fix(workbench): serialize events and target work order sync

app/infra/db/postgresql/workbench_events.py

@@ -1,7 +1,31 @@
 """Cursor reads for the durable project-scoped workbench event log."""
 from __future__ import annotations
 
-from psycopg import AsyncConnection
+from psycopg import AsyncConnection, Connection
+
+
+EVENT_ORDER_LOCK = "tjwater-workbench:event-order"
+
+
+async def lock_event_transaction(connection: AsyncConnection) -> None:
+    """Serialize v2 event-producing transactions before business locks/writes.
+
+    PostgreSQL sequence allocation is not commit order. All producers must use
+    this same transaction lock so a committed higher cursor cannot hide an
+    earlier, still-uncommitted event. Other BizDBs remain rollout opt-out.
+    """
+    if getattr(getattr(connection, "info", None), "dbname", None) == "tjwater_v2":
+        await connection.execute(
+            "SELECT pg_advisory_xact_lock(hashtextextended(%s,0))", (EVENT_ORDER_LOCK,)
+        )
+
+
+def lock_event_transaction_sync(connection: Connection) -> None:
+    """Synchronous counterpart using the identical PostgreSQL lock key."""
+    if getattr(getattr(connection, "info", None), "dbname", None) == "tjwater_v2":
+        connection.execute(
+            "SELECT pg_advisory_xact_lock(hashtextextended(%s,0))", (EVENT_ORDER_LOCK,)
+        )
 
 
 class WorkbenchEventRepository: