Without intervention, an agent begins forgetting at the instant the session ends. Every new conversation opens cold — a confident expert who has never seen this codebase. It re-derives. It re-asks. It re-fixes the bug you fixed in March. The cleverness is fully preserved; only the memory of having decided is lost.
In an untrained nervous system this is called the cold-start problem. A pianist without rehearsal must read every note. A mechanic without callus must measure every bolt. The remedy in flesh is well known: repetition cathects retention — a path traced enough times becomes the path of least resistance. The agent has no such path. Every session is the first session.
Vouch furnishes the path. It places, in the project itself, a small persistent organ that records what the agent has done and why — but only after a second pair of eyes signs the record. The cost is one extra step. The benefit is permanence.