Fix caching, Limits placement, and explain the board better

test/mainline-cards.test.ts

@@ -416,6 +416,46 @@ describe('card coverage', () => {
 // ---------------------------------------------------------------------------
 
 describe('the Limits sign moves with the Running Track (§2.1, Gap 4a)', () => {
+  it('refuses to build beyond the Limits sign', () => {
+    // §2.1 — the Running Track runs BETWEEN the Limits, so the sign is the only growth point.
+    // Offering the square PAST it produced, from one straight laid at (0,2):
+    //   limits · Whistle Post · limits · straight · limits
+    // — track on the far side of the sign, and a second sign planted beyond that.
+    const s = game();
+    const area = areaOf(s, 0);
+    s.turn.option = 'draw';
+
+    const beyondEast = { row: area.runningRow, col: area.limitsEast.col + 1 };
+    const beyondWest = { row: area.runningRow, col: area.limitsWest.col - 1 };
+    for (const placement of [beyondEast, beyondWest]) {
+      assert.notEqual(
+        check(s, 0, { type: 'track.lay', geometry: 'straight', hand: 'none', placement, variant: 0 }),
+        null,
+        `(${placement.row},${placement.col}) is outside the Limits and must not be placeable`,
+      );
+    }
+
+    // The sign itself IS legal — that is how the Running Track grows.
+    assert.equal(
+      check(s, 0, {
+        type: 'track.lay', geometry: 'straight', hand: 'none',
+        placement: { row: area.runningRow, col: area.limitsEast.col }, variant: 0,
+      }),
+      null,
+      'laying on the Limits sign must be how the track extends',
+    );
+
+    // The district hangs below the Running Track and is not bounded by the Limits at all.
+    assert.equal(
+      check(s, 0, {
+        type: 'track.lay', geometry: 'straight', hand: 'none',
+        placement: { row: area.runningRow - 1, col: 0 }, variant: 1,
+      }),
+      null,
+      'Secondary Track below the Office must stay legal',
+    );
+  });
+
   it('keeps the Limits at the ends, never stranded mid-track', () => {
     // Found by watching a replay: a district grew to
     //   (0,-5) (0,-4) (0,-3) (0,-2)=Power Plant [LIMITS] (0,0)=Office [LIMITS] (0,2) …