fix(proxy): build failure headers immutably to keep LIT002 within budget

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

litellm/proxy/batches_endpoints/endpoints.py

@@ -7,6 +7,7 @@
 import asyncio
 import os
 from collections.abc import Mapping
+from types import MappingProxyType
 from typing import Any, Final, cast
 
 from fastapi import APIRouter, Depends, HTTPException, Path, Request, Response
@@ -731,7 +732,7 @@ async def list_batches(
     )
 
     verbose_proxy_logger.debug("GET /v1/batches after=%s limit=%s", after, limit)
-    data: dict = {}
+    data: Mapping[str, object] = MappingProxyType({})
     try:
         if llm_router is None:
             raise HTTPException(

litellm/proxy/common_utils/openai_error_payload.py

@@ -68,3 +68,10 @@ def with_litellm_call_id(exc: ProxyException, litellm_call_id: str | None) -> Pr
     if litellm_call_id is not None:
         exc.headers.setdefault(LITELLM_CALL_ID_HEADER, litellm_call_id)
     return exc
+
+
+def headers_with_litellm_call_id(headers: Mapping[str, str] | None, litellm_call_id: str) -> Mapping[str, str]:
+    """``headers`` plus ``x-litellm-call-id``, keeping the value they already carry under that name."""
+    if headers is None:
+        return MappingProxyType({LITELLM_CALL_ID_HEADER: litellm_call_id})
+    return MappingProxyType({LITELLM_CALL_ID_HEADER: litellm_call_id, **headers})

litellm/proxy/proxy_server.py

@@ -392,7 +392,7 @@ from litellm.proxy.common_utils.openai_endpoint_utils import (
     remove_sensitive_info_from_deployment,
 )
 from litellm.proxy.common_utils.openai_error_payload import (
-    LITELLM_CALL_ID_HEADER,
+    headers_with_litellm_call_id,
     litellm_call_id_headers,
     with_litellm_call_id,
 )
@@ -11696,7 +11696,7 @@ async def audio_speech(
             raise HTTPException(
                 status_code=e.status_code,
                 detail=e.detail,
-                headers={LITELLM_CALL_ID_HEADER: litellm_call_id, **(e.headers or {})},
+                headers=headers_with_litellm_call_id(e.headers, litellm_call_id),
             )
         raise ProxyException(
             message=getattr(e, "message", f"{e}"),