Offer PR if remote branch is on a fork

[strawgate]

As we can't push to branches on forks, Let's offer a PR to a fork branch of we're mentioned in a PR that comes from a fork

[github-actions]

2 related issues

• Add PR Review that works with Forks #230 — it already addressed fork-origin pull request handling in the review workflow, so its implementation context may inform how to handle fork-specific limitations here.
• [agent-efficiency] Recurring PR checkout failures in agent workflows (missing remote refs) #307 — it documents fork/head-ref checkout edge cases in PR workflows and includes concrete failure patterns and mitigation ideas that may apply when branch operations differ for forked PRs.

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[github-actions]

tl;dr: The feature is not implemented today; mention-in-pr can’t push to fork branches and currently only tells users to apply changes manually, so I recommend adding a fork fallback that offers create_pull_request to a maintainer branch.

Recommendation

Implement a fork fallback in mention-in-pr workflows: when pull_request_read shows head repo != base repo, switch from “cannot push, ask author to apply manually” to “offer/create a new PR from local validated changes” using create_pull_request.

Findings

• Current behavior explicitly blocks fork pushes and instructs manual author action:
  • .github/workflows/gh-aw-mention-in-pr.md:134
  • .github/workflows/gh-aw-mention-in-pr.md:177-180
  • .github/workflows/gh-aw-fragments/safe-output-push-to-pr.md:85
• mention-in-pr does not currently expose create-PR safe output:
  • imports include push fragment but not create-PR fragment: .github/workflows/gh-aw-mention-in-pr.md:15-21
  • safe outputs only include add-comment/review/push: .github/workflows/gh-aw-mention-in-pr-by-id.md:91-103
• The repo already has a reusable create-PR fragment:
  • .github/workflows/gh-aw-fragments/safe-output-create-pr.md:73-76
  • limitation to call out in UX: base branch is repo default (.github/workflows/gh-aw-fragments/safe-output-create-pr.md:88)
• Reuse precedent exists: mention-in-issue already imports create-PR fragment:
  • .github/workflows/gh-aw-mention-in-issue.md:14

Related history checked:

• Investigate pr merge failure #463 and PR Add pre-push ancestry guard to prevent rewritten PR history #464 improved push/history safety but did not add a fork PR fallback.
• [agent-efficiency] Recurring PR checkout failures in agent workflows (missing remote refs) #307 documents prior PR branch/push fragility in this area.

Verification

I ran available checks/commands relevant to this triage:

$ pytest -q tests/test_safe_input_ready_to_make_pr.py
bash: pytest: command not found

$ uv run pytest -q tests/test_safe_input_ready_to_make_pr.py
bash: uv: command not found

And validated behavior directly from workflow sources via repository search/read (see file+line evidence above).

Detailed Action Plan

1. Enable create-PR safe output in mention-in-pr workflows

   • Update imports in:
     • .github/workflows/gh-aw-mention-in-pr.md
     • .github/workflows/gh-aw-mention-in-pr-no-sandbox.md
     • .github/workflows/gh-aw-mention-in-pr-by-id.md
   • Add gh-aw-fragments/safe-output-create-pr.md alongside existing push/review fragments.

2. Adjust prompt behavior for fork PRs

   • In gh-aw-mention-in-pr*.md instruction sections (currently around fork bullets), replace the fallback guidance:
     • from: “suggest author apply changes manually”
     • to: “offer creating a maintainer-branch PR with the prepared changes via create_pull_request”.

3. Keep branch/base behavior explicit

   • Document in the fork fallback text that created PRs target default branch (current create-PR limitation), so this is an alternate PR path rather than pushing to the contributor fork branch.

4. Regenerate compiled workflows

   • Run compile process so .lock.yml files reflect new safe-output/tool exposure.

5. Validation

   • Add/update workflow-level assertions that gh-aw-mention-in-pr*.lock.yml exposes create_pull_request.
   • Keep existing ready_to_make_pr / ready_to_push_to_pr tests unchanged unless fallback logic is moved into those Python blocks.

Related Items

Type	Link	Relevance
Issue	#485	Requested fork fallback behavior
Issue	#463	Prior push-path investigation (history/merge safety)
PR	#464	Added push guards; no fork create-PR fallback
Issue	#307	Earlier PR checkout/push fragility in this area
File	.github/workflows/gh-aw-mention-in-pr.md:134,177-180	Current fork limitation text
File	.github/workflows/gh-aw-fragments/safe-output-push-to-pr.md:85	Push limitation says manual author fallback
File	.github/workflows/gh-aw-fragments/safe-output-create-pr.md:73-76,88	Existing create-PR capability + default-branch constraint
File	.github/workflows/gh-aw-mention-in-issue.md:14	Existing workflow already reuses create-PR fragment

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