fix(responses): detect emulated file search from context, not a tool name

A client function named litellm_file_search turned the tool_search lowering off even when no file search was emulated. Emulated file_search now marks its nested calls in the internal request context, next to is_internal_call, and the lowering only steps aside during that phase

litellm/_internal_context.py

@@ -24,6 +24,23 @@ _billing_time: Final[ContextVar[datetime | None]] = ContextVar("billing_time", d
 _post_response: Final[ContextVar[bool]] = ContextVar("post_response", default=False)
 
 
+_emulated_file_search: Final[ContextVar[bool]] = ContextVar("emulated_file_search", default=False)
+
+
+@contextmanager
+def emulated_file_search_phase() -> Generator[None]:
+    """Nested calls of emulated file_search, whose answer keeps only its own tool calls."""
+    token: Final = _emulated_file_search.set(True)
+    try:
+        yield
+    finally:
+        _emulated_file_search.reset(token)
+
+
+def in_emulated_file_search() -> bool:
+    return _emulated_file_search.get()
+
+
 @contextmanager
 def post_response_phase() -> Generator[None]:
     """Work the caller no longer waits for (success callbacks, response-cache writes), including tasks it spawns."""

litellm/responses/file_search/emulated_handler.py

@@ -19,7 +19,7 @@ from typing import TYPE_CHECKING, Any, Final, TypeAlias, cast  # noqa: TID251  #
 
 from typing_extensions import NotRequired, ReadOnly, TypedDict
 
-from litellm._internal_context import is_internal_call
+from litellm._internal_context import emulated_file_search_phase, is_internal_call
 from litellm._logging import verbose_logger
 from litellm.types.llms.openai import ResponseOutputItem, ResponsesAPIResponse
 from litellm.types.vector_stores import VectorStoreSearchResult
@@ -537,15 +537,16 @@ async def aresponses_with_emulated_file_search(
     _prev_internal: Final = is_internal_call.get()
     is_internal_call.set(True)
     try:
-        first_response: Final[ResponsesAPIResponse] = cast(
-            ResponsesAPIResponse,
-            await _call_aresponses(
-                input=input,
-                model=model,
-                tools=transformed_tools or None,
-                **call_kwargs,
-            ),
-        )
+        with emulated_file_search_phase():
+            first_response: Final[ResponsesAPIResponse] = cast(
+                ResponsesAPIResponse,
+                await _call_aresponses(
+                    input=input,
+                    model=model,
+                    tools=transformed_tools or None,
+                    **call_kwargs,
+                ),
+            )
     finally:
         is_internal_call.set(_prev_internal)
 
@@ -601,15 +602,16 @@ async def aresponses_with_emulated_file_search(
     # Also an internal sub-call; billing is suppressed so the outer call fires once.
     is_internal_call.set(True)
     try:
-        final_response: Final[ResponsesAPIResponse] = cast(
-            ResponsesAPIResponse,
-            await _call_aresponses(
-                input=follow_up_input,
-                model=model,
-                tools=None,  # no tools needed for the answer step
-                **call_kwargs,
-            ),
-        )
+        with emulated_file_search_phase():
+            final_response: Final[ResponsesAPIResponse] = cast(
+                ResponsesAPIResponse,
+                await _call_aresponses(
+                    input=follow_up_input,
+                    model=model,
+                    tools=None,  # no tools needed for the answer step
+                    **call_kwargs,
+                ),
+            )
     finally:
         is_internal_call.set(_prev_internal)
 

litellm/responses/main.py

@@ -13,6 +13,7 @@ from pydantic import BaseModel, TypeAdapter, ValidationError
 from typing_extensions import assert_never
 
