The capability that lets each new decision session reason in light of every prior one — the calls already made, the reasoning behind them, the constraints declared, and the outcomes recorded. Ordinary chat memory is per-conversation and retrieval-shaped; cross-session memory is decision-aware, meaning it carries structured claims and commitments rather than raw transcript.
The practical difference shows up in contradiction detection: a system with cross-session memory can tell you that the plan on the table conflicts with a decision you made two months ago, which no amount of context-window stuffing reliably produces.