CheckinBaseline and the extras-family config read each paid a full frame-header scan per invocation (#120). A shared openLogAdoptingIndex adopts the .zit-cache sidecar (#112's pattern), refreshing on miss; extras' path is read-only per B-extras-16. tk single-file diff: 0.220s -> 0.020s. check-in: be281ab760 user: dmestas tags: trunk