fix(mcp): Improve validation errors and field aliases to reduce failed LLM tool calls (#38625)

tests/unit_tests/mcp_service/utils/test_schema_utils.py

@@ -481,10 +481,12 @@ class TestParseRequestDecorator:
             result = sync_tool('{"name": "test", "count": 5}', extra="data")
         assert result == "test:5:data"
 
-    def test_decorator_raises_validation_error_async(self):
-        """Should raise ValidationError for invalid data in async function."""
+    def test_decorator_raises_tool_error_for_invalid_data_async(self):
+        """Should raise ToolError with field details for invalid data."""
         from unittest.mock import MagicMock, patch
 
+        from fastmcp.exceptions import ToolError
+
         @parse_request(self.RequestModel)
         async def async_tool(request, ctx=None):
             return f"{request.name}:{request.count}"
@@ -493,20 +495,22 @@ class TestParseRequestDecorator:
 
         mock_ctx = MagicMock()
         with patch("fastmcp.server.dependencies.get_context", return_value=mock_ctx):
-            with pytest.raises(ValidationError):
+            with pytest.raises(ToolError, match="Required fields for RequestModel"):
                 asyncio.run(async_tool('{"name": "test"}'))  # Missing count
 
-    def test_decorator_raises_validation_error_sync(self):
-        """Should raise ValidationError for invalid data in sync function."""
+    def test_decorator_raises_tool_error_for_invalid_data_sync(self):
+        """Should raise ToolError with field details for invalid data."""
         from unittest.mock import MagicMock, patch
 
+        from fastmcp.exceptions import ToolError
+
         @parse_request(self.RequestModel)
         def sync_tool(request, ctx=None):
             return f"{request.name}:{request.count}"
 
         mock_ctx = MagicMock()
         with patch("fastmcp.server.dependencies.get_context", return_value=mock_ctx):
-            with pytest.raises(ValidationError):
+            with pytest.raises(ToolError, match="Required fields for RequestModel"):
                 sync_tool('{"name": "test"}')  # Missing count
 
     def test_decorator_with_complex_model_async(self):