Persistent memory lets language model agents reuse information across sessions, but it also makes errors durable: a poisoned, stale, or misattributed record can alter reasoning, tool use, answers, and subsequent memory writes. Existing defenses mainly detect or delete suspicious memories, or revise the current response. Deleting the source leaves already propagated claims, actions, and derived memories active, whereas resetting the store or replaying the full trace destroys benign state and repeats unnecessary computation. We therefore formulate post-failure memory recovery: given a failed execution and diagnosed faulty memories, regenerate the answer and clean up affected persistent state while retaining unaffected work. Our dependency-guided rollback repair builds a typed memory-to-action graph from runtime provenance, traces explicit downstream dependencies, preserves candidates with independent trusted support, deactivates unsupported memory state, and selectively replays only answer-relevant affected computation. We evaluate this approach on a 150-case controlled benchmark spanning three tool-use domains and four memory failure types, and on a 50-case trajectory-derived stress test adapted from LongMemEval-V2. On the controlled benchmark, it achieves 85.3% immediate recovery versus 77.3% for LLM-judge repair, the strongest baseline, while preserving all benign memories and using 41.8% fewer LLM calls. Selective replay, however, leaves higher recurrence than LLM-judge repair (26.6% vs. 12.1%), exposing a trade-off between targeted repair and broader recomputation. On the adapted subset, it reaches 68.0% recovery versus 54.0% for the next best method, with 5.9% recurrence. Code and data are available at https://github.com/xiaoqi-7/memory-rollback.

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