fix: recover from empty tool call names (#4008)

* fix: recover from empty tool call names

* test: harden empty tool call recovery

---------

Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

backend/AGENTS.md

@@ -224,7 +224,7 @@ Lead-agent middlewares are assembled in strict order across three functions: the
 4. **ThreadDataMiddleware** - Creates per-thread directories under the user's isolation scope (`backend/.deer-flow/users/{user_id}/threads/{thread_id}/user-data/{workspace,uploads,outputs}`); resolves `user_id` via `get_effective_user_id()` (falls back to `"default"` in no-auth mode)
 5. **UploadsMiddleware** - Tracks and injects newly uploaded files into conversation (lead agent only)
 6. **SandboxMiddleware** - Acquires sandbox, stores `sandbox_id` in state
-7. **DanglingToolCallMiddleware** - Injects placeholder ToolMessages for AIMessage tool_calls that lack responses (e.g., user interruption), preserving raw provider tool-call payloads in `additional_kwargs["tool_calls"]`
+7. **DanglingToolCallMiddleware** - Injects placeholder ToolMessages for AIMessage tool_calls that lack responses (e.g., user interruption), preserving raw provider tool-call payloads in `additional_kwargs["tool_calls"]`; malformed empty tool-call names are normalized to a recoverable error so strict OpenAI-compatible providers do not reject the next request
 8. **LLMErrorHandlingMiddleware** - Normalizes provider/model invocation failures into recoverable assistant-facing errors before later stages run
 9. **GuardrailMiddleware** - *(optional, if `guardrails.enabled`)* Pre-tool-call authorization via pluggable `GuardrailProvider`; returns an error ToolMessage on deny. Providers: built-in `AllowlistProvider` (zero deps), OAP policy providers (e.g. `aport-agent-guardrails`), or custom. See [docs/GUARDRAILS.md](docs/GUARDRAILS.md)
 10. **SandboxAuditMiddleware** - Audits sandboxed shell/file operations for security logging before tool execution

backend/packages/harness/deerflow/agents/middlewares/dangling_tool_call_middleware.py

@@ -30,6 +30,20 @@ logger = logging.getLogger(__name__)
 # payloads in invalid tool-call args. Keep recovery error details short so the
 # synthetic ToolMessage does not echo large or malformed content back to the model.
 _MAX_RECOVERY_ERROR_DETAIL_LEN = 500
+_UNKNOWN_TOOL_NAME = "unknown_tool"
+_EMPTY_TOOL_NAME_ERROR = "Tool call could not be executed because its name was missing or empty."
+
+
+def _valid_tool_name(name: object) -> bool:
+    return isinstance(name, str) and bool(name.strip())
+
+
+def _normalize_tool_name(name: object) -> str:
+    return name.strip() if _valid_tool_name(name) else _UNKNOWN_TOOL_NAME
+
+
+def _has_invalid_tool_name(name: object) -> bool:
+    return not _valid_tool_name(name)
 
 
 class DanglingToolCallMiddleware(AgentMiddleware[AgentState]):
@@ -54,7 +68,16 @@ class DanglingToolCallMiddleware(AgentMiddleware[AgentState]):
         normalized: list[dict] = []
 
         tool_calls = getattr(msg, "tool_calls", None) or []
-        normalized.extend(list(tool_calls))
+        for tool_call in tool_calls:
+            if not isinstance(tool_call, dict):
+                logger.debug("Skipping malformed non-dict tool_call in AIMessage: %r", tool_call)
+                continue
+            original_name = tool_call.get("name")
+            normalized_call = dict(tool_call)
+            normalized_call["name"] = _normalize_tool_name(original_name)
+            if _has_invalid_tool_name(original_name):
+                normalized_call["invalid_tool_name"] = True
+            normalized.append(normalized_call)
 
         raw_tool_calls = (getattr(msg, "additional_kwargs", None) or {}).get("tool_calls") or []
         if not tool_calls:
@@ -77,31 +100,36 @@ class DanglingToolCallMiddleware(AgentMiddleware[AgentState]):
                             parsed_args = {}
                         args = parsed_args if isinstance(parsed_args, dict) else {}
 
