feat: add NIP-52 event sync from Nostr relays

Subscribe to kind 31922/31923 events and upsert into local DB:
- New events discovered from relays are auto-approved
- Existing events are updated if incoming version is newer
- Deduplication via event ID and d-tag correlation
- Events from Nostr have empty wallet (not ticketed locally)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

nostr_sync.py

@@ -0,0 +1,170 @@
+"""
+Bidirectional Nostr sync for the events extension.
+
+Subscribes to NIP-52 calendar events (kind 31922/31923) from relays
+and upserts them into the local database. Enables federated event
+discovery — events published by other LNbits instances or Nostr
+clients appear in the local events listing.
+"""
+
+import json
+from datetime import datetime, timezone
+
+from loguru import logger
+
+from .crud import create_event, db, get_event, update_event
+from .models import CreateEvent, Event
+from .nostr.nostr_client import NostrClient
+
+
+async def process_nostr_message(nostr_client: NostrClient, message: str):
+    """Process an incoming Nostr relay message."""
+    try:
+        data = json.loads(message)
+    except json.JSONDecodeError:
+        return
+
+    if not isinstance(data, list) or len(data) < 2:
+        return
+
+    msg_type = data[0]
+
+    if msg_type == "EVENT" and len(data) >= 3:
+        event_data = data[2]
+        await _handle_calendar_event(nostr_client, event_data)
+    elif msg_type == "EOSE":
+        logger.debug("[EVENTS] End of stored events from relay")
+    elif msg_type == "NOTICE":
+        logger.info(f"[EVENTS] Relay notice: {data[1]}")
+
+
+async def _handle_calendar_event(nostr_client: NostrClient, event_data: dict):
+    """Handle an incoming NIP-52 calendar event (kind 31922 or 31923)."""
+    kind = event_data.get("kind")
+    if kind not in (31922, 31923):
+        return
+
+    event_id = event_data.get("id", "")
+    if nostr_client.is_duplicate_event(event_id):
+        return
+
+    tags = {t[0]: t[1] for t in event_data.get("tags", []) if len(t) >= 2}
+    tag_lists = {}
+    for t in event_data.get("tags", []):
+        if len(t) >= 2:
+            tag_lists.setdefault(t[0], []).append(t[1])
+
+    d_tag = tags.get("d")
+    if not d_tag:
+        return
+
+    title = tags.get("title", "Untitled Event")
+    start = tags.get("start")
+    if not start:
+        return
+
+    end = tags.get("end")
+    description = event_data.get("content", "")
+    image = tags.get("image")
+    location = tags.get("location")
+    categories = tag_lists.get("t", [])
+
+    # Check if we already have this event (by d-tag as our event ID
+    # or by nostr_event_id)
+    existing = await get_event(d_tag)
+    if not existing:
+        # Check by nostr_event_id
+        existing = await db.fetchone(
+            "SELECT * FROM events.events WHERE nostr_event_id = :nid",
+            {"nid": event_id},
+            Event,
+        )
+
+    if existing:
+        # Update if the incoming event is newer
+        incoming_created_at = event_data.get("created_at", 0)
+        if (
+            existing.nostr_event_created_at
+            and incoming_created_at <= existing.nostr_event_created_at
+        ):
+            return  # We already have a newer version
+
+        existing.name = title
+        existing.info = description
+        existing.event_start_date = start
+        existing.event_end_date = end
+        existing.banner = image
+        existing.location = location
+        existing.categories = categories
+        existing.nostr_event_id = event_id
+        existing.nostr_event_created_at = incoming_created_at
+        await update_event(existing)
+        logger.info(f"[EVENTS] Updated event from Nostr: {title}")
+    else:
+        # Create new event from Nostr
+        # Events discovered from Nostr are auto-approved (they're already public)
+        event = CreateEvent(
+            wallet="",  # No wallet — discovered from Nostr, not ticketed locally
+            name=title,
+            info=description,
+            event_start_date=start,
+            event_end_date=end,
+            banner=image,
+            location=location,
+            categories=categories,
+            status="approved",
+        )
+        # Use the d-tag as the event ID for correlation
+        from lnbits.db import Database
+
+        new_event = Event(
+            id=d_tag,
+            wallet="",
+            name=title,
+            info=description,
+            event_start_date=start,
+            event_end_date=end,
+            banner=image,
+            location=location,
+            categories=categories,
+            status="approved",
+            time=datetime.now(timezone.utc),
+            nostr_event_id=event_id,
+            nostr_event_created_at=event_data.get("created_at", 0),
+        )
+        try:
+            await db.insert("events.events", new_event)
+            logger.info(f"[EVENTS] Discovered event from Nostr: {title}")
+        except Exception as e:
+            # Likely duplicate key — skip
+            logger.debug(f"[EVENTS] Skipped duplicate event: {e}")
+
+
+async def wait_for_nostr_events(nostr_client: NostrClient):
+    """
+    Background task: subscribe to NIP-52 events and process them.
+    """
+    logger.info("[EVENTS] Starting Nostr event sync...")
+
+    while True:
+        try:
+            # Subscribe to NIP-52 calendar events
+            await nostr_client.subscribe([
+                {"kinds": [31922, 31923]},
+            ])
+
+            # Process incoming events
+            while True:
+                message = await nostr_client.get_event()
+                await process_nostr_message(nostr_client, message)
+
+        except ValueError:
+            # WebSocket closed — will reconnect
+            logger.warning("[EVENTS] Nostr connection lost, resubscribing...")
+            await asyncio.sleep(10)
+        except Exception as e:
+            logger.error(f"[EVENTS] Nostr sync error: {e}")
+            await asyncio.sleep(30)
+
+
+import asyncio  # noqa: E402