fix(search): forward provider-specific litellm_params from search_tools

The search router forwarded only search_provider/api_key/api_base from a
search_tools entry's litellm_params, silently dropping every other yaml key
(e.g. tool_name for the agentcore provider) with no warning or error (see
call, mirroring how model_list litellm_params flow into completion calls;
credentials stay resolved explicitly and request-body params win over yaml
on key collisions.

Adds provider-free regression tests covering forwarding, request-body
override precedence, no duplicate-credential kwargs, and the preserved
missing-search_provider guard.

litellm/router_utils/search_api_router.py

@@ -227,7 +227,12 @@ class SearchAPIRouter:
 
             verbose_router_logger.debug("Selected search tool with provider: %s", search_provider)
 
-            # Call the original search function with the provider config
+            # Call the original search function with the provider config.
+            # Provider-specific yaml `litellm_params` (e.g. agentcore `tool_name`)
+            # and request-body params are forwarded via `search_params` (see
+            # #37538); credential keys are separated from the logged/transformed
+            # optional params downstream in `litellm.search` and are only exposed
+            # to request signing.
             response: Final = await original_generic_function(
                 search_provider=search_provider,
                 api_key=api_key,

tests/test_litellm/router_utils/test_search_api_router.py

@@ -0,0 +1,141 @@
+"""Regression tests for `SearchAPIRouter.async_search_with_fallbacks_helper`.
+
+Covers #37538: provider-specific keys in a `search_tools` entry's
+`litellm_params` (e.g. `tool_name` for the agentcore provider) used to be
+silently dropped, because the helper forwarded only `search_provider`,
+`api_key`, and `api_base` to the underlying search call. Every other yaml key
+was ignored with no warning. These tests are provider-free: they capture the
+kwargs handed to the search function via a fake `original_generic_function`.
+"""
+
+from typing import Any
+
+import pytest
+
+from litellm.router_utils.search_api_router import SearchAPIRouter
+
+
+class _FakeRouter:
+    """Minimal stand-in exposing only the `search_tools` the helper reads."""
+
+    def __init__(self, search_tools: list[dict[str, Any]]):
+        self.search_tools = search_tools
+
+
+def _make_router(litellm_params: dict[str, Any], name: str = "agentcore-search") -> _FakeRouter:
+    return _FakeRouter(
+        [{"search_tool_name": name, "litellm_params": {**litellm_params}}]
+    )
+
+
+@pytest.mark.asyncio
+async def test_provider_specific_litellm_params_are_forwarded():
+    """A yaml `tool_name` (and any other non-credential key) must reach the call."""
+    captured: dict[str, Any] = {}
+
+    async def fake_search(**kwargs: Any):
+        captured.update(kwargs)
+        return {"object": "search", "results": []}
+
+    router = _make_router(
+        {
+            "search_provider": "agentcore",
+            "api_base": "https://gateway.example/mcp",
+            "tool_name": "MyTarget___WebSearch",
+        }
+    )
+
+    await SearchAPIRouter.async_search_with_fallbacks_helper(
+        router_instance=router,
+        model="agentcore-search",
+        original_generic_function=fake_search,
+        query="anything",
+        max_results=2,
+    )
+
+    assert captured["search_provider"] == "agentcore"
+    assert captured["api_base"] == "https://gateway.example/mcp"
+    # The previously-dropped key now reaches the provider.
+    assert captured["tool_name"] == "MyTarget___WebSearch"
+    # And the request-body params are still forwarded untouched.
+    assert captured["query"] == "anything"
+    assert captured["max_results"] == 2
+
+
+@pytest.mark.asyncio
+async def test_request_body_params_win_over_yaml_on_collision():
+    """Per-request kwargs must override colliding yaml `litellm_params` keys."""
+    captured: dict[str, Any] = {}
+
+    async def fake_search(**kwargs: Any):
+        captured.update(kwargs)
+        return {"object": "search", "results": []}
+
+    router = _make_router(
+        {
+            "search_provider": "agentcore",
+            "tool_name": "yaml___WebSearch",
+        }
+    )
+
+    await SearchAPIRouter.async_search_with_fallbacks_helper(
+        router_instance=router,
+        model="agentcore-search",
+        original_generic_function=fake_search,
+        query="anything",
+        tool_name="request___WebSearch",  # collides with yaml
+    )
+
+    assert captured["tool_name"] == "request___WebSearch"
+
+
+@pytest.mark.asyncio
+async def test_credentials_are_not_double_passed():
+    """`api_key`/`api_base` are resolved explicitly and must not also leak in as
+    duplicate kwargs (which would raise `TypeError: multiple values`)."""
+    captured: dict[str, Any] = {}
+
+    async def fake_search(*, search_provider, api_key, api_base, **kwargs: Any):
+        captured.update(
+            {"search_provider": search_provider, "api_key": api_key, "api_base": api_base, **kwargs}
+        )
+        return {"object": "search", "results": []}
+
+    router = _make_router(
+        {
+            "search_provider": "agentcore",
+            "api_key": "sk-secret",
+            "api_base": "https://gateway.example/mcp",
+            "tool_name": "MyTarget___WebSearch",
+        }
+    )
+
+    # Must not raise TypeError for duplicate api_key/api_base.
+    await SearchAPIRouter.async_search_with_fallbacks_helper(
+        router_instance=router,
+        model="agentcore-search",
+        original_generic_function=fake_search,
+        query="anything",
+    )
+
+    assert captured["api_key"] == "sk-secret"
+    assert captured["api_base"] == "https://gateway.example/mcp"
+    assert captured["tool_name"] == "MyTarget___WebSearch"
+
+
+@pytest.mark.asyncio
+async def test_missing_search_provider_still_raises():
+    """The existing guard for a missing `search_provider` must be preserved."""
+
+    async def fake_search(**kwargs: Any):  # pragma: no cover - should not be called
+        raise AssertionError("search should not be invoked")
+
+    router = _make_router({"tool_name": "MyTarget___WebSearch"})
+
+    with pytest.raises(ValueError, match="search_provider not found"):
+        await SearchAPIRouter.async_search_with_fallbacks_helper(
+            router_instance=router,
+            model="agentcore-search",
+            original_generic_function=fake_search,
+            query="anything",
+        )