fix(middleware): degrade tool-call exceptions to error tool messages (#1110)

* fix(middleware): degrade tool-call exceptions to error tool messages

* update script

* fix(middleware): preserve LangGraph control-flow exceptions in tool error handling

backend/tests/test_tool_error_handling_middleware.py

@@ -0,0 +1,96 @@
+from types import SimpleNamespace
+
+import pytest
+from langchain_core.messages import ToolMessage
+from langgraph.errors import GraphInterrupt
+
+from src.agents.middlewares.tool_error_handling_middleware import ToolErrorHandlingMiddleware
+
+
+def _request(name: str = "web_search", tool_call_id: str | None = "tc-1"):
+    tool_call = {"name": name}
+    if tool_call_id is not None:
+        tool_call["id"] = tool_call_id
+    return SimpleNamespace(tool_call=tool_call)
+
+
+def test_wrap_tool_call_passthrough_on_success():
+    middleware = ToolErrorHandlingMiddleware()
+    req = _request()
+    expected = ToolMessage(content="ok", tool_call_id="tc-1", name="web_search")
+
+    result = middleware.wrap_tool_call(req, lambda _req: expected)
+
+    assert result is expected
+
+
+def test_wrap_tool_call_returns_error_tool_message_on_exception():
+    middleware = ToolErrorHandlingMiddleware()
+    req = _request(name="web_search", tool_call_id="tc-42")
+
+    def _boom(_req):
+        raise RuntimeError("network down")
+
+    result = middleware.wrap_tool_call(req, _boom)
+
+    assert isinstance(result, ToolMessage)
+    assert result.tool_call_id == "tc-42"
+    assert result.name == "web_search"
+    assert result.status == "error"
+    assert "Tool 'web_search' failed" in result.text
+    assert "network down" in result.text
+
+
+def test_wrap_tool_call_uses_fallback_tool_call_id_when_missing():
+    middleware = ToolErrorHandlingMiddleware()
+    req = _request(name="mcp_tool", tool_call_id=None)
+
+    def _boom(_req):
+        raise ValueError("bad request")
+
+    result = middleware.wrap_tool_call(req, _boom)
+
+    assert isinstance(result, ToolMessage)
+    assert result.tool_call_id == "missing_tool_call_id"
+    assert result.name == "mcp_tool"
+    assert result.status == "error"
+
+
+def test_wrap_tool_call_reraises_graph_interrupt():
+    middleware = ToolErrorHandlingMiddleware()
+    req = _request(name="ask_clarification", tool_call_id="tc-int")
+
+    def _interrupt(_req):
+        raise GraphInterrupt(())
+
+    with pytest.raises(GraphInterrupt):
+        middleware.wrap_tool_call(req, _interrupt)
+
+
+@pytest.mark.anyio
+async def test_awrap_tool_call_returns_error_tool_message_on_exception():
+    middleware = ToolErrorHandlingMiddleware()
+    req = _request(name="mcp_tool", tool_call_id="tc-async")
+
+    async def _boom(_req):
+        raise TimeoutError("request timed out")
+
+    result = await middleware.awrap_tool_call(req, _boom)
+
+    assert isinstance(result, ToolMessage)
+    assert result.tool_call_id == "tc-async"
+    assert result.name == "mcp_tool"
+    assert result.status == "error"
+    assert "request timed out" in result.text
+
+
+@pytest.mark.anyio
+async def test_awrap_tool_call_reraises_graph_interrupt():
+    middleware = ToolErrorHandlingMiddleware()
+    req = _request(name="ask_clarification", tool_call_id="tc-int-async")
+
+    async def _interrupt(_req):
+        raise GraphInterrupt(())
+
+    with pytest.raises(GraphInterrupt):
+        await middleware.awrap_tool_call(req, _interrupt)