fix(bedrock): forward freeform tools as parameterless toolSpecs, dropping the custom field

OpenAI Agents SDK freeform tools ({"type": "custom", "name": ...,
"custom": {...}}) carry a top-level name and no function payload. On
v1.90.1 the custom key reached Bedrock Converse and the request failed
with 400 "tools.0.custom.strict: Extra inputs are not permitted"
(#38799); on current main the tool is silently dropped by the
unnamed-builtin guard, so the model never sees it.

A named type=custom tool is now forwarded as a parameterless toolSpec
with the provider-specific extras stripped; nameless built-ins
(web_search, image_generation) and other named built-ins (namespace,
tool_search) are still dropped.

Fixes #38799

litellm/litellm_core_utils/prompt_templates/factory.py

@@ -5064,14 +5064,29 @@ def _bedrock_tools_pt(tools: list, model: str | None = None) -> list[BedrockTool
             tool_block_list.append(tool)
             continue
 
-        # Responses built-in tools (web_search, image_generation, namespace, tool_search,
-        # custom) carry neither an OpenAI "function" nor an Anthropic "input_schema" and have
-        # no Bedrock toolSpec equivalent; drop them instead of emitting an empty junk toolSpec.
-        if isinstance(tool, dict) and "function" not in tool and "input_schema" not in tool:
+        # OpenAI Agents SDK freeform tools ({"type": "custom", "name": ...,
+        # "description": ..., "custom": {...}}) carry a top-level name and no
+        # function payload; forward them as parameterless toolSpecs, dropping
+        # provider-specific extras like `custom`, which Bedrock rejects (#38799).
+        # Other named-but-builtin tools (e.g. namespace) and nameless Responses
+        # built-ins (web_search, image_generation, ...) have no Bedrock toolSpec
+        # equivalent and are still dropped below.
+        if (
+            isinstance(tool, dict)
+            and "function" not in tool
+            and "input_schema" not in tool
+            and tool.get("type") == "custom"
+        ):
+            freeform_name = tool.get("name")
+            if not (isinstance(freeform_name, str) and freeform_name.strip()):
+                continue
+            parameters = {"type": "object", "properties": {}}
+            raw_name = freeform_name
+            _tool_description = tool.get("description", None)
+        elif isinstance(tool, dict) and "function" not in tool and "input_schema" not in tool:
             continue
-
         # OpenAI function tools, or Anthropic Messages / Claude Code ({name, input_schema, type, ...})
-        if isinstance(tool, dict) and "input_schema" in tool and "function" not in tool:
+        elif isinstance(tool, dict) and "input_schema" in tool and "function" not in tool:
             parameters = copy.deepcopy(tool.get("input_schema") or {"type": "object", "properties": {}})
             raw_name = tool.get("name", "") or ""
             _tool_description = tool.get("description", None)

tests/test_litellm/litellm_core_utils/prompt_templates/test_litellm_core_utils_prompt_templates_factory.py

@@ -1030,6 +1030,42 @@ def test_bedrock_tools_pt_strict_parameter():
     assert "additionalProperties" not in result[0]["toolSpec"]["inputSchema"]["json"]
 
 
+def test_bedrock_tools_pt_forwards_freeform_tool_without_custom_field():
+    """OpenAI Agents SDK freeform tools carry a top-level name and a provider-specific
+    `custom` dict instead of a function payload. Bedrock rejects the `custom` key
+    outright (400 "tools.0.custom.strict: Extra inputs are not permitted"), so the
+    tool must be forwarded as a parameterless toolSpec with the extras stripped
+    rather than dropped or passed through.
+    """
+    tools = [
+        {
+            "type": "custom",
+            "name": "apply_patch",
+            "description": "Apply a unified diff patch to the workspace.",
+            "custom": {"strict": None},
+        }
+    ]
+    result = _bedrock_tools_pt(tools, model="us.anthropic.claude-sonnet-5")
+    assert len(result) == 1, "the freeform tool must not be dropped"
+    tool_spec = result[0]["toolSpec"]
+    assert tool_spec["name"] == "apply_patch"
+    assert tool_spec["description"] == "Apply a unified diff patch to the workspace."
+    assert tool_spec["inputSchema"]["json"] == {"type": "object", "properties": {}, "required": []}
+    assert "custom" not in tool_spec
+    assert "strict" not in tool_spec
+
+
+def test_bedrock_tools_pt_still_drops_unnamed_builtin_tools():
+    """Responses built-in tools (web_search, image_generation, ...) have no top-level
+    name and no Bedrock toolSpec equivalent; they must stay dropped.
+    """
+    tools = [
+        {"type": "web_search_preview"},
+        {"type": "image_generation"},
+    ]
+    assert _bedrock_tools_pt(tools, model="us.anthropic.claude-sonnet-5") == []
+
+
 def test_bedrock_image_processor_content_type_fallback_url_extension():
     """
     Test that _post_call_image_processing falls back to URL extension
@@ -1632,9 +1668,13 @@ def test_bedrock_tools_pt_does_not_handle_system_tool():
 def test_bedrock_tools_pt_drops_unmappable_responses_builtin_tools():
     """
     Regression for LIT-3858: Responses built-in tools (image_generation, namespace,
-    tool_search, custom) have no Bedrock toolSpec equivalent. They must be dropped, not
+    tool_search) have no Bedrock toolSpec equivalent. They must be dropped, not
     emitted as junk ``litellm_unnamed_tool_N`` toolSpecs the model can hallucinate calls to.
     Mappable ``function`` and Anthropic ``input_schema`` tools must survive untouched.
+
+    Named ``custom`` tools (freeform tools, e.g. the OpenAI Agents SDK's apply_patch)
+    ARE mappable — a parameterless toolSpec — and are forwarded since #38799; only
+    nameless built-ins stay dropped.
     """
     from litellm.litellm_core_utils.prompt_templates.factory import _bedrock_tools_pt
 
@@ -1657,7 +1697,7 @@ def test_bedrock_tools_pt_drops_unmappable_responses_builtin_tools():
     )
 
     names = [block["toolSpec"]["name"] for block in result if "toolSpec" in block]
-    assert names == ["noop"]
+    assert names == ["noop", "free_form"], "named built-ins like namespace must stay dropped"
     assert not any(name.startswith("litellm_unnamed_tool_") for name in names)