Auto-request Copilot review on PRs from maintainers

[brendancol]

Problem

Copilot only reviews a PR if a maintainer remembers to request it, and we usually forget. Turning it on for every PR is worse though — drive-by PRs from forks would burn review budget for nothing.

Proposal

A workflow at .github/workflows/copilot-review.yml that asks Copilot for a review when (and only when) the PR author is a maintainer.

Trigger: pull_request_target on opened, reopened, and ready_for_review. pull_request_target rather than pull_request so the job can write to the PR even when it came from a fork.

Gate: check github.event.pull_request.author_association against OWNER, MEMBER, COLLABORATOR. Skip drafts.

Action: gh api POST /repos/{owner}/{repo}/pulls/{pr}/requested_reviewers with reviewers: ["Copilot"].

Permissions: pull-requests: write, nothing else.

Drawbacks

If Copilot review isn't enabled at the org level the API call 4xx's and the run goes red. Noisy but harmless.

Alternatives

• Manual request per PR (status quo, gets forgotten).
• Fire on every PR (defeats the point).

Open question

Re-request on synchronize too, or just once at open? Probably once is enough.