LibreOffice supervisor returns cached first-start error on every subsequent request #1538

Summary

If LibreOffice fails to start on the first request (e.g. libreoffice-start-timeout is exceeded), the supervisor caches the error and every subsequent request fails immediately with the same error until the container is restarted.

Affected versions

8.27.0 through main. Verified that the issue is not present in 8.26.0 (each request retried the launch until it succeeded).

The regression appears to be related to #1467, which reworked the supervisor to support concurrency.

Reproduction

1. Run Gotenberg with --libreoffice-start-timeout=1s (or any duration shorter than LibreOffice's actual cold start on the host).

2. Send a request to /forms/libreoffice/convert. It fails after the timeout with:

   convert to PDF: supervisor run task: process first start: start process: execute LibreOffice: context done: context deadline exceeded

3. Send another request. It fails immediately with the same error.

The supervisor stays in this state for the rest of the container's lifetime.