Replace `git show HEAD:.planning/STATE.md` with `cp .planning/STATE.md`
in the worktree merge-back protection logic of execute-phase.md and
quick.md. The git show approach exits 128 when STATE.md has uncommitted
changes or is not yet in HEAD's committed tree, leaving an empty backup
and causing the post-merge restore guard to silently skip — zeroing or
staling the file. Using cp reads the actual working-tree file (including
orchestrator updates that haven't been committed yet), which is exactly
what "main always wins" should protect.