Book Preview PR workflow fails on fork PRs when posting preview comment

[thepastaclaw]

Summary

The Book Preview (PR) workflow can build the preview successfully but still fail on fork-origin pull requests when the final actions/github-script step tries to create/update a PR comment.

Observed on dashpay/platform#3092:

• Failing job: https://github.com/dashpay/platform/actions/runs/25755548133/job/75642901180
• PR head repository: thepastaclaw/platform
• Failure step: Post preview link
• Build itself succeeded; the failure is only the comment-posting step.

Failure mode

The workflow calls github.rest.issues.createComment / updateComment from a pull_request run:

RequestError [HttpError]: Resource not accessible by integration
status: 403
x-accepted-github-permissions: issues=write; pull_requests=write

Current upstream/v3.1-dev:.github/workflows/book-preview.yml grants:

permissions:
  contents: read
  pull-requests: write

Two problems combine here:

1. Issue comments require issues: write, not just pull-requests: write.
2. For PRs from forks, the pull_request workflow token is read-only anyway, so the comment step cannot be relied on even if workflow permissions are adjusted.

Suggested fix

Do not fail the preview build when the comment cannot be posted. Options:

• guard the comment step to same-repo PRs only, or
• catch 403s in the github-script and log a warning, or
• mark only the comment step continue-on-error: true.

Avoid switching this build workflow directly to pull_request_target with write credentials while checking out/building untrusted PR code.

Impact

Any fork PR touching book/** can get a red Build book preview check even though mdbook build book succeeds.

[thepastaclaw]

This appears to be covered by existing PR #3635: #3635

That PR keeps the workflow on pull_request, adds the missing issues: write, and catches the fork-token 403 Resource not accessible by integration case so a successful preview build does not go red solely because the comment step cannot write. CI on #3635 is currently green.