-                normalized.append(
-                    {
-                        "id": raw_tc.get("id"),
-                        "name": name or "unknown",
-                        "args": args if isinstance(args, dict) else {},
-                    }
-                )
+                normalized_call = {
+                    "id": raw_tc.get("id"),
+                    "name": _normalize_tool_name(name),
+                    "args": args if isinstance(args, dict) else {},
+                }
+                if _has_invalid_tool_name(name):
+                    normalized_call["invalid_tool_name"] = True
+                normalized.append(normalized_call)
 
         for invalid_tc in getattr(msg, "invalid_tool_calls", None) or []:
             if not isinstance(invalid_tc, dict):
                 continue
-            normalized.append(
-                {
-                    "id": invalid_tc.get("id"),
-                    "name": invalid_tc.get("name") or "unknown",
-                    "args": {},
-                    "invalid": True,
-                    "error": invalid_tc.get("error"),
-                }
-            )
+            original_name = invalid_tc.get("name")
+            normalized_call = {
+                "id": invalid_tc.get("id"),
+                "name": _normalize_tool_name(original_name),
+                "args": {},
+                "invalid": True,
+                "error": invalid_tc.get("error"),
+            }
+            if _has_invalid_tool_name(original_name):
+                normalized_call["invalid_tool_name"] = True
+            normalized.append(normalized_call)
 
         return normalized
 
     @staticmethod
     def _synthetic_tool_message_content(tool_call: dict) -> str:
+        if tool_call.get("invalid_tool_name"):
+            return f"[{_EMPTY_TOOL_NAME_ERROR} Use one of the available tool names when retrying.]"
         if tool_call.get("invalid"):
             name = tool_call.get("name")
             error = tool_call.get("error")
@@ -125,6 +153,69 @@ class DanglingToolCallMiddleware(AgentMiddleware[AgentState]):
             return "[Tool call could not be executed because its arguments were invalid.]"
         return "[Tool call was interrupted and did not return a result.]"
 
+    @staticmethod
+    def _sanitize_ai_message_tool_names(msg):
+        """Return an AIMessage with model-bound tool-call names made non-empty."""
+        if getattr(msg, "type", None) != "ai":
+            return msg
+
+        changed = False
+        update: dict = {}
+
+        tool_calls = getattr(msg, "tool_calls", None)
+        if tool_calls:
+            structured_changed = False
+            sanitized_tool_calls = []
+            for tool_call in tool_calls:
+                if not isinstance(tool_call, dict):
+                    sanitized_tool_calls.append(tool_call)
+                    continue
+                name = tool_call.get("name")
+                sanitized = dict(tool_call)
+                normalized_name = _normalize_tool_name(name)
+                if sanitized.get("name") != normalized_name:
+                    sanitized["name"] = normalized_name
+                    structured_changed = True
+                sanitized_tool_calls.append(sanitized)
+            if structured_changed:
+                update["tool_calls"] = sanitized_tool_calls
+                changed = True
+
+        additional_kwargs = dict(getattr(msg, "additional_kwargs", {}) or {})
+        raw_tool_calls = additional_kwargs.get("tool_calls")
+        if isinstance(raw_tool_calls, list):
+            raw_changed = False
+            sanitized_raw_tool_calls = []
+            for raw_tool_call in raw_tool_calls:
+                if not isinstance(raw_tool_call, dict):
+                    sanitized_raw_tool_calls.append(raw_tool_call)
+                    continue
+
+                sanitized_raw = dict(raw_tool_call)
+                function = sanitized_raw.get("function")
+                if isinstance(function, dict):
+                    sanitized_function = dict(function)
+                    normalized_name = _normalize_tool_name(sanitized_function.get("name"))
+                    if sanitized_function.get("name") != normalized_name:
+                        sanitized_function["name"] = normalized_name
+                        sanitized_raw["function"] = sanitized_function
+                        raw_changed = True
+                else:
+                    normalized_name = _normalize_tool_name(sanitized_raw.get("name"))
+                    if sanitized_raw.get("name") != normalized_name:
+                        sanitized_raw["name"] = normalized_name
+                        raw_changed = True
+                sanitized_raw_tool_calls.append(sanitized_raw)
+
+            if raw_changed:
+                additional_kwargs["tool_calls"] = sanitized_raw_tool_calls
+                update["additional_kwargs"] = additional_kwargs
+                changed = True
+
+        if not changed:
+            return msg
+        return msg.model_copy(update=update)
+
     def _build_patched_messages(self, messages: list) -> list | None:
         """Return messages with tool results grouped after their tool-call AIMessage.
 
