lastTouched

The later of contentRevised and metadataRevised — "last touched of any kind". Materialised (not derived at query time) so "revised" filtering and ordering push into the database against a single indexable column, matching the in-memory backend's Proposition.lastTouched semantics. Written on every save; the partial-update writers (decay sweep, re-embed) don't touch the revision clocks, so it never drifts. On a node written before this column existed it falls back to the later of the two revision clocks.