Founder ruling. day is the source segment's day, or for an activity its start time. It is not the recording day, the last-seen day, or the ingest day. The only permitted fallback, for content that is genuinely not day-based, is the day it was last updated — and a fallback must be named as one rather than silently occupying the same field. Recorded because the field previously conflated recording, source and last-seen meanings, which the index research surfaced as an open question. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>