When the `require_issue_link` workflow closes a PR and posts an
enforcement comment, that comment was never cleaned up after the
situation resolved — leaving a stale "automatically closed" message
visible on reopened PRs. Now all three resolution paths (maintainer
bypass, author fixing the issue link, and contributor assignment)
minimize the enforcement comment as outdated via GraphQL. The cleanup is
best-effort: failures log a warning but never block the primary workflow
logic (label removal, bypass, reopen).
`require_issue_link.yml` auto-closes external PRs when the author isn't
assigned to the linked issue, but there was no trigger to reopen them
when a maintainer later grants the assignment. Contributors had to
manually edit their PR description to trigger re-evaluation — poor UX
that generated repeat questions. This adds a companion workflow that
listens for issue assignment events and reopens matching PRs
automatically.
The `require_issue_link` workflow's maintainer override (reopen PR or
remove `missing-issue-link` to bypass enforcement) has never worked. It
calls `orgs.getMembershipForUser` to verify the sender is an org member,
but `GITHUB_TOKEN` is a GitHub App installation token — not an org
member — so the endpoint always returns 403. The catch block only
handled 404, so the unhandled 403 crashed the entire job, blocking even
the normal issue-link validation from running.
## Changes
- Replace `orgs.getMembershipForUser` with
`repos.getCollaboratorPermissionLevel` in `senderIsOrgMember()` — checks
if the event sender (the user who reopened the PR or removed the label)
has write/maintain/admin access on the repo, which works with
`GITHUB_TOKEN` and is a better proxy for "maintainer" than org
membership
