Treat empty semantic cohorts as coverage gaps

When a dashboard combines current operational events with text-derived semantics, an empty recent text cohort should not produce rows of zero message activity. Hide those rows from the decision view, keep current operational metrics in their selected period, and, if useful, show the smallest historical cohort with usable text as a separately dated sample. Never blend the samples or reuse the older semantics as current-period counts. This prevents missing ingestion from masquerading as no human work while preserving a useful behavioral read.

Applies when: operational telemetry and message or transcript evidence have different coverage windows. Keywords: analytics coverage gaps empty cohort stale messages evidence windows