#219 Replay: Handle timer race conditions with event delivery

## Problem When workflow sleeps, if event arrives before wake time, ordering is not guaranteed. ## Scenario - Workflow calls ctx.sleep(60) - Event arrives at t+30 via emit_event() - Both available_at and event wake mechanisms trigger ## Gap - No guarantee on execution order - Different path on replay vs production possible - Non-deterministic behavior ## Impact - Subtle bugs in timer + event workflows - Replay may diverge from original execution ## Solution 1. Document expected behavior clearly 2. Add ordering guarantees (event takes priority?) 3. Log which wake mechanism was used 4. Validate in replay that same mechanism used ## Effort: Medium