bug: gift wrap subscription reconnect causes missed messages (no backfill on reconnect)

[islandbitcoin]

Summary

When the gift wrap subscription (fetchGiftWrapsForPublicKey) drops and reconnects, any NIP-17 gift wraps published during the reconnect window are permanently missed. There is no backfill mechanism to catch up on events received while the subscription was down.

Root Cause

In app/utils/nostr.ts, the subscription reconnect logic re-establishes the connection but starts listening from now with no since filter:

onclose: () => {
  closer.close()
  closer = fetchGiftWrapsForPublicKey(pubkey, eventHandler, pool)
},

The new subscription call has no since timestamp, so any events published during the gap between close and reconnect are never fetched.

Impact

• Messages sent while the recipient's subscription is reconnecting are silently dropped
• Manifests as "Missed a note" / "Missed N notes" in the chat UI
• Intermittent — depends on relay connection stability and timing
• Observed during QA testing of PR QOL features on chat #579

Suggested Fix

Track the last event timestamp received (lastSeenAt) and pass it as a since filter on reconnect:

let lastSeenAt = Math.floor(Date.now() / 1000)

onclose: () => {
  closer.close()
  closer = fetchGiftWrapsForPublicKey(pubkey, eventHandler, pool, lastSeenAt)
},

// In the subscription:
onevent: (event) => {
  lastSeenAt = Math.max(lastSeenAt, event.created_at)
  eventHandler(event)
}

This ensures reconnects backfill any events missed during the gap.

Steps to Reproduce

1. Open two accounts in chat (iOS simulator + Android emulator)
2. Send messages back and forth rapidly
3. Observe "Missed a note" appearing on one side
4. Check Metro logs — subscription reconnect events coincide with missed messages

References

• PR QOL features on chat #579 (where this was observed during QA)
• NIP-17 gift wrap spec