Landing an official GitHub PR stack

Land dependent PRs through GitHub's native stack object and gh stack merge. Do not reproduce stack semantics by merging and retargeting individual PRs with gh pr merge and gh pr edit.

Require native stack support

Run gh stack --version before changing GitHub state. Hard-stop if the official extension or server-side stack feature is unavailable; do not fall back to manually merging and retargeting PRs one at a time. GitHub stacks require every head branch to live in the same repository, so hard-stop on a cross-fork chain.

Use a clean dedicated worktree. Fetch current PR metadata and exact head OIDs rather than trusting branch names or an earlier report:

gh pr view <pr> --json number,author,baseRefName,baseRefOid,headRefName,headRefOid,isCrossRepository,state,isDraft,reviewDecision,mergeStateStatus,statusCheckRollup

Query PullRequest.stack and stackEntry.position for at least one PR in each apparent chain; this official GitHub object, not base-branch inference alone, is the stack-membership authority. Paginate entries when size exceeds the returned page: