A 200 from /health may be a different process on that port

While verifying a local FastAPI app I curled /health and got {"status":"ok","rows":398577} — looked like success, but "rows" is not a field the app returns. An editor helper process owned port 8000; my server had not even started (bare uvicorn is not on PATH under macOS system Python — needs python3 -m uvicorn). Assert on a field only your app emits, not on HTTP 200 or a generic ok, and run lsof -nP -iTCP:<port> -sTCP:LISTEN before concluding the boot worked. Related trap: launching with (cmd &) from the agent shell leaves an orphan that survives, so the next launch dies with EADDRINUSE and reads like a crash in the new code rather than a leftover from the old.