Roll Back the Whole Attempt

The missing-member call now has a named failure: sqlite3.IntegrityError. Its earlier insert is still pending, so the function needs to make an explicit failure decision.

Open transactions.py. Wrap the two inserts, commit, and successful return in one try block. Then add this narrow handler:

except sqlite3.IntegrityError:
    connection.rollback()
    return False

rollback() discards changes that are still pending on this connection. It does not delete old committed loans. Here, it removes loan 7101, the valid prefix of the failed pair.

Keep connection.commit() after both inserts in the successful branch. The complete behavior is now:

Press Run. The valid block should still reopen with IDs [7001, 7002]. The missing-member block should now report False, no escaping database-rule error, and empty proposed IDs on both connections.

The handler catches only sqlite3.IntegrityError. Do not catch Exception or all sqlite3.Error values. If a different defect appears, such as invalid SQL or an unusable Python argument, returning False would make it look like the known catalog outcome. That unrelated failure should remain visible.

Submit places the bad row first in one case and second in another. It also starts with unrelated committed rows and verifies they remain. A rollback should resolve this attempted pair, not clear the table. Finally, it runs a harmless query through the supplied connection, because resolving the transaction does not transfer ownership of the connection to this function.

This manual branch is correct and worth seeing once. You can keep the same results while letting the connection manage its normal commit and rollback decisions.