Implement nose coupling so run-arounds work, and stop coupling wiping the district

src/engine/events.ts

@@ -22,7 +22,19 @@ export type GameEvent =
   // -- local operations
   | { type: 'localOpsOptionChosen'; player: PlayerIndex; option: LocalOpsOption }
   | { type: 'trayMoved'; trayId: TrayId; from: GridCoord; to: GridCoord; movesRemaining: number; facing?: 'n' | 's' | 'e' | 'w' }
-  | { type: 'carsCoupled'; trayId: TrayId; at: GridCoord; stock: RollingStock[] }
+  | {
+      type: 'carsCoupled';
+      trayId: TrayId;
+      at: GridCoord;
+      stock: RollingStock[];
+      /** The cards the cars were lifted from — the ones the crew actually ran over. */
+      from: GridCoord[];
+      /**
+       * Coupled onto the ENGINE'S NOSE rather than behind the train (§A.3). True when the crew was
+       * running forward: the engine meets the cars head-on and takes them on the front.
+       */
+      toNose: boolean;
+    }
   | { type: 'carsDropped'; trayId: TrayId; at: GridCoord; stock: RollingStock[] }
   | { type: 'consistSorted'; trayId: TrayId; at: GridCoord; before: RollingStock[]; after: RollingStock[] }
   | { type: 'cardDrawn'; player: PlayerIndex; source: 'homeOffice' | 'department'; slot?: number; cardId: CardId }