v0.4.0

The agent-ergonomics release: the slot lifecycle is now fully drivable by orchestrators.

warmtree exec <branch> -- <command...> runs one command inside the slot holding a branch — cwd set, WARMTREE_SLOT in the environment, streams and exit code passed straight through. warmtree exec fix/tests -- npm test behaves like running it there, without the take/cd dance.

warmtree take --scratch claims a slot on a generated scratch/<id> branch for throwaway experiments. The name is picked under the claim lock, so concurrent scratch takes can never collide; the branch name and its release command print on stderr while stdout stays the bare path.

take --json and release --json emit machine-readable results: the take object includes cold, so a harness can tell warm claims from slow fallbacks; the release object reports branch_deleted. Human warnings stay on stderr in both modes.

The agent skill teaches all of it — scratch, json, and when to reach for exec — and every installed copy refreshes automatically on the next warmtree skill or init run, no --force needed.

Also: exec distinguishes its failure modes (127 command-not-found, 126 not-executable, and a broken slot points at warmtree doctor).