Use pull request safe git_ref and git_commit in GitHub Actions examples

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Background

As noted in an old CaC document, the GitHub variables available during a GitHub Action differ between some of he events.

On a pull_request event those two values are refs/pull/<number>/merge and the merge commit GitHub creates for the pull request. That commit is not reachable from any branch or tag, so the release is pinned to a commit that Octopus can later fail to resolve. It also disagrees with what the workflow actually built, because a build normally checks out the branch head.

The Creating releases from a build server plugin page already warns about this but isn't completely accurate. The GitHub Actions page did not, and its examples are the ones people copy.

Without this specific configuration, a CaC deployment can fail as the branch specified with just github.ref may reference the merge branch that is removed post-merge.
E.g the error we see is along the lines of

No git resource with the name '718841c5...' exists in the repository.`

GitHub Variables

Commit Sha

Variable / Context	Push Events	Pull Request Events	What does it point to?
github.sha	Yes	Yes	push: The latest commit on the branch. pull_request: A temporary ⚠️, simulated merge commit (refs/pull/PR_NUMBER/merge).
github.event.pull_request.head.sha	No (Null)	Yes	The actual latest commit pushed to the source/feature branch of the PR.
github.event.push.after / github.event.after	Yes	No (Null)	The HEAD commit SHA of the branch after the push was executed.

Ref

Variable / Context	Push Events	Pull Request Events	Availability
github.ref	Branch or tag pushed (refs/heads/main)	PR merge ref (refs/pull/:num/merge)	Always available
github.head_ref	Empty ("")	Source branch name (e.g., feature-branch)	Only on pull_request / pull_request_target

Results

github-actions.mdx

• All three create-release examples now use git_ref: ${{ github.head_ref || github.ref }} and git_commit: ${{ github.event.pull_request.head.sha || github.sha }}. Both expressions fall back to the push values on every other event, so the examples still work unchanged for workflow_dispatch, push, and schedule.
• Added a hint after the first example explaining why the pull request values differ.
• Expanded the git_ref and git_commit input descriptions to say the same thing in the table.

creating-release-from-a-build-server-plug-in.mdx

• Fixed the Git Commit expression. It read ${{ github.event.push.after || github.event.pull_request.head.sha }}, but a push payload exposes the commit as github.event.after, so github.event.push.after was always empty and a push fell through to the pull request value. It now reads ${{ github.event.pull_request.head.sha || github.sha }}.
• Replaced the note about manually triggered runs, because the new expression covers them.

Testing

Documentation only, no code changes. Both files render as MDX with existing syntax, and the hint uses the same :::div{.hint} block already used on the TeamCity page.

Verified the underlying claim against the live GitHub API for the pull request in the original report. The merge commit exists only on refs/pull/282/merge, and the branch head is a different commit.

🤖 Generated with Claude Code

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Pull request environment is available at https://stoctodocspr3462.z22.web.core.windows.net/.

You can view the ephemeral environment status in Octopus Deploy.

This environment will be automatically deprovisioned when the pull request is closed, or after 7 days of inactivity.

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Updating our docs around GitHub references to use for CaC projects