Add ProcessBlockVolumeAssignments to BlockVolumeStore and wire
AssignmentSource/AssignmentCallback into the heartbeat collector's
Run() loop. Assignments are fetched and applied each tick after
status collection.
Bug fixes:
- BUG-CP4B3-1: TOCTOU between GetBlockVolume and HandleAssignment.
Added withVolume() helper that holds RLock across lookup+operation,
preventing RemoveBlockVolume from closing the volume mid-assignment.
- BUG-CP4B3-2: Data race on callback fields read by Run() goroutine.
Made StatusCallback/AssignmentSource/AssignmentCallback private,
added cbMu mutex and SetXxx() setter methods. Lock held only for
load/store, not during callback execution.
7 dev tests + 13 QA adversarial tests = 20 new tests.
972 total unit tests, all passing.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
