Auto-assign PR author, and credit PR author on issue close

[aglinxinyuan]

Task Summary

Improve assignee handling on issues and PRs so that (a) PRs always have an obvious owner and (b) closed issues always reflect who actually shipped the fix.

Behavior

For PRs — auto-assign the author when the PR is opened, reopened, or moved to ready-for-review. Skip bots (e.g. dependabot[bot]) and PRs that already have an assignee.

For issues — do not auto-assign on creation. New issues stay unassigned and keep the existing triage label (handled by issue-triage.yml) because triage is a deliberate human decision; auto-assigning the reporter would short-circuit it.

On PR merge — when a PR is merged that closes one or more issues (via Closes #N / Fixes #N / Resolves #N keywords or the sidebar "Linked issues" relationship), assign the PR author to those issues, replacing any existing assignees. This gives credit to whoever actually shipped the work — e.g. if A was originally assigned to issue X but B steps in and lands the fix, B becomes the assignee on X when the PR merges.

Why

• New PRs from external contributors currently have no clear owner, slowing review routing.
• Closed-by-PR issues sometimes still show an outdated assignee (the original triager) rather than the person who shipped, which makes credit and history less useful.
• Triage shouldn't be skipped by auto-assigning the reporter — leaving issues unassigned keeps the triage workflow doing its job.

Priority

P2 – Medium

Task Type

• Code Implementation
• Documentation
• Refactor / Cleanup
• Testing / QA
• DevOps / Deployment

[Yicong-Huang]

For PRs yes, let's make the author assignee.

For issues, I think it's better to leave it not assigned. it is not a good idea to assign the issue to a reporter. An issue requires triage. So I suggest this:

1. leave it empty for a new issue. and the triage label is marked. It is actually intentional to leave it unassigned, because we need to triage it.
2. Once a linked PR is merged and closed an issue, assign the PR author to that issue to give credit. This may also overwrites the original assignee: if A is assigned to do an issue X, but B steps out to finish it and closed it with PR, then B should be changed to assignee to give B credit.

[aglinxinyuan]

Agree. I didn't think about the issue carefully.

[aglinxinyuan]

• New issues stay unassigned and keep the triage label (issue-triage.yml already handles this).
• On PR merge, a new credit-issue-on-pr-merge job uses GitHub's
  closingIssuesReferences (Closes/Fixes/sidebar-linked) to find the
  linked issues and replaces their assignees with the PR author so
  credit goes to whoever actually shipped it.

[chenlica]

Who should be the author of this issue about authors of issues? :-)