config: resolution declares, and nothing writes a field (#36618)

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

python/sglang/srt/arg_groups/overrides.py

@@ -190,10 +190,8 @@ def resolving_view(server_args: Any) -> ResolvingConfig:
     return ResolvingConfig(server_args)
 
 
-# Ordered post-process passes (the normalization stage). List order is the
-# end-state execution order and mirrors today's handler call sequence in
-# __post_init__; during the transition each pass is invoked from its legacy
-# slot via run_post_process_pass, so ordering is preserved byte-for-byte.
+# Registered post-process passes. This is a registry, not an execution order:
+# each pass is invoked from its own slot via run_post_process_pass.
 POST_PROCESS_PASSES: List[Callable[..., dict]] = []
 
 
@@ -223,11 +221,29 @@ def run_post_process_pass(server_args: Any, fn: Callable[..., dict]) -> None:
 
     Evaluates the pass on the resolving state (a read-only view with the
     accumulated declarations overlaid from the stash) and appends its
-    declaration to the stash. During ``__post_init__`` the fields stay
-    untouched: the stash is what the config bags are projected from. A pass
-    invoked after resolution finished (a post-init slot) writes through
-    immediately, because there is no later projection to pick it up.
+    declaration to the stash, which is what the config bags are projected from.
+    The fields stay untouched.
+
+    A slot that runs after resolution -- ``check_server_args`` hosts one -- lands
+    in the same stash, which publish projects from later, so it needs no field
+    write either. After *publish* there is no such later projection: the stash
+    would grow an entry nothing reads. So, like ``declare_late_resolution``,
+    this refuses the published record -- post-publish changes go to the bags
+    through ``get_context().override(...)``.
     """
+    from sglang.srt.runtime_context import get_context
+
+    try:
+        published = get_context().server_args
+    except ValueError:
+        published = None
+    if published is server_args:
+        raise ValueError(
+            f"run_post_process_pass({fn.__qualname__!r}) called on the published "
+            "config; the stash is projected at publish and never again, so a "
+            "declaration made here would be a silent no-op -- post-publish "
+            "changes go to the bags via get_context().override(...)"
+        )
     declared = fn(ResolvedView(server_args, overlay=_declaration_overlay(server_args)))
     if not isinstance(declared, dict):
         raise TypeError(
@@ -246,13 +262,15 @@ def run_post_process_pass(server_args: Any, fn: Callable[..., dict]) -> None:
             stash = server_args._resolved_overrides = []
         stash.append(entry)
         validate_declarations(server_args, [entry])
-        if getattr(server_args, "_resolution_finished", False):
-            _apply_fields(server_args, declared)
 
 
 def _apply_fields(server_args: Any, fields: Dict[str, Any]) -> None:
-    """Write fields on behalf of the pipeline (bypasses the strict bare-
-    assignment guard that protects post-resolution mutation)."""
+    """Write record fields past the guard that forbids post-resolution writes.
+
+    Resolution declares, so nothing in the pipeline calls this. It exists for
+    ``RuntimeContext.override_server_args``, the launch stand-in tests use: there
+    the caller's values are both the operator's input and resolution's answer.
+    """
     object.__setattr__(server_args, "_internal_write", True)
     try:
         for field, value in fields.items():
@@ -1745,9 +1763,7 @@ def _step3p_overrides(server_args: Any, hf_config: Any) -> dict:
 
 
 # ---------------------------------------------------------------------------
-# Post-process passes (normalization stage), in end-state execution order.
-# Faithful ports of the legacy __post_init__ handlers; each is invoked from
-# its legacy slot via run_post_process_pass during the transition.
+# Post-process passes (normalization stage).
 # ---------------------------------------------------------------------------
 
 
@@ -2803,6 +2819,7 @@ def _moe_runner_fusion_disable(view: Any) -> dict:
     return {}
 
 
+@register_post_process
 def _a2a_fusion_adjustments(view: Any) -> dict:
     """A2A-backend-driven shared-experts fusion adjustments, declared at the
     legacy write slots in _handle_a2a_moe: Waterfill requires the
@@ -2982,6 +2999,7 @@ def validate_declarations(
             )
 
 
+@register_post_process
 def _hrm_text_attention_force(view: Any) -> dict:
     """HRM-Text's bidirectional prefix attention only works on the Triton
     backend. Invoked as the last attention declaration of the resolution