@@ -151,10 +242,13 @@ class DanglingToolCallMiddleware(AgentMiddleware[AgentState]):
             if isinstance(msg, ToolMessage) and msg.tool_call_id in tool_call_ids:
                 continue
 
-            patched.append(msg)
+            sanitized_msg = self._sanitize_ai_message_tool_names(msg)
+            patched.append(sanitized_msg)
             if getattr(msg, "type", None) != "ai":
                 continue
 
+            # Intentionally inspect the original message so empty names can be
+            # classified before the sanitized message replaces them.
             for tc in self._message_tool_calls(msg):
                 tc_id = tc.get("id")
                 if not tc_id:
@@ -163,6 +257,8 @@ class DanglingToolCallMiddleware(AgentMiddleware[AgentState]):
                 tool_msg_queue = tool_messages_by_id.get(tc_id)
                 existing_tool_msg = tool_msg_queue.popleft() if tool_msg_queue else None
                 if existing_tool_msg is not None:
+                    if tc.get("invalid_tool_name") and _has_invalid_tool_name(existing_tool_msg.name):
+                        existing_tool_msg = existing_tool_msg.model_copy(update={"name": tc["name"]})
                     patched.append(existing_tool_msg)
                 else:
                     patched.append(

backend/tests/test_dangling_tool_call_middleware.py

@@ -5,6 +5,10 @@ from unittest.mock import AsyncMock, MagicMock
 import pytest
 from langchain_core.messages import AIMessage, HumanMessage, ToolMessage
 
+# Intentional private import: these tests lock the OpenAI serialization boundary
+# that strict providers reject when assistant tool-call names are empty.
+from langchain_openai.chat_models.base import _convert_message_to_dict
+
 from deerflow.agents.middlewares.dangling_tool_call_middleware import (
     DanglingToolCallMiddleware,
 )
@@ -59,6 +63,27 @@ class TestBuildPatchedMessagesNoPatch:
         ]
         assert mw._build_patched_messages(msgs) is None
 
+    def test_valid_tool_call_names_are_sanitization_noop(self):
+        mw = DanglingToolCallMiddleware()
+        msgs = [
+            AIMessage(
+                content="",
+                tool_calls=[_tc("bash", "call_1")],
+                additional_kwargs={
+                    "tool_calls": [
+                        {
+                            "id": "call_1",
+                            "type": "function",
+                            "function": {"name": "bash", "arguments": "{}"},
+                        }
+                    ]
+                },
+            ),
+            _tool_msg("call_1", "bash"),
+        ]
+
+        assert mw._build_patched_messages(msgs) is None
+
 
 class TestBuildPatchedMessagesPatching:
     def test_single_dangling_call(self):
@@ -158,6 +183,142 @@ class TestBuildPatchedMessagesPatching:
         assert patched[1].name == "bash"
         assert patched[1].status == "error"
 
