The Song, Not the Pin: Provenance-Conditioned Route Memory for Persistent Multi-Agent Navigation

Long-term memory matters when a stored record shapes a later action. In a multi-agent system, a semantically correct record may still refer to an ambiguous place, omit an executable path, be stale, or induce conflicting commitments. We study shared long-term memory at this action boundary. We model the transferable unit as an executable route with explicit provenance; a target record is its length-zero case. At materialization we freeze the share of foreign evidence supporting the commitment. Trust and age define a computable admissibility horizon, applied also to route edges, while decentralized reservation and rollback make action authority revocable. Controlled experiments in grids, VMAS, and a text world show that foreign memory has no single sign of effect. Under target scarcity, foreign commitments rarely complete directly but often transport agents into self-confirmation range; paired replay shows that sharing can either accelerate or degrade completion depending on coordination pressure. The analytically derived contract boundary matches all pre-specified target- and edge-validity hold-outs, verifying the specified memory contract rather than a universal forgetting law. Under a fixed local planner, route transfer preserves success beyond the first structural obstacle where endpoint-only transfer fails; a recipient-capability ladder shows that this gap is reconstructive cost, not an absolute information deficit. In a cross-session LLM check, structured foreign memory solves 10/10 tasks; raw transcript, rolling-summary, and lexical-retrieval memories reach at most 7/10, while a bare endpoint reaches 9/10 in the obstacle-free setting. In the evaluated settings, shared long-term memory is incomplete as retrievable content alone: action additionally depends on referential identity, sufficient execution structure, explicit provenance, time-bounded validity, and revocable coordination authority.