[sgl-router] Rename chat encoder to chat formatter (#39459)

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

experimental/sgl-router/tests/proxy/sticky_input_ids.rs

@@ -3,8 +3,8 @@
 
 //! Tokenize-once at ingress under the STICKY policy. The engine-tokenization
 //! offload (`input_ids` forwarding) is a property of the MODEL — does it have a
-//! chat encoder? — not of the routing policy, so a sticky-routed request on a
-//! chat-encoder model must forward `input_ids` exactly like cache-aware does,
+//! chat formatter? — not of the routing policy, so a sticky-routed request on a
+//! chat-formatter model must forward `input_ids` exactly like cache-aware does,
 //! while still pinning sessions O(1) by header.
 //!
 //! Asserts through the real chat handler + `MockWorker` backends:
@@ -17,7 +17,7 @@
 //!   routing is unchanged by the added tokenization).
 //!
 //! The model id contains `deepseek-v4` so the tokenizer registry auto-attaches
-//! the built-in V4 chat encoder — the engine-equivalent path — without a
+//! the built-in V4 chat formatter — the engine-equivalent path — without a
 //! template fixture.
 
 use axum::body::Body;
@@ -82,14 +82,14 @@ fn config() -> Config {
 
 /// Build an `AppContext` running the sticky policy over the given workers.
 /// The tokenizer registry is loaded from config (real tiny tokenizer + the
-/// auto-attached V4 chat encoder) so the ingress can tokenize — the sticky
+/// auto-attached V4 chat formatter) so the ingress can tokenize — the sticky
 /// policy itself holds no tokenizer.
 fn build_ctx(worker_urls: &[String]) -> Arc<AppContext> {
     let cfg = config();
     let tokenizers = Arc::new(TokenizerRegistry::load_from_config(&cfg).unwrap());
     assert!(
-        tokenizers.has_chat_encoder(MODEL),
-        "deepseek-v4 model id must auto-attach the built-in chat encoder"
+        tokenizers.has_chat_formatter(MODEL),
+        "deepseek-v4 model id must auto-attach the built-in chat formatter"
     );
     let registry = Arc::new(WorkerRegistry::default());
     for (i, url) in worker_urls.iter().enumerate() {