+    def test_empty_structured_tool_call_name_is_sanitized(self):
+        mw = DanglingToolCallMiddleware()
+        msgs = [_ai_with_tool_calls([_tc("", "empty_name_call")])]
+
+        patched = mw._build_patched_messages(msgs)
+
+        assert patched is not None
+        assert patched[0].tool_calls[0]["name"] == "unknown_tool"
+        payload = _convert_message_to_dict(patched[0])
+        assert payload["tool_calls"][0]["function"]["name"] == "unknown_tool"
+        assert isinstance(patched[1], ToolMessage)
+        assert patched[1].tool_call_id == "empty_name_call"
+        assert patched[1].name == "unknown_tool"
+        assert patched[1].status == "error"
+        assert "name was missing or empty" in patched[1].content
+
+    @pytest.mark.parametrize(
+        "raw_tool_call",
+        [
+            {"id": "missing_name_call", "type": "function", "function": {"arguments": "{}"}},
+            {"id": "non_string_name_call", "type": "function", "function": {"name": 42, "arguments": "{}"}},
+        ],
+    )
+    def test_malformed_raw_provider_tool_call_name_is_sanitized(self, raw_tool_call):
+        mw = DanglingToolCallMiddleware()
+        msgs = [
+            AIMessage.model_construct(
+                content="",
+                type="ai",
+                tool_calls=[],
+                invalid_tool_calls=[],
+                additional_kwargs={"tool_calls": [raw_tool_call]},
+                response_metadata={},
+            )
+        ]
+
+        patched = mw._build_patched_messages(msgs)
+
+        assert patched is not None
+        assert patched[0].additional_kwargs["tool_calls"][0]["function"]["name"] == "unknown_tool"
+        payload = _convert_message_to_dict(patched[0])
+        assert payload["tool_calls"][0]["function"]["name"] == "unknown_tool"
+        assert patched[1].name == "unknown_tool"
+        assert patched[1].status == "error"
+
+    def test_existing_tool_result_still_sanitizes_empty_structured_tool_call_name(self):
+        mw = DanglingToolCallMiddleware()
+        msgs = [
+            _ai_with_tool_calls([_tc(" ", "empty_name_call")]),
+            ToolMessage(content="Error: invalid tool", tool_call_id="empty_name_call", name=""),
+        ]
+
+        patched = mw._build_patched_messages(msgs)
+
+        assert patched is not None
+        assert patched[0].tool_calls[0]["name"] == "unknown_tool"
+        payload = _convert_message_to_dict(patched[0])
+        assert payload["tool_calls"][0]["function"]["name"] == "unknown_tool"
+        assert patched[1].tool_call_id == "empty_name_call"
+        assert patched[1].name == "unknown_tool"
+
+    def test_raw_provider_tool_call_empty_function_name_is_sanitized(self):
+        mw = DanglingToolCallMiddleware()
+        msgs = [
+            AIMessage(
+                content="",
+                tool_calls=[],
+                additional_kwargs={
+                    "tool_calls": [
+                        {
+                            "id": "raw_empty_name_call",
+                            "type": "function",
+                            "function": {"name": "", "arguments": "{}"},
+                        }
+                    ]
+                },
+            )
+        ]
+
+        patched = mw._build_patched_messages(msgs)
+
+        assert patched is not None
+        raw_tool_call = patched[0].additional_kwargs["tool_calls"][0]
+        assert raw_tool_call["function"]["name"] == "unknown_tool"
+        payload = _convert_message_to_dict(patched[0])
+        assert payload["tool_calls"][0]["function"]["name"] == "unknown_tool"
+        assert patched[1].tool_call_id == "raw_empty_name_call"
+        assert patched[1].name == "unknown_tool"
+        assert patched[1].status == "error"
+        assert "name was missing or empty" in patched[1].content
+
+    def test_valid_structured_call_with_empty_raw_provider_name_is_sanitized(self):
+        mw = DanglingToolCallMiddleware()
+        msgs = [
+            AIMessage.model_construct(
+                content="",
+                type="ai",
+                tool_calls=[_tc("bash", "call_1")],
+                invalid_tool_calls=[],
+                additional_kwargs={
+                    "tool_calls": [
+                        {
+                            "id": "call_1",
+                            "type": "function",
+                            "function": {"name": "", "arguments": "{}"},
+                        }
+                    ]
+                },
+                response_metadata={},
+            ),
+            _tool_msg("call_1", "bash"),
+        ]
+
+        patched = mw._build_patched_messages(msgs)
+
+        assert patched is not None
+        assert patched[0].tool_calls[0]["name"] == "bash"
+        raw_tool_call = patched[0].additional_kwargs["tool_calls"][0]
+        assert raw_tool_call["function"]["name"] == "unknown_tool"
+        payload = _convert_message_to_dict(patched[0])
+        assert payload["tool_calls"][0]["function"]["name"] == "bash"
+        assert patched[1].tool_call_id == "call_1"
+        assert patched[1].name == "bash"
+
+    def test_empty_name_invalid_tool_call_uses_name_recovery_message(self):
+        mw = DanglingToolCallMiddleware()
+        msgs = [_ai_with_invalid_tool_calls([_invalid_tc(name="", tc_id="empty_invalid_call")])]
+
+        patched = mw._build_patched_messages(msgs)
+
+        assert patched is not None
+        assert patched[1].tool_call_id == "empty_invalid_call"
+        assert patched[1].name == "unknown_tool"
+        assert "name was missing or empty" in patched[1].content
+        assert "arguments were invalid" not in patched[1].content
+
     def test_non_adjacent_tool_result_is_moved_next_to_tool_call(self):
         middleware = DanglingToolCallMiddleware()
         msgs = [