Add ticket +/- quantity support to shared contracts and services

- Add ticket_type_id field to TicketDTO for grouping
- Add adjust_ticket_quantity to CalendarService protocol + SQL impl
- Add stub for adjust_ticket_quantity

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

services/calendar_impl.py

@@ -72,6 +72,7 @@ def _ticket_to_dto(ticket: Ticket) -> TicketDTO:
         created_at=ticket.created_at,
         checked_in_at=ticket.checked_in_at,
         entry_id=entry.id if entry else None,
+        ticket_type_id=ticket.ticket_type_id,
         price=price,
         order_id=ticket.order_id,
         calendar_container_id=cal.container_id if cal else None,
@@ -563,3 +564,59 @@ class SqlCalendarService:
         )
         for ticket in result.scalars().all():
             ticket.user_id = user_id
+
+    async def adjust_ticket_quantity(
+        self, session: AsyncSession, entry_id: int, count: int, *,
+        user_id: int | None, session_id: str | None,
+        ticket_type_id: int | None = None,
+    ) -> int:
+        """Adjust reserved ticket count to target. Returns new count."""
+        import uuid
+
+        count = max(count, 0)
+
+        # Current reserved count
+        filters = [
+            Ticket.entry_id == entry_id,
+            Ticket.state == "reserved",
+        ]
+        if user_id is not None:
+            filters.append(Ticket.user_id == user_id)
+        elif session_id is not None:
+            filters.append(Ticket.session_id == session_id)
+        else:
+            return 0
+        if ticket_type_id is not None:
+            filters.append(Ticket.ticket_type_id == ticket_type_id)
+
+        current = await session.scalar(
+            select(func.count(Ticket.id)).where(*filters)
+        ) or 0
+
+        if count > current:
+            # Create tickets
+            for _ in range(count - current):
+                ticket = Ticket(
+                    entry_id=entry_id,
+                    ticket_type_id=ticket_type_id,
+                    user_id=user_id,
+                    session_id=session_id,
+                    code=uuid.uuid4().hex,
+                    state="reserved",
+                )
+                session.add(ticket)
+            await session.flush()
+        elif count < current:
+            # Cancel newest tickets
+            to_cancel = current - count
+            result = await session.execute(
+                select(Ticket)
+                .where(*filters)
+                .order_by(Ticket.created_at.desc())
+                .limit(to_cancel)
+            )
+            for ticket in result.scalars().all():
+                ticket.state = "cancelled"
+            await session.flush()
+
+        return count

services/stubs.py

@@ -132,6 +132,11 @@ class StubCalendarService:
     ) -> None:
         pass
 
+    async def adjust_ticket_quantity(
+        self, session, entry_id, count, *, user_id, session_id, ticket_type_id=None,
+    ) -> int:
+        return 0
+
     async def entry_ids_for_content(self, session, content_type, content_id):
         return set()