Library generation failed (3b86441)

See [failed job](https://github.com/googleapis/google-cloudevents-java/actions/runs/17875741220)

Start with the linked failed job at https://github.com/googleapis/google-cloudevents-java/actions/runs/17875741220 and identify which library-generation step failed. Trace that failure to the relevant build or generation entry point; done means the library generation job completes successfully.

索引モデルが issue の本文から書いたものです。