adding classification and division yard updates, train collisions, engine and car updates, turnout improvements.

src/engine/apply.ts

@@ -1174,6 +1174,7 @@ export function reduce(s: GameState, e: GameEvent): void {
         (c) => c.type === e.stock.type && c.loaded === e.stock.loaded,
       );
       if (idx >= 0) s.yards.divisionYard.splice(idx, 1);
+      refillDivisionYardIfEmpty(s);
       f.outboundBox.push(e.stock);
       s.turn.freightAgentUsed = true;
       break;
@@ -1236,6 +1237,7 @@ export function reduce(s: GameState, e: GameEvent): void {
         (c) => c.type === e.stock.type && c.loaded === e.stock.loaded,
       );
       if (idx >= 0) s.yards.divisionYard.splice(idx, 1);
+      refillDivisionYardIfEmpty(s);
       tray.consist.push(e.stock);
       break;
     }
@@ -1674,6 +1676,30 @@ export function acceptsCar(tray: CrewTray, carType: CarType): boolean {
   return true;
 }
 
+/**
+ * §2 — WHEN THE DIVISION YARD RUNS OUT, THE CLASSIFICATION YARD GOES BACK INTO SERVICE.
+ *
+ * Used Rolling Stock is set out in the Classification Yard; used engines and cabooses go straight
+ * back to the Division Yard. The Classification Yard empties only when the Division Yard is bare —
+ * every car of every kind gone — and then all of it returns at once.
+ *
+ * Confirmed from the source after an earlier guess. The first implementation returned cars at the
+ * DAY boundary, which is a different rule and a much more generous one: it kept the yard topped up
+ * continuously, where this lets it run down to nothing and refill in one go. That difference is the
+ * whole of the supply pressure the game is meant to have.
+ *
+ * Called wherever a car leaves the Division Yard, so the refill happens the moment it empties
+ * rather than at the next convenient tick.
+ */
+export function refillDivisionYardIfEmpty(s: GameState): { type: 'yardRefilled'; count: number } | null {
+  if (s.yards.divisionYard.length > 0) return null;
+  if (s.yards.classificationYard.length === 0) return null;
+  const count = s.yards.classificationYard.length;
+  s.yards.divisionYard.push(...s.yards.classificationYard);
+  s.yards.classificationYard = [];
+  return { type: 'yardRefilled', count };
+}
+
 /** A fresh Limits sign. The set is "2N + spares" (§12), so relocating one is not a supply question. */
 function limitsCard(): TrackCard {
   return {