Tool functions raise KeyError for unknown ids and ValueError for invalid
state transitions. Without handlers, FastAPI returned a bare 500
"Internal Server Error" to MCP clients — useless for an agent that needs
to know whether the id was wrong vs the cluster was down.
KeyError -> 404 with the message ("Unknown job_id: foo").
ValueError -> 400 with the message (e.g. "pending_id p_xyz is in status
'CANCELLED', not PENDING").
The plan's route signatures used query parameters, which worked for direct
HTTP callers and unit tests, but fastapi-mcp's HTTP transport passes
tools/call arguments as a JSON body. dict-typed parameters like
spark_conf arrived as a string and the route returned 422.
Refactor each route to take a single Pydantic body model (saved in
spark_executor/tools/requests.py). Underlying tool functions unchanged.
Integration tests in tests/integration/test_mcp_routes.py now exercise
the full body-based roundtrip (save_connection with spark_conf, prepare
→ list → get, list_connections with empty body).
Claude