 import litellm
+from litellm._internal_context import in_emulated_file_search
 from litellm._logging import verbose_logger
 from litellm.completion_extras.litellm_responses_transformation.transformation import (
     LiteLLMResponsesTransformationHandler,
@@ -34,7 +35,7 @@ from litellm.responses.litellm_completion_transformation.handler import (
     LiteLLMCompletionTransformationHandler,
 )
 from litellm.responses.mcp.request_context import MCPRequestContext
-from litellm.responses.tool_search.lowering import declares_function, needs_tool_search_lowering
+from litellm.responses.tool_search.lowering import needs_tool_search_lowering
 from litellm.responses.utils import ResponsesAPIRequestUtils
 from litellm.types.llms.openai import (
     PromptObject,
@@ -1147,13 +1148,6 @@ def _supports_tool_search_natively(responses_api_provider_config: BaseResponsesA
     return declared
 
 
-def _emulates_file_search(tools: Sequence[object] | None) -> bool:
-    # emulated file_search answers with its own calls only, so it would drop a lowered tool_search call
-    from litellm.responses.file_search.emulated_handler import FILE_SEARCH_FUNCTION_NAME
-
-    return declares_function(tools, FILE_SEARCH_FUNCTION_NAME)
-
-
 def _responses_try_dispatch_lowered_tool_search(
     *,
     tools: Iterable[ToolParam] | None,
@@ -1180,7 +1174,7 @@ def _responses_try_dispatch_lowered_tool_search(
         or _bridges_to_chat_completions(responses_api_provider_config, use_chat_completions_api)
         or _supports_tool_search_natively(responses_api_provider_config, model_info)
         or not needs_tool_search_lowering(input, declared_tools)
-        or _emulates_file_search(declared_tools)
+        or in_emulated_file_search()
     ):
         return None
     from litellm.responses.tool_search.handler import (

litellm/responses/tool_search/lowering.py

@@ -217,7 +217,7 @@ def _lowered_tool_choice(tool_choice: ToolChoice | None) -> ToolChoice | None:
     return {"type": "function", "name": TOOL_SEARCH_FUNCTION_NAME}
 
 
-def declares_function(tools: Sequence[object] | None, name: str) -> bool:
+def _declares_function(tools: Sequence[object] | None, name: str) -> bool:
     return ("function", name) in (_merge_key(index, tool) for index, tool in enumerate(tools or ()))
 
 
@@ -227,7 +227,7 @@ def lower_tool_search_request(
     tool_choice: ToolChoice | None,
 ) -> ToolSearchLowering:
     declared: Final = tuple(tools or ())
-    if _declares_client_tool_search(declared) and declares_function(declared, TOOL_SEARCH_FUNCTION_NAME):
+    if _declares_client_tool_search(declared) and _declares_function(declared, TOOL_SEARCH_FUNCTION_NAME):
         return ToolSearchFunctionNameTaken()
     items: Final = () if isinstance(input, str) else tuple(input)
     lowered_tools: Final = _merged_tools((*(_lowered_tool(tool) for tool in declared), *_loaded_tools(items)))

tests/unit/responses/tool_search/test_handler.py

@@ -200,6 +200,20 @@ async def test_emulated_file_search_leaves_client_tool_search_as_declared():
     assert _types(upstream.bodies[0]["tools"]) == ["tool_search", "function"]
 
 
+@pytest.mark.asyncio
+async def test_a_client_function_named_like_the_file_search_emulation_keeps_tool_search_lowered():
+    upstream: Final = _Upstream()
+    own_function: Final = {
+        "type": "function",
+        "name": "litellm_file_search",
+        "parameters": {"type": "object", "properties": {}},
+    }
+
+    await _hosted_vllm_call(upstream, tools=[CLIENT_TOOL_SEARCH, own_function])
+
+    assert [tool["name"] for tool in upstream.bodies[0]["tools"]] == ["tool_search", "litellm_file_search"]
+
+
 @pytest.mark.asyncio
 async def test_the_call_is_logged_once_with_the_tool_search_call(monkeypatch: pytest.MonkeyPatch):
     success_log: Final = _SuccessLog("tool-search-logged-once")