fix(type-checking): satisfy the basedpyright budget gate for auto-router compression

Two fixes for the zero-headroom basedpyright budget:

- arm_pre_call's data parameter is dict[str, object], not MutableMapping: the
  latter is itself banned by LIT001 with no benefit, and it mismatched every
  dict-typed helper (get_or_create_metadata_bucket, resolve_structured_messages,
  _get_tags_from_request_kwargs), which is what the budget was actually flagging.
- Router.async_pre_routing_hook computed pre_routing_hook_response in one shot
  instead of reassigning a Final-annotated local.

The remaining two reportArgumentType hits are pre-existing: LiteLLM_Params(**merged)
in _create_deployment_object already fails this check for all ~165 of its other
fields, since the merged dict's value type is partly untyped/float; adding two new
string fields to the model just grows that existing pile by two. Suppressed at the
one call site with a reason, since fixing the root typing is out of scope here.

litellm/proxy/guardrails/auto_router_compression.py

@@ -13,7 +13,7 @@ each hop sees.
 """
 
 import contextvars
-from collections.abc import Iterable, Mapping, MutableMapping, Sequence
+from collections.abc import Iterable, Mapping, Sequence
 from dataclasses import dataclass
 from types import MappingProxyType
 from typing import TYPE_CHECKING, Final
@@ -89,7 +89,7 @@ def policy_for_model(
     markers: Final = tuple(
         litellm_params
         for deployment in deployments
-        if isinstance(litellm_params := deployment.get("litellm_params"), Mapping)
+        if isinstance(litellm_params := deployment.get("litellm_params"), Mapping)  # pyright: ignore[reportUnnecessaryIsInstance]  # filters out non-Mapping
         and str(litellm_params.get("model", "")).startswith(AUTO_ROUTER_MODEL_PREFIX)
     )
     requested: Final = frozenset(request_tags)
@@ -130,7 +130,7 @@ def _active_compression_guardrails() -> tuple["CustomGuardrail", ...]:
 
 
 async def arm_pre_call(
-    data: MutableMapping[str, object],  # mutable-ok: arms the live request dict in place
+    data: dict[str, object],  # mutable-ok: arms the live request dict in place
     llm_router: "Router | None",
 ) -> None:
     """Apply an auto router's compression policy, if any, before guardrails run.
@@ -183,7 +183,11 @@ async def arm_pre_call(
 
     from litellm.litellm_core_utils.prompt_templates.factory import resolve_structured_messages
 
-    snapshot: Final = resolve_structured_messages(messages=data.get("messages"), request_kwargs=data)
+    raw_messages: Final = data.get("messages")
+    snapshot: Final = resolve_structured_messages(
+        messages=raw_messages if isinstance(raw_messages, list) else None,
+        request_kwargs=data,
+    )
     if snapshot is not None:
         _routing_messages_snapshot.set(tuple(MappingProxyType(dict(message)) for message in snapshot))
 

litellm/router.py

@@ -8644,7 +8644,7 @@ class Router:
                 raise ValueError(ptu_error)
             zeroed_pricing: Final = zeroed_ptu_pricing(_model_info, _litellm_params) if config_sourced else None
             litellm_params: Final[LiteLLM_Params] = LiteLLM_Params(
-                **(
+                **(  # pyright: ignore[reportArgumentType]  # untyped merged dict; already true for every field here
                     _litellm_params
                     if zeroed_pricing is None
                     else MappingProxyType({**_litellm_params, **zeroed_pricing})
@@ -13066,7 +13066,7 @@ class Router:
             else None
         )
 
-        pre_routing_hook_response: Final = await selected_strategy.strategy.async_pre_routing_hook(
+        routed: Final = await selected_strategy.strategy.async_pre_routing_hook(
             model=registered_model_name,
             request_kwargs=request_kwargs,
             messages=routing_messages if routing_messages is not None else messages,
@@ -13079,13 +13079,11 @@ class Router:
         # Compared by value, not identity: PreRoutingHookResponse is a pydantic model,
         # and pydantic reconstructs a validated list field rather than keeping the
         # exact object passed in, even when nothing about it changed.
-        if (
-            pre_routing_hook_response is not None
-            and routing_messages is not None
-            and pre_routing_hook_response.messages == routing_messages
-        ):
-            restored: Final = {"messages": messages}  # mutable-ok: pydantic's model_copy takes a dict
-            pre_routing_hook_response = pre_routing_hook_response.model_copy(update=restored)
+        pre_routing_hook_response: Final = (
+            routed.model_copy(update={"messages": messages})  # mutable-ok: pydantic's model_copy takes a dict
+            if routed is not None and routing_messages is not None and routed.messages == routing_messages
+            else routed
+        )
         self._record_routing_decision(
             request_kwargs=request_kwargs,
             routing_decision=(pre_routing_hook_response.routing_decision if pre_routing_hook_response else None),