(
+                    renderer,
+                    GenerationService::new(
+                        Arc::new(generate_client.clone()),
+                        TokenDecoder::new(tokenizer_without_specials),
+                    ),
+                ),
+                generate_client,
+            )
+        }
+        (Some(engine_url), true) => {
+            let generate_client = HttpGenerateClient::new(&engine_url)?;
+            hosted_routes(
+                OpenAIService::new(
+                    renderer,
+                    GenerationService::new(
+                        Arc::new(generate_client),
+                        TokenDecoder::new(tokenizer_without_specials),
+                    ),
+                ),
+                engine_url,
+            )?
+        }
+        (None, true) => unreachable!("runtime topology was validated above"),
+    };
+    let listener = tokio::net::TcpListener::bind(config.http_addr)
+        .await
+        .map_err(|error| format!("binding renderer on {} failed: {error}", config.http_addr))?;
+    tracing::info!(address = %config.http_addr, mode, "renderer listening");
+    axum::serve(listener, app.into_make_service())
+        .with_graceful_shutdown(async {
+            if let Err(error) = tokio::signal::ctrl_c().await {
+                tracing::error!(%error, "installing renderer shutdown signal failed");
+            }
+        })
+        .await
+        .map_err(|error| format!("renderer HTTP server failed: {error}"))
+}

rust/sglang-renderer/src/types.rs

@@ -0,0 +1,12 @@
+//! Renderer request primitives.
+
+use serde::{Deserialize, Serialize};
+
+pub type TokenIds = Vec<i32>;
+
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[serde(untagged)]
+pub enum OneOrMany<T> {
+    One(T),
+    Many(Vec<T>),
+}

rust/sglang-renderer/tests/public_preprocessing.rs

@@ -0,0 +1,104 @@
+use std::sync::{Arc, Mutex};
+
+use dynamo_protocols::types::ChatCompletionRequestMessage;
+use sglang_renderer::{
+    ChatRequest, GenerateRequestMetadata, GenerationOptions, RendererConfig, RendererError,
+    RendererLimits, RendererService, SamplingDefaults, SamplingParams, TextRequest, TextTokenizer,
+};
+
+#[derive(Clone, Default)]
+struct RecordingTokenizer {
+    prompts: Arc<Mutex<Vec<(String, bool)>>>,
+}
+
+impl TextTokenizer for RecordingTokenizer {
+    fn encode(&self, text: &str, add_special_tokens: bool) -> Result<Vec<i32>, RendererError> {
+        self.prompts
+            .lock()
+            .unwrap()
+            .push((text.to_owned(), add_special_tokens));
+        Ok(vec![7])
+    }
+}
+
+fn config() -> RendererConfig {
+    RendererConfig {
+        served_model_name: "model".into(),
+        tokenizer_path: ".".into(),
+        revision: None,
+        model_path: String::new(),
+        chat_template: Some("chatml".into()),
+        tool_call_parser: None,
+        reasoning_parser: None,
+        default_chat_template_kwargs: Default::default(),
+        stream_response_default_include_usage: false,
+        default_sampling_params: SamplingDefaults::default(),
+        limits: RendererLimits {
+            vocab_size: 128,
+            context_len: 128,
+            num_reserved_tokens: 0,
+            allow_auto_truncate: false,
+            enable_return_hidden_states: false,
+        },
+    }
+}
+
+#[test]
+fn completion_and_chat_share_the_public_text_preparation_boundary() {
+    let tokenizer = RecordingTokenizer::default();
+    let prompts = tokenizer.prompts.clone();
+    let renderer = RendererService::with_tokenizer(config(), Arc::new(tokenizer), 1, 8);
+
+    let completion = TextRequest::text(
+        "completion-0",
+        "plain completion",
+        true,
+        GenerationOptions {
+            sampling_params: SamplingParams {
+                max_new_tokens: Some(1),
+                ..Default::default()
+            },
+            ..Default::default()
+        },
+    );
+    futures::executor::block_on(renderer.prepare_text_requests(vec![completion])).unwrap();
+
+    let messages: Vec<ChatCompletionRequestMessage> = serde_json::from_value(serde_json::json!([
+        {"role": "user", "content": "hello"}
+    ]))
+    .unwrap();
+    let chat = ChatRequest {
+        rid: "chat".into(),
+        model: "model".into(),
+        messages,
+        tools: None,
+        tool_choice: None,
+        response_format: None,
+        reasoning_effort: None,
+        continue_final_message: false,
+        chat_template_args: None,
+        sampling_params: SamplingParams {
+            max_new_tokens: Some(1),
+            ..Default::default()
+        },
+        choice_count: 1,
+        stream: false,
+        return_logprob: false,
+        top_logprobs_num: 0,
+        parallel_tool_calls: true,
+        metadata: GenerateRequestMetadata::default(),
+    };
+    futures::executor::block_on(renderer.prepare_chat(chat)).unwrap();
+
+    let prompts = prompts.lock().unwrap();
+    assert!(
+        prompts
+            .iter()
+            .any(|(text, add_special_tokens)| text == "plain completion" && *add_special_tokens)
+    );
+    assert!(
+        prompts
+            .iter()
+            .any(|(text, add_special_tokens)| text.contains("hello") && !add_special_tokens)
+    );
+}

