Expand game engine, replay, tests, and documentation

src/engine/legal.ts

@@ -133,6 +133,10 @@ function newTrainCandidates(s: GameState): Intent[] {
     }
     out.push({ type: 'newTrain.passCar', trayId });
   }
+  const due = s.timetable[s.clock.stage - 1];
+  if (due !== null && due !== undefined) {
+    out.push({ type: 'newTrain.secondSection', trainNumber: due });
+  }
   return out;
 }
 
@@ -183,6 +187,8 @@ function placementCandidates(s: GameState, player: PlayerIndex): GridCoord[] {
       { row: row!, col: col! - 1 },
     ];
     for (const c of around) {
+      // Q7 — a district hangs BELOW the Running Track; there is nothing above it.
+      if (c.row > area.runningRow) continue;
       const k = `${c.row},${c.col}`;
       if (area.grid.has(k) || seen.has(k)) continue;
       seen.add(k);