Merges every queued PR into a throwaway detached worktree cut from origin/<base>,
runs the fast-gates parity suite ONCE on the final train tip, and prints the
evidence line that authorizes gh pr merge --squash --admin per member
(merge-gates.md §7). Conflicting PRs are ejected and reported, the train
continues. Never pushes, never merges PRs, never stashes.
