added harness to support bots being able to run / test strategies.

TODO.md

@@ -66,12 +66,17 @@ Ordered within each section by how much it is currently costing us.
       Revisit when setup gains an interactive phase; the orientation matters, because it decides
       which direction climbs and therefore what Brakeman and Helpers are worth.
 
-- [ ] **Measure with error bars from now on.** Revenue has a standard deviation of ~9, so a
-      100-game run carries about ±1.0 of noise — every single-change revenue claim in the changelog
-      before the Interlocking work is inside that. Use paired per-seed comparison (the harness deals
-      the same seeds either way) and 400+ games before calling a heuristic change good or bad. The
-      first attempt at the Running Track straight was read as a 0.6 REGRESSION on 100 games and is
-      a 0.7 improvement on 400.
+- [x] ~~**Measure with error bars from now on.**~~ Built: `node src/sim/compare.ts 1600 <tweak>=<n>`
+      runs the current bot and one variant over the same deals and reports the paired difference.
+      Pairing drops σ from ~9 on the level to **5.3 on the difference**, so 1600 seeds gives ±0.13 in
+      about 1m45s — the noise floor is now ~±0.15 rather than ±1.0. Threshold to keep a heuristic is
+      **t ≥ 3**, and the report prints the better/worse/identical split beside the mean, because a
+      mean carried by a skewed tail is a different claim from broad improvement.
+- [ ] **Re-run the three "worth ~0" action-mix experiments against the new floor.** Capping the draw,
+      pairing the two halves of a load, and restricting Enhancements were each measured "within noise
+      of zero" over 400 games — but at 400 games the standard error is ±0.33, so a real +0.5 would
+      have looked like nothing. They are nearly free to re-run now and at least one may have been
+      discarded wrongly.
 - [x] ~~**Confirm the Classification Yard rule against the source.**~~ Confirmed, and the guess was
       wrong. The rule is: used Rolling Stock to the Classification Yard, used engines and cabooses
       straight back to the Division Yard, and the Classification Yard empties ONLY when the Division