Library generation failed (f898e26)

See [failed job](https://github.com/googleapis/google-cloudevents-java/actions/runs/17171623344)

Start with the linked failed job at GitHub Actions run 17171623344 and identify the library-generation step and its failure output. Trace that step to the relevant project entry point; done means the generation job completes successfully.

索引モデルが issue の本文から書いたものです。