Make S/R matrix runner cross-platform

docs/research/sr-levels-and-exits.md

@@ -412,10 +412,22 @@ Detector evidence (`sources`, rejection count, last rejection age) stays in the
 pure backtest objects. It is deliberately not migrated into the production DB
 schema until a variant passes validation.
 
-Run the training matrix with `--entry-end 2024-06-30 --sr-audit`, choose one arm,
-and record that lock before running exactly control and the locked arm with
-`--entry-start 2024-07-01`. Use `scripts/compare_sr_variants.py` to produce the
-paired cohort CSV and summary JSON.
+The cross-platform matrix runner is only an orchestrator around the existing
+`run_backtest_snapshot.py`; it contains no duplicate backtest logic. On macOS:
+
+```bash
+.venv/bin/python scripts/run_sr_v2_matrix.py train --workers 14
+```
+
+Choose one arm and record that lock before running exactly control and that arm:
+
+```bash
+.venv/bin/python scripts/run_sr_v2_matrix.py validate \
+  --locked-arm confirmed_rounds --workers 14
+```
+
+Replace `confirmed_rounds` with the recorded winner. The validation command also
+calls `scripts/compare_sr_variants.py` to produce the paired cohort CSV and JSON.
 
 The post-2024 interval has informed earlier research, so this is validation rather
 than a pristine holdout; do not sweep variants on it. No deployment follows