Bounded individual TWT responder checkpoint on ns-3.48 Local acceptance: 245 test cases, both physical probes and ten native-resolution mapper processes passed. 50 new responder cases cover bounded retention, conflicting tokens, capacity, response and ACK loss recovery, owned queues and lifecycle cleanup. Scope: immutable AP response or silence retention and exact duplicate replay on one associated QoS HE link, with fixed expiry, bounded capacity and version-owned response cleanup; prior explicit clock mapping and paired executor APIs remain available. No autonomous requester retry, delayed AP response, admission, negotiated executor installation/removal or automatic TSF synchronization is added. Protected/broadcast TWT, MLO/EMLSR, OFDMA, full-frame containment and energy validation remain unsupported. Finite retention cannot exclude arbitrarily late identical input; in-flight exchanges may finish after removal. The earlier MLO regression remains unresolved; see doc/twt/REGRESSION_STATUS.md.