rust/sglang-renderer/tests/render_only_cli.rs

@@ -0,0 +1,122 @@
+// Keep the inner attribute off the first line so shebang lint does not misclassify it.
+#![cfg(feature = "http")]
+
+use std::process::{Child, Command, Stdio};
+use std::time::{Duration, Instant};
+
+use reqwest::StatusCode;
+use serde_json::{Value, json};
+
+struct ChildGuard(Child);
+
+struct TestDirectory(std::path::PathBuf);
+
+impl Drop for ChildGuard {
+    fn drop(&mut self) {
+        let _ = self.0.kill();
+        let _ = self.0.wait();
+    }
+}
+
+impl Drop for TestDirectory {
+    fn drop(&mut self) {
+        let _ = std::fs::remove_dir_all(&self.0);
+    }
+}
+
+fn available_port() -> u16 {
+    let listener = std::net::TcpListener::bind("127.0.0.1:0").unwrap();
+    listener.local_addr().unwrap().port()
+}
+
+async fn wait_until_ready(child: &mut Child, client: &reqwest::Client, health_url: &str) {
+    let deadline = Instant::now() + Duration::from_secs(10);
+    loop {
+        if let Some(status) = child.try_wait().unwrap() {
+            panic!("render-only process exited during startup with {status}");
+        }
+        if client
+            .get(health_url)
+            .send()
+            .await
+            .is_ok_and(|response| response.status() == StatusCode::OK)
+        {
+            return;
+        }
+        assert!(
+            Instant::now() < deadline,
+            "render-only process did not start"
+        );
+        tokio::time::sleep(Duration::from_millis(25)).await;
+    }
+}
+
+#[tokio::test]
+async fn binary_starts_without_an_engine_and_serves_only_preprocessing() {
+    let source_tokenizer = std::path::Path::new(env!("CARGO_MANIFEST_DIR"))
+        .join("../../experimental/sgl-router/tests/fixtures/tiny_tokenizer.json");
+    let model = TestDirectory(
+        std::env::temp_dir().join(format!("sglang-render-only-{}", uuid::Uuid::new_v4())),
+    );
+    std::fs::create_dir(&model.0).unwrap();
+    std::fs::copy(source_tokenizer, model.0.join("tokenizer.json")).unwrap();
+    let port = available_port();
+    let mut child = ChildGuard(
+        Command::new(env!("CARGO_BIN_EXE_sglang-renderer"))
+            .arg(&model.0)
+            .arg("--tokenizer-path")
+            .arg(&model.0)
+            .arg("--served-model-name")
+            .arg("model")
+            .arg("--resolved-sampling-params")
+            .arg("{}")
+            .arg("--context-length")
+            .arg("64")
+            .arg("--vocab-size")
+            .arg("512")
+            .arg("--host")
+            .arg("127.0.0.1")
+            .arg("--port")
+            .arg(port.to_string())
+            .stdout(Stdio::null())
+            .stderr(Stdio::inherit())
+            .spawn()
+            .unwrap(),
+    );
+    let client = reqwest::Client::builder().no_proxy().build().unwrap();
+    let origin = format!("http://127.0.0.1:{port}");
+    wait_until_ready(&mut child.0, &client, &format!("{origin}/health")).await;
+
+    let tokenized = client
+        .post(format!("{origin}/v1/tokenize"))
+        .json(&json!({"prompt": "hello"}))
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(tokenized.status(), StatusCode::OK);
+    let tokenized: Value = tokenized.json().await.unwrap();
+    assert!(tokenized["count"].as_u64().is_some_and(|count| count > 0));
+
+    let completion = json!({"model": "model", "prompt": "hello"});
+    let rendered = client
+        .post(format!("{origin}/v1/completions/render"))
+        .json(&completion)
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(rendered.status(), StatusCode::OK);
+    let rendered: Value = rendered.json().await.unwrap();
+    assert!(
+        rendered
+            .as_array()
+            .is_some_and(|requests| requests.len() == 1)
+    );
+
+    let inference = client
+        .post(format!("{origin}/v1/completions"))
+        .json(&completion)
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(inference.status(), StatusCode::NOT_FOUND);
+}