Rolling back an outer transaction leaves behind changes committed by an inner transaction. Repair the transaction handling so nested commits and rollbacks preserve the intended state.
Build the implementation in Java under /app, with /app/run.sh as its entry point. Read one JSON request from standard input and write one JSON result to standard output. Input is a list of begin, set (key and value), commit and rollback operations. State starts empty. Begin snapshots current state; commit discards only the latest snapshot; rollback restores it. Return final state. Missing transaction for commit/rollback, unknown operations or unclosed transactions must be rejected.
Reject inputs that violate an explicit validation rule with exit status 2, no standard output, and {"error":"invalid_input"} on standard error. For valid input, exit with status 0. Keep the implementation reusable for new inputs; it must work offline and must not depend on the example data being the only data it receives.
Repair or replace the unfinished /app/run.sh and add source files under /app. Malformed JSON must use the same invalid-input response. Do not read /tests or /oracle from the application.