Rotation: history compaction and leak recovery

A skein’s automerge document keeps full history forever, and its doc id is an irrevocable capability. braid rotate addresses both: it exports the current state into a fresh document (shedding history), marks the old document rotated, and switches your .braid.toml. Stale clones get a clear error and run braid rotate --adopt to follow; changes they made after the cutover are detected and written to .braid-stragglers.jsonl for review and re-import.

If the doc id has leaked, use braid rotate --revoke: identical mechanics, except no forwarding pointer is written into the old document (the attacker can read it — a pointer would hand them the new capability). Distribute the new secret out-of-band with braid secret.

Honest limits: rotation protects future reads and writes. The old document’s history remains readable forever to anyone holding the old id; revocation cannot un-leak the past.