fix: harden booking and meeting flows

lib/booking/lock.ts

@@ -13,13 +13,14 @@ import type { PayloadRequest } from "payload";
  */
 export async function acquireBookingDayLock(req: PayloadRequest, dateKey: string): Promise<void> {
   const txID = req.transactionID ? String(await req.transactionID) : undefined;
-  if (!txID) return; // No active transaction — nothing to lock against.
+  if (!txID) throw new Error("A booking lock requires an active transaction");
 
   const adapter = req.payload.db as unknown as {
     sessions?: Record<string, { db: { execute: (query: unknown) => Promise<unknown> } }>;
     drizzle: { execute: (query: unknown) => Promise<unknown> };
   };
-  const tx = adapter.sessions?.[txID]?.db ?? adapter.drizzle;
+  const tx = adapter.sessions?.[txID]?.db;
+  if (!tx) throw new Error("Booking transaction not found");
 
   await tx.execute(sql`SELECT pg_advisory_xact_lock(hashtext(${dateKey}))`);
 }