Module liveness 

Event-driven liveness: has a triggering change landed since a check last ran? Impure (shells git), mirroring staleness.rs. The verdict engine stays pure — this produces a bool the caller passes into verdict_for.

Functions

changed_since

True if any commit reachable from HEAD and NEWER than since_commit touches one of paths (a triggered_by set). None if git fails or since_commit is unknown — in which case event-driven staleness is simply NOT evaluated (never a false not-green).