fix(bedrock): forward named-function name in parallel tool_choice config

CodeRabbit follow-up: for a named-function tool_choice with
parallel_tool_calls=False, the config emitted {"type": "tool", ...} but dropped
the function name. _apply_parallel_tool_use_config then removes the native
toolChoice that carried the name, so Bedrock received a nameless "tool" choice
and rejected it.

Mirror the native Anthropic transform (which sets _tool_choice["name"] =
_tool_name): extract _bedrock_parallel_tool_choice() to build the full payload
(type + disable_parallel_tool_use, plus name when type == "tool").

Live before/after against Bedrock claude-sonnet-5 (named tool_choice +
parallel_tool_calls=False):
- before: 400 BadRequest "tool_choice.tool.name: Field required"
- after:  200, single tool_call to the named function
Added a parametrized name assertion + an end-to-end test asserting the request
carries {"type": "tool", "name": ..., "disable_parallel_tool_use": True} and
the native toolChoice is dropped. Non-vacuous (both fail against the nameless
build). ruff/lint clean, C901 strict budget unchanged.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

litellm/llms/bedrock/chat/converse_transformation.py

@@ -115,6 +115,30 @@ def _bedrock_tool_choice_type(tool_choice: Any) -> str:
     return "auto"
 
 
+def _bedrock_parallel_tool_choice(tool_choice: Any, disable_parallel: bool) -> dict:
+    """Build the Anthropic-on-Bedrock ``tool_choice`` payload for the
+    parallel-tool-use config.
+
+    Derives ``type`` from an explicit tool_choice (see
+    ``_bedrock_tool_choice_type``) and carries the ``disable_parallel_tool_use``
+    flag this config exists to set. For a named-function choice (``type ==
+    "tool"``) it also forwards the function ``name`` — mirroring the native
+    Anthropic transform (``_tool_choice["name"] = _tool_name``). Without the
+    name, ``_apply_parallel_tool_use_config`` drops the native ``toolChoice``
+    that carried it, so Bedrock would receive ``type="tool"`` with no tool named
+    and reject the request.
+    """
+    payload: dict = {
+        "type": _bedrock_tool_choice_type(tool_choice),
+        "disable_parallel_tool_use": disable_parallel,
+    }
+    if payload["type"] == "tool" and isinstance(tool_choice, dict):
+        name = tool_choice.get("function", {}).get("name")
+        if name:
+            payload["name"] = name
+    return payload
+
+
 def _apply_parallel_tool_use_config(
     parallel_tool_use_config: dict,
     additional_request_params: dict,
@@ -945,10 +969,7 @@ class AmazonConverseConfig(BaseConfig):
                 # defaults to ``type="auto"`` only when none was given). Without a
                 # ``type`` Bedrock Converse returns 400 "missing field `type`".
                 optional_params["_parallel_tool_use_config"] = {
-                    "tool_choice": {
-                        "type": _bedrock_tool_choice_type(non_default_params.get("tool_choice")),
-                        "disable_parallel_tool_use": not value,
-                    }
+                    "tool_choice": _bedrock_parallel_tool_choice(non_default_params.get("tool_choice"), not value)
                 }
             if param == "thinking":
                 optional_params["thinking"] = value

tests/test_litellm/llms/bedrock/chat/test_converse_transformation.py

@@ -696,17 +696,24 @@ def test_parallel_tool_calls_tool_choice_includes_type(model: str):
 
 
 @pytest.mark.parametrize(
-    "tool_choice, expected_type",
+    "tool_choice, expected_type, expected_name",
     [
         # An explicit tool_choice must drive the parallel-config type rather than
         # being silently overridden with "auto" (mirrors the native Anthropic
         # transform, which sets disable_parallel_tool_use on the existing choice).
-        ("required", "any"),
-        ("auto", "auto"),
-        ({"type": "function", "function": {"name": "get_current_weather"}}, "tool"),
+        ("required", "any", None),
+        ("auto", "auto", None),
+        # A named-function choice must forward the function name alongside
+        # type="tool" — else _apply_parallel_tool_use_config drops the native
+        # toolChoice carrying it and Bedrock gets a nameless "tool" choice.
+        (
+            {"type": "function", "function": {"name": "get_current_weather"}},
+            "tool",
+            "get_current_weather",
+        ),
     ],
 )
-def test_parallel_tool_calls_preserves_explicit_tool_choice_type(tool_choice, expected_type):
+def test_parallel_tool_calls_preserves_explicit_tool_choice_type(tool_choice, expected_type, expected_name):
     old_env = os.environ.get("LITELLM_LOCAL_MODEL_COST_MAP")
     old_cost = litellm.model_cost
     os.environ["LITELLM_LOCAL_MODEL_COST_MAP"] = "True"
@@ -726,6 +733,53 @@ def test_parallel_tool_calls_preserves_explicit_tool_choice_type(tool_choice, ex
         tc = optional_params["_parallel_tool_use_config"]["tool_choice"]
         assert tc["type"] == expected_type, f"expected {expected_type}, got {tc}"
         assert tc["disable_parallel_tool_use"] is True
+        assert tc.get("name") == expected_name, f"name mismatch: {tc}"
+    finally:
+        litellm.model_cost = old_cost
+        if old_env is None:
+            os.environ.pop("LITELLM_LOCAL_MODEL_COST_MAP", None)
+        else:
+            os.environ["LITELLM_LOCAL_MODEL_COST_MAP"] = old_env
+
+
+def test_parallel_tool_calls_named_function_survives_to_request():
+    """End-to-end: a named-function tool_choice with parallel_tool_calls=False
+    must reach Bedrock as a single, complete tool_choice — type="tool" WITH the
+    function name — in additionalModelRequestFields, and the native toolChoice
+    must be dropped so the two don't conflict."""
+    old_env = os.environ.get("LITELLM_LOCAL_MODEL_COST_MAP")
+    old_cost = litellm.model_cost
+    os.environ["LITELLM_LOCAL_MODEL_COST_MAP"] = "True"
+    litellm.model_cost = litellm.get_model_cost_map(url="")
+    try:
+        config = AmazonConverseConfig()
+        optional_params = config.map_openai_params(
+            model="anthropic.claude-sonnet-5",
+            non_default_params={
+                "tool_choice": {
+                    "type": "function",
+                    "function": {"name": "get_current_weather"},
+                },
+                "parallel_tool_calls": False,
+                "tools": _TOOL_PARAM,
+            },
+            optional_params={},
+            drop_params=False,
+        )
+        data = config._transform_request_helper(
+            model="anthropic.claude-sonnet-5",
+            system_content_blocks=[],
+            optional_params=optional_params,
+            messages=None,
+        )
+        tool_choice = data["additionalModelRequestFields"]["tool_choice"]
+        assert tool_choice == {
+            "type": "tool",
+            "name": "get_current_weather",
+            "disable_parallel_tool_use": True,
+        }
+        # Native toolChoice dropped to avoid the conflicting-field 400.
+        assert "toolChoice" not in data.get("toolConfig", {})
     finally:
         litellm.model_cost = old_cost
         if old_env is None: