Copilot's third pass (suppressed comment) caught the remaining hole in the
child-process handling: `spawn()` reports a failure to start via an `error`
event, not `exit`. With no `error` listener Node throws it uncaught, replacing
the smoke's diagnostic with a raw stack — and because `exit` never fires in that
case, the readiness poll would otherwise spin for the full 30s before reporting
a timeout that misattributes the cause. `close` is now listened to alongside
`exit` for the same reason: it fires in cases `exit` does not.
prod-web-server.mjs already documents this exact hazard for the launcher child;
this brings the test-server child in line.
Both new branches verified by hand:
- unspawnable executable → "could not spawn the MCP test server (…): spawn
/nonexistent/node-binary ENOENT", immediately, instead of an uncaught throw
- missing module → "MCP test server exited early" with the loader stack, fast,
with no 30s hang
Full `npm run ci` green.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XAR2Nr9kXbrywFNUVoTe9F
5401e527e6