tracecraft demo: zero-credential tour in 30 seconds

[Arrmlet]

Problem

Trying tracecraft today requires a bucket and credentials before you see anything work. That's the right bar for production, but too high for "show me."

Proposal

tracecraft demo — no credentials, no network: an ephemeral local directory implementing the same store interface (atomic create via O_EXCL standing in for S3 If-None-Match), running a scripted three-act episode:

1. Record — an agent writes memory, sends a message, mirrors a synthetic session… then dies.
2. Recover — a fresh process reads everything back and replays the session.
3. Coordinate — two agents race to claim the same step; exactly one wins, the loser picks the next task, hands off with a note.

Ends by printing the bucket tree it created and a pointer: production cross-host atomicity requires a real S3 conditional-write backend.