firehose: Deleting bin/firehose.dart broke pinned publish.yaml@<sha> #478

Repositories pinned to dart-lang/ecosystem/.github/workflows/publish.yaml@<sha> fail both PR publish / validate checks and tag-triggered publish / publish releases with Could not find bin/firehose.dart in package firehose (exit 66) after #454.

• Root cause: Historical publish.yaml revisions activate package:firehose from unpinned main rather than job.workflow_sha in both validate (publish.yaml#L154-L156) and publish (publish.yaml#L273-L275) before invoking dart pub global run firehose.
• Impact: Unmigrated repositories pinned to publish.yaml@<sha>, such as dart-lang/tools/.github/workflows/publish.yaml#L17, fail publish / validate on every PR and cannot publish <pkg>-vX.Y.Z release tags until migrated.

Possible Directions

• Restore bin/firehose.dart and its validate / publish entrypoints on main temporarily until downstream repositories finish migrating off publish.yaml@<sha>.
• Document or track the migration for remaining publish.yaml@<sha> and publish.yaml@main callers.

Uses: dart-lang/ecosystem/.github/workflows/publish.yaml@e1d4a04b8d1cff6214a7861c59140aad0d93636b
...
Run dart pub global activate --source git https://github.com/dart-lang/ecosystem --git-path pkgs/firehose/
+ firehose 0.13.2-wip from git https://github.com/dart-lang/ecosystem at 78abf7 in pkgs/firehose
Installed executables comment, groundskeeper and health.
...
dart pub global run firehose --validate --no-use-flutter --ignore-packages "" --tag-prefix "v"
Could not find bin/firehose.dart in package firehose.
Error: Process completed with exit code 66.