feat(purgatory): track expired events to prevent infinite re-sync loops

Adds expired event tracking to prevent proactive sync from repeatedly
fetching and re-adding events that expired from purgatory without
finding git data.

Key features:
- Track expired events for 7 days to prevent re-sync loops
- Distinguish synced vs user-submitted events (via socket address)
- Allow users to retry expired events (git data might now be available)
- Reject synced expired events (prevents infinite loop)
- Daily cleanup of expired event records older than 7 days

Implementation:
- Added expired_events: DashMap<EventId, Instant> to Purgatory
- Updated event_ids() to include both purgatory + expired events
- Added is_expired(), mark_expired(), cleanup_expired_events()
- Updated cleanup() to mark expired events automatically
- Added is_synced detection in WritePolicy (localhost:0 = synced)
- Policy layer checks is_synced && is_expired() before rejecting

Behavior:
- Negentropy: Filters expired events before fetching (optimal)
- REQ+EOSE: Rejects synced expired events at policy layer
- User submissions: Always allowed to retry (skip expired check)

Testing:
- Added 5 new tests for expired event tracking
- All 222 tests passing

Fixes the infinite re-sync loop where events without git data would
expire, get synced again, expire again, repeat forever.

0 files changed, 0 insertions, 0 deletions