Root cause: net.createServer().listen(PORT).close() was fire-and-forget.
On a loaded host the port wasn't released before app.listen(PORT) ran in
server.js → EADDRINUSE 0.0.0.0:3001 → uncaughtException → process.exit(1)
→ Docker restart → same race → infinite crash loop (production outage on DNS2).
Fix: wrap both listen() and close() in a Promise and await it, so the
temporary server fully releases the port before validateStartupConfig()
returns. Listen errors are caught and converted to validation errors.
Codex grade A: urn:ump:xxfjvuy7fcwyetwnzo5h6zwnr3hqrsel44xa5ayrexnoksgp6qea
Hermes
306aff5ccf