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

src/engine/advance.ts

@@ -30,6 +30,8 @@ import {
   collectiveRevenueFloor,
   lengthProfile,
   officeProfile,
+  REGIONS_PER_MAINLINE_CARD,
+  mainlineProfile,
 } from './content.ts';
 import type { Direction } from './content.ts';
 import type { GameEvent } from './events.ts';
@@ -186,7 +188,7 @@ function newTrainPhase(s: GameState, events: GameEvent[]): AdvanceResult {
         id: trayId,
         trainNumber: due,
         trainIsExtra: false,
-        engineFront: true,
+        engineAt: 0,
         consist: [],
         direction,
         position: { at: 'divisionPoint', side },
@@ -219,7 +221,7 @@ function newTrainPhase(s: GameState, events: GameEvent[]): AdvanceResult {
         id: trayId,
         trainNumber: number,
         trainIsExtra: false,
-        engineFront: true,
+        engineAt: 0,
         consist: [],
         direction,
         position: { at: 'divisionPoint', side },
@@ -250,7 +252,7 @@ function newTrainPhase(s: GameState, events: GameEvent[]): AdvanceResult {
       id: trayId,
       trainNumber: number,
       trainIsExtra: true,
-      engineFront: true,
+      engineAt: 0,
       consist: [],
       direction: 'east',
       position: { at: 'divisionPoint', side: 'west' },
@@ -488,6 +490,53 @@ function moveTrain(
     // Q1/Q2 — crossing takes a whole number of Stages set by the card's speed and the train's
     // Fast/Slow class. Count it down rather than stepping through printed cells.
     if (transit.stagesRemaining > 1) {
+      /**
+       * Q13 — REAR-END COLLISIONS, answered: a train collides when it CATCHES UP.
+       *
+       * §10 makes a Mainline collision the Superintendent's fault and removes both trains, and ABS
+       * Signals exists to stop trains rear-ending each other — but §8.3's trigger list never named
+       * one and none was implemented, so granting clearance was free: both trains survived, no
+       * penalty, and ABS Signals protected against nothing.
+       *
+       * Colliding on CATCHING UP is the version that rewards judging the gap. A following train
+       * that closes on the one ahead runs into it; a following train that never closes is fine, so
+       * clearance becomes a bet on relative speed rather than a formality. §2.1 divides the card
+       * into two regions, and sharing one is what "caught up" means.
+       *
+       * ABS Signals does what it says instead: the follower stops SHORT of the collision and holds.
+       */
+      const regionOf = (t: { stagesTotal: number; stagesRemaining: number }): number => {
+        const entry = REGIONS_PER_MAINLINE_CARD - t.stagesTotal;
+        const elapsed = t.stagesTotal - t.stagesRemaining;
+        return Math.min(REGIONS_PER_MAINLINE_CARD - 1, Math.max(0, entry + elapsed));
+      };
+      // NOT on a card that prints "trains may pass". Double Track and Uncontrolled Siding hold two
+      // trains because they HAVE two roads, so a train catching another there goes past it — that
+      // is what the card is for. Without this the mechanic fired 0.41 times a game while the bot
+      // never once granted clearance, which is the tell: those were all passing cards.
+      const mayPass = mainlineProfile(node.card).trainsMayPass;
+      const next = regionOf({ stagesTotal: transit.stagesTotal, stagesRemaining: transit.stagesRemaining - 1 });
+      const ahead = mayPass
+        ? undefined
+        : node.transits.find(
+            (t) => t.tray !== id && t.direction === transit.direction && regionOf(t) === next,
+          );
+
+      if (ahead) {
+        if (node.absSignals) {
+          // "Trains on this card will not rear-end each other; they stop short of a collision."
+          events.push({
+            type: 'trainHeld',
+            trainNumber: tray.trainNumber ?? 0,
+            reason: 'ABS Signals — held short of the train ahead',
+          });
+          return 'held';
+        }
+        // §10 — the Superintendent let it in behind the other, so it is the Superintendent's fault.
+        collide(s, s.clock.superintendent, [id, ahead.tray], events, 'ran into the train ahead', 'the Mainline');
+        return 'moved';
+      }
+
       transit.stagesRemaining -= 1;
       return 'moved';
     }
@@ -756,25 +805,6 @@ function shiftChange(s: GameState, events: GameEvent[]): AdvanceResult {
     // Telegraph/Telephone/Radio are each usable once a Day.
     for (const area of s.officeAreas.values()) area.dispatchUsedToday = [];
 
-    /**
-     * THE CLASSIFICATION YARD GOES BACK INTO SERVICE OVERNIGHT.
-     *
-     * ASSUMPTION, flagged rather than derived: Gap 2c says engines and cabooses return to the
-     * Division Yard and everything else to Classification, and the recovered rules never say how
-     * Classification empties. It was write-only — seven places pushed into it and nothing ever read
-     * it — so rolling stock drained one way and left the game. Measured at 30 cars a game dead by
-     * the end, 37% of the 80 dealt at setup.
-     *
-     * Sorting cars for redistribution is what a classification yard is FOR, and a Day is its
-     * natural cycle, so they return at the Day boundary. This does not bind a 5-Day game — the
-     * Division Yard still held 16.6 loaded freight cars at the end and ran dry in 2 games of 100 —
-     * but a campaign-length game would have starved.
-     */
-    if (s.yards.classificationYard.length > 0) {
-      s.yards.divisionYard.push(...s.yards.classificationYard);
-      s.yards.classificationYard = [];
-    }
-
     s.clock.day += 1;
     s.clock.stage = 1;
     s.collisionsToday = 0;