feat: background tasks — settle on payment, expire holds

Payment (not any nostr event) is the commit point: the invoice listener
promotes held/awaiting_payment bookings to confirmed, hard-blocks the
dates, and republishes the encrypted reservation object. expire_holds_loop
sweeps lapsed holds every minute so abandoned requests free their dates.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019VUQCfdqiLSsFS2jcGnaFD

tasks.py

@@ -0,0 +1,59 @@
+"""Background tasks: settle paid bookings, expire stale holds.
+
+Payment is what promotes a booking from `held`/`awaiting_payment` to
+`confirmed` — not any Nostr event. We listen on the LNbits invoice
+dispatcher (same pattern as lnurlp/spirekeeper), and separately sweep
+expired holds so abandoned requests free their dates.
+"""
+
+import asyncio
+
+from lnbits.core.models import Payment
+from lnbits.tasks import register_invoice_listener
+from loguru import logger
+
+from . import crud
+from .models import BookingStatus
+from .nostr import service as nostr
+
+
+async def wait_for_paid_invoices():
+    invoice_queue: asyncio.Queue = asyncio.Queue()
+    register_invoice_listener(invoice_queue, "ext_chatelet")
+    while True:
+        payment = await invoice_queue.get()
+        await on_invoice_paid(payment)
+
+
+async def on_invoice_paid(payment: Payment):
+    if not payment.extra or payment.extra.get("tag") != "chatelet":
+        return
+    booking = await crud.get_booking_by_payment_hash(payment.payment_hash)
+    if not booking:
+        logger.warning(f"chatelet: paid invoice with no matching booking: {payment.payment_hash}")
+        return
+    if booking.status not in (BookingStatus.held, BookingStatus.awaiting_payment):
+        return  # already settled / cancelled — ignore duplicate settle
+
+    # Payment confirms the booking: hard-block the dates, clear the hold,
+    # publish the updated reservation object + send check-in details.
+    booking.status = BookingStatus.confirmed
+    booking.expires_at = None
+    await crud.update_booking(booking)
+    booking.reservation_event_id = await nostr.publish_reservation(booking)
+    await crud.update_booking(booking)
+    # TODO(checkin): DM check-in details (address, gate code, times) to the
+    # guest via NIP-17 giftwrap once relay plumbing lands.
+    logger.info(f"chatelet: booking {booking.id} confirmed")
+
+
+async def expire_holds_loop():
+    """Sweep lapsed holds every minute so abandoned requests free dates."""
+    while True:
+        try:
+            expired = await crud.expire_stale_holds()
+            for b in expired:
+                logger.debug(f"chatelet: hold {b.id} expired, dates freed")
+        except Exception as exc:  # noqa: BLE001
+            logger.error(f"chatelet: hold-expiry sweep failed: {exc}")
+        await asyncio.sleep(60)