When External Memory Becomes Agent State: Recorded Lineage and Controlled Reuse in LLM Agents

Persistent-memory agents can rewrite external records into their own long-term state. A terminal success rate does not reveal whether an external record was merely shown, used in a decision, copied into a new record, inherited by later writes, or used again. We study recorded lineage: a committed record is linked to an external seed only through parent identifiers declared by the model and validated by the evaluator. We analyze this operational relation separately from content correctness, retrieval, and outcomes. Across three deterministic studies, ordinary writeback created 48 seed-descended records; disabling all writeback created none but reduced task success from 5/10 to 0/10. Two selective policies then blocked all recorded descendants. Lineage-selective admission nevertheless committed 36 DeepSeek and 3 Kimi writes without recorded seed ancestry, whereas exposure-triggered admission committed none. On the original task horizon, the prespecified operational comparison was near floor and did not favor lineage selection. Finally, when a retained notice-derived record was scheduled for later use, lineage selection achieved 67/120 versus 1/120 successes on DeepSeek and 72/120 versus 6/120 on Kimi. Scrambling only the record’s task-relevant content reduced success to 4/120 and 9/120. Together, the studies separate lineage formation, write-policy selectivity, and consequence after scheduled reuse. Code and anonymized data are available in an anonymous artifact.