Why: 11 merged branches had left their task cards open (bookkeeping debt found on 2026-09-30); closure was manual and never triggered, so card status rotted after each merge.
Evidence: dogfood run of `task.sh close --fold` closed and archived the 11 cards (previous commit); temp-repo matrix 33/33 PASS covering detection, pending-branch idempotence, dirty/no-fold refusals, post-merge auto-close on merge-type pulls, worktree guard, and the full lifecycle (closure PR merge archives cards on main).
Impact: scripts/task.sh (+close, precheck [cards] report, finish-tail trigger), scripts/hooks/post-merge (new), Makefile (+task-close target, setup chmod), AGENTS.md rule; archive fixes correct PR links missed by the first dogfood run; no module or gitlink change.
Refs: task card feature/card-autoclose-r1
weichen
beaefb7549