Loop A (refactor) log

Goal: extract retry/backoff helpers; rename types.

Phase 1 (no coordination)

• Edited shared files in src/api/** with no lock; collided with the other loop.
• Several passes re-did work that the other loop had clobbered.

Phase 2 (lease dir + heartbeat/TTL + merge-queue)

• Acquire a lease on the path glob before editing; heartbeat every 30s; TTL 120s.
• On LOCK DENIED, BACKOFF(30s) and retry. Land via the merge queue.
• Result: zero conflicts.