Dispatch — spawn a confined worker

One spawn shape, for every harness. The drive cadence lives in the /dispatch router; this skill is the spawn call plus the landing mechanics.

The worker is confined by the OS, not by cooperation. Inside the namespace only its own worktree and the harness's config dir are writable; everything else — the coordination tree, sibling forks, .doctrine/, and the real git dir — is read-only. So the worker cannot commit at all, and its hand-back is an uncommitted working tree that the orchestrator imports. Never instruct a worker to commit.

Spawn

scripts/spawn-confined.sh <harness> <B> <BRANCH> <DIR> <PROMPT_FILE> [BACKSTOP_SECS]