Linkage, Not Similarity
What long-term agent memory has to retrieve, and how it is measured
Vector similarity retrieves what sounds related; long-term memory has to retrieve what is connected. On LoCoMo a cosine index recovers every annotated turn for only 22.7% of multi-hop questions at k=20 while recovering at least one for 80.1% — the signature of a linkage failure that a better embedding does not fix. An index of atomic facts, each citing the turn it came from, plus two structural bonuses, raises complete evidence to 36.2% with nothing learned and under a millisecond per query. On MemoryAgentBench FactConsolidation the typed search scores 98.3 single-hop and 84.5 multi-hop pooled with no reader at all, against CAR's 94.8 / 51.5 with gpt-4o and Naive Brain's published 91 / 57 on a matched gpt-4o-mini backbone. Every figure carries a declared dev/test split, a frozen commit, bootstrap intervals, and its own chance floor; the ablations include two plausible additions that make the result worse.