Why: the hook landed as 100644, so `make setup` chmod left a mode-only diff that makes the main checkout permanently dirty and blocks task.sh close (dirty-tree guard).
Evidence: git status showed " M scripts/hooks/post-merge" with 0 insertions/deletions after make setup; task-finish tail reported the dirty-tree refusal.
Impact: mode 100644 -> 100755 only; no content change.
Refs: task card feature/card-autoclose-r1 (PR #16 follow-up)