fix(mcp): classify a cancelled per-server fetch instead of reporting a healthy empty server

A cancelled fetch absorbed to [] made that server contribute ServerListOk(tool_count=0), the exact
healthy-but-empty impostor this change removes. Cancellation stays suppressed (the pre-existing
choice); it now carries an internal fault so outcomes stay truthful

litellm/proxy/_experimental/mcp_server/mcp_server_manager.py

@@ -3393,9 +3393,9 @@ class MCPServerManager:
         except TimeoutError as e:
             verbose_logger.warning(f"Timeout while listing tools from {server_name}")
             raise MCPServerListError(ServerListFault(tag="timeout"), server_name) from e
-        except asyncio.CancelledError:
+        except asyncio.CancelledError as e:
             verbose_logger.warning(f"Task cancelled while listing tools from {server_name}")
-            return []
+            raise MCPServerListError(ServerListFault(tag="internal"), server_name) from e
         except ConnectionError as e:
             verbose_logger.warning(f"Connection error while listing tools from {server_name}: {str(e)}")
             raise MCPServerListError(ServerListFault(tag="unreachable"), server_name) from e

tests/test_litellm/proxy/_experimental/mcp_server/faults/test_list_outcomes.py

@@ -74,3 +74,23 @@ def test_wire_value_carries_no_prose():
 )
 def test_single_upstream_http_status_is_truthful(tag, status_code, expected):
     assert list_fault_http_status(ServerListFault(tag=tag, status_code=status_code)) == expected
+
+
+@pytest.mark.asyncio
+async def test_cancelled_fetch_is_a_classified_fault_not_a_healthy_empty_server():
+    """A cancelled per-server fetch must not masquerade as ok(tool_count=0): cancellation was already
+    suppressed before the outcome plumbing existed, so it stays suppressed, but as an internal fault
+    the outcome reporting can see."""
+    import asyncio
+    from unittest.mock import AsyncMock, MagicMock
+
+    from litellm.proxy._experimental.mcp_server.mcp_server_manager import MCPServerManager
+
+    manager = MCPServerManager()
+    client = MagicMock()
+    client.list_tools = AsyncMock(side_effect=asyncio.CancelledError())
+
+    with pytest.raises(MCPServerListError) as exc_info:
+        await manager._fetch_tools_with_timeout(client, "cancelled_srv")
+
+    assert exc_info.value.fault.tag == "internal"