docs(cursor): explain attachment ownership and caller coordination

README.md

@@ -250,6 +250,15 @@ an execution, and does not extend server result retention. It raises the same
 missing/cancelled execution errors described above. A second cursor cannot
 attach an execution already tracked by that connection.
 
+On SQL sessions that support attachment, attaching a running execution
+transfers event delivery to the new connection, even if the previous
+connection remains open. The duplicate guard
+only covers cursors on one connection. Another connection can attach again and
+take event delivery back. The previous connection can also still cancel the
+execution, including through cursor close or reuse. Callers must coordinate the
+handoff so stale workers cannot reattach or cancel it; attach provides no
+cross-connection lock or ownership fencing.
+
 ### Stopping the SQL session
 
 Closing a connection leaves its SQL session running until

wherobots/db/cursor.py

@@ -200,6 +200,8 @@ def attach(self, execution_id: str, store: Store | None = None) -> None:
         Connect to the original SQL session first. Pass the original Store for
         stored results. This never submits SQL or extends server result retention;
         a missing execution raises ExecutionNotFoundError when fetching.
+        On SQL sessions that support attachment, this transfers event ownership.
+        It does not fence other connections; callers must coordinate the handoff.
         """
         if not isinstance(execution_id, str) or not execution_id.strip():
             raise ProgrammingError("execution_id must be a non-empty string")