created harness to better test bots. improved bot play

src/engine/apply.ts

@@ -229,11 +229,23 @@ export function canBoard(s: GameState, player: PlayerIndex, at: GridCoord): bool
   return trainAtOfficeWith(s, player, (c) => c.type === 'coach' && !c.loaded);
 }
 
-/** §9.2 — de-training needs an open red slot and a train carrying a loaded coach. */
+/**
+ * §9.2 — de-training needs an open red slot, a train carrying a loaded coach, AND AN EMPTY COACH IN
+ * THE DIVISION YARD.
+ *
+ * "*Requirements: a white empty coach in the Division Yard and an unoccupied red Unloading slot.
+ * Replace the blue coach on the train with the white one.*" The empty coach is where the passengers
+ * were sitting — it has to come from somewhere, and the rule says where.
+ *
+ * That requirement was missing, and the reducer conjured the coach rather than taking it, so every
+ * de-training MINTED a coach: the loaded one went to the red box and a new empty one appeared in the
+ * train. Measured at 1.29 cars a game created out of nothing across the two inbound paths.
+ */
 export function canDetrain(s: GameState, player: PlayerIndex, at: GridCoord): boolean {
   const f = facilityAt(s, player, at);
   if (!f || f.kind !== 'passenger' || portersLeft(f) < 1) return false;
   if (f.inboundBox.length >= f.capacity.inbound) return false;
+  if (!s.yards.divisionYard.some((c) => c.type === 'coach' && !c.loaded)) return false;
   return trainAtOfficeWith(s, player, (c) => c.type === 'coach' && c.loaded);
 }
 
@@ -557,6 +569,14 @@ export function check(s: GameState, player: PlayerIndex, i: Intent): RejectionCo
       if (laborersLeft(f) < 1) return 'RESOURCE_SPENT';
       const car = f.industryTrack.cars[i.carIndex];
       if (!car || !car.loaded) return 'WRONG_CAR_TYPE';
+      /**
+       * §9.3 — "*Requirements: a load on the industry's track AND AN EMPTY CAR OF THAT TYPE IN THE
+       * DIVISION YARD. The first Laborer replaces the load with an empty car of that type.*"
+       *
+       * The empty car requirement was not checked and the reducer conjured the car rather than
+       * taking it, so every unload minted one. Unloading is meant to consume supply.
+       */
+      if (!s.yards.divisionYard.some((c) => c.type === car.type && !c.loaded)) return 'NO_SUITABLE_CAR';
       // The load is placed on WORK, the last box, so that box must be free.
       return f.menAtWork[f.menAtWork.length - 1] === null ? null : 'BOX_FULL';
     }
@@ -1399,8 +1419,13 @@ export function reduce(s: GameState, e: GameEvent): void {
         const tray = s.trays.get(id);
         const ci = tray?.consist.findIndex((c) => c.type === 'coach' && c.loaded) ?? -1;
         if (tray && ci >= 0) {
+          // The empty coach comes OUT OF THE DIVISION YARD, as §9.2 says. It used to be conjured,
+          // which minted a coach on every de-training.
+          const yi = s.yards.divisionYard.findIndex((c) => c.type === 'coach' && !c.loaded);
+          const empty = yi >= 0 ? s.yards.divisionYard.splice(yi, 1)[0]! : { type: 'coach' as const, loaded: false };
+          refillDivisionYardIfEmpty(s);
           f.inboundBox.push(tray.consist[ci]!);
-          tray.consist[ci] = { type: 'coach', loaded: false };
+          tray.consist[ci] = empty;
           break;
         }
       }
@@ -1448,7 +1473,14 @@ export function reduce(s: GameState, e: GameEvent): void {
     case 'unloadBegan': {
       const f = facilityAt(s, e.player, e.at)!;
       const ci = f.industryTrack.cars.findIndex((c) => c.loaded);
-      if (ci >= 0) f.industryTrack.cars[ci] = { type: e.carType, loaded: false };
+      if (ci >= 0) {
+        // §9.3 — the replacement empty comes out of the Division Yard. Conjuring it here is what
+        // minted a car on every unload, and it also skipped a requirement the rule states.
+        const yi = s.yards.divisionYard.findIndex((c) => c.type === e.carType && !c.loaded);
+        const empty = yi >= 0 ? s.yards.divisionYard.splice(yi, 1)[0]! : { type: e.carType, loaded: false };
+        refillDivisionYardIfEmpty(s);
+        f.industryTrack.cars[ci] = empty;
+      }
       f.menAtWork[f.menAtWork.length - 1] = { type: e.carType, dir: 'in' };
       f.usedThisStage.laborers += 1;
       break;