A compression_analytics row was written only on a net-positive saving
(chatCore: result.compressed || fallbackApplied || cavemanOutputModeApplied).
A Stacked RTK->Caveman pipeline that ran on already-compact context saved
nothing -> no row -> indistinguishable from 'never dispatched'
(byMode.stacked.count stayed flat while Ultra climbed).
Attempted-but-no-op runs are now recorded via writeCompressionSkip with a
skip_reason. A new skip_reason column (added through the existing
ensureCompressionAnalyticsColumns ALTER path) marks these rows; the analytics
summary excludes them from every saving aggregate (via a single successWhere =
'skip_reason IS NULL' filter, so historical totals/averages are byte-identical)
and surfaces them as per-mode 'skipped' plus totalSkipped / bySkipReason. The
Mode Breakdown shows 'N skipped (no-op)'.
TDD: compressionAnalytics.test.ts gains coverage that skip rows are counted
separately without polluting saving aggregates, and that a skip-only mode still
appears (count 0, skipped > 0). Fail-before proven by reverting the successWhere
exclusion (both new tests fail). typecheck:core + eslint clean; 17/17 suite green.
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