Capture pre-skill-apply XP and perk snapshots; on TryRecord loss reverse each applied skill row via negative delta and restore the perk snapshot so level-up unlocks from the loser call are reverted without clobbering a concurrent winner's XP.
Mirror EncounterCompletionOperations compensating rollback: concurrent losers undo item and skill XP applies before returning the winner event.
Apply item grants and mission_reward skill XP with compensating rollback, idempotent IRewardDeliveryStore recording, and AAA integration tests.
VinPropane