Restore cross-platform verification coverage

Use a native absolute path in the SMART override test so Windows verifies the same contract as Unix. Move the metrics concurrency proof into the canonical verification artifact and document that live ingestion remains independent from lifecycle maintenance.

docs/release-control/v6/internal/subsystems/performance-and-scalability.md

@@ -1229,7 +1229,14 @@ aggregate-only min/max columns stay unset. Rollups must not be hard-coded to a
 5-minute disk-write cadence: the default cadence should favor set-based
 transactions, remain bounded by raw retention so data is aggregated before
 pruning, and stay overrideable for operators who deliberately trade freshness
-for lower write frequency. Rollup transactions must also keep a bounded
+for lower write frequency. Startup cleanup, rollup, and retention must run on a
+lifecycle-owned maintenance worker separate from the worker draining the
+bounded live-ingestion queue. SQLite remains the serialization boundary for
+their transactions, but maintenance CPU or read work must not stop buffered
+writes or `Flush` barriers from progressing; shutdown must join both workers
+before closing their shared database. `pkg/metrics/store_additional_test.go`
+must prove ingestion remains live while startup maintenance is blocked. Rollup
+transactions must also keep a bounded
 time-window working set and resume from checkpoints across invocations instead
 of aggregating every pending series and bucket in one global SQLite GROUP BY
 that can spike RSS on agent-heavy installs. The runtime must also allow an explicit