# Detection and Repair of Derived Memory

Values an AI assistant derives from a person's records, such as important contacts, can go stale when an input changes. MemShift uses synthetic worlds that fork only on one kind of change to score whether a memory noticed the change and whether its repair was right, against gold fixed before any text and without an LLM judge. Across four open-weight models, detection helps only as much as repair allows: after a redefinition, the key-by-exact-recomputation interaction is +38.8 percentage points.

Values an AI assistant derives from a person's records, such as important contacts, can go stale when an input changes. MemShift uses synthetic worlds that fork only on one kind of change to score whether a memory noticed the change and whether its repair was right, against gold fixed before any text and without an LLM judge. Across four open-weight models, detection helps only as much as repair allows: after a redefinition, the key-by-exact-recomputation interaction is +38.8 percentage points.