Worktree isolation

Worktree isolation is giving each parallel agent its own checked-out directory over one shared object store. It works for what it claims — separate files, separate branches, no lock contention — and it is not a security boundary, which is the half nobody repeats. Git's own repository-layout documentation is explicit about the shared half: objects, hooks, config, packed-refs and every ref outside bisect, rewritten and worktree all resolve to the common directory instead of the worktree's own. So an agent inside a worktree can install a pre-commit hook that runs as you on your next commit. The usual objection to cloning instead — that it is slow — does not hold at the repository sizes anyone here works at. Worktree when a person drives; clone when something else does.