fix: improve road pathfinding junction quality in Mini Motorways

- Add stop-at-road mode to A*: snap to nearest road cell on approach
  instead of routing along the road to the cursor, producing clean T-
  and L-junctions without diagonal shortcuts from unexpected angles
- Tighten diagonal suppression rule: block diagonals when EITHER
  orthogonal intermediary is a road (previously required BOTH),
  preventing spurious diagonal shortcuts at T-junctions that would
  cause perpendicular approaches to fan out to three connections
- Refactor A* path reconstruction into shared helper and add early
  termination to avoid post-search state scanning

public/src/games/minimotorways/MiniMotorwaysGame.js

@@ -890,21 +890,27 @@ export default class MiniMotorwaysGame extends Phaser.Scene {
     const isPassable = (k) => sim.roads.has(k)
       || (sim.terrain[k] === TERRAIN.LAND && !sim.occupiedAt(k));
 
-    // State = cell * 9 + dirIndex (0-7 = one of DIRS, 8 = "no prior direction")
+    // State = cell * 9 + dirIndex (0-7 = DIRS entry, 8 = "no prior direction").
-    // Primary cost: new road tiles placed (integer).
+    // Primary cost: new road tiles. Tiebreaker: tiny turn penalty so straight
-    // Tiebreaker: tiny penalty per direction change so straight/diagonal runs win.
+    // and diagonal runs beat zigzags when tile counts are equal.
     const ND = 9;
-    const TURN_COST = 0.001; // << 1, so never overrides tile-count optimality
+    const TURN_COST = 0.001;
     const stateCount = WORLD_W * WORLD_H * ND;
     const dist = new Float64Array(stateCount).fill(Infinity);
     const par = new Int32Array(stateCount).fill(-1);
+    const settled = new Uint8Array(stateCount);
+
+    // When the cursor is on an existing road and we're not starting from one,
+    // treat ANY road cell as the goal instead of routing along the road to the
+    // cursor. The nearest road cell on a straight/diagonal approach always wins
+    // (0 turns), so you get a clean T- or L-junction rather than a diagonal
+    // shortcut that sneaks up to the road from an unexpected angle.
+    const stopAtRoad = sim.roads.has(to) && !sim.roads.has(from);
 
     const startState = from * ND + 8;
     dist[startState] = 0;
 
-    const settled = new Uint8Array(stateCount);
     const heap = [startState];
-
     const swap = (a, b) => { const t = heap[a]; heap[a] = heap[b]; heap[b] = t; };
     const siftUp = (i) => {
       while (i > 0) {
@@ -927,11 +933,15 @@ export default class MiniMotorwaysGame extends Phaser.Scene {
     const heapPop = () => {
       const top = heap[0];
       const last = heap.pop();
-      // Only replace root if heap still has elements — avoids the single-element
-      // infinite loop where heap.pop() empties the array then heap[0]=last refills it.
       if (heap.length > 0) { heap[0] = last; siftDown(0); }
       return top;
     };
+    const reconstruct = (state) => {
+      const path = [];
+      let s = state;
+      while (s !== -1) { path.unshift((s / ND) | 0); s = par[s]; }
+      return path;
+    };
 
     while (heap.length > 0) {
       const state = heapPop();
@@ -939,10 +949,16 @@ export default class MiniMotorwaysGame extends Phaser.Scene {
       settled[state] = 1;
 
       const cur = (state / ND) | 0;
-      const curDir = state % ND;
-      const cd = dist[state];
 
+      // Terminate: reached specific target, or (in road-stop mode) any road cell.
+      if (cur !== from && (cur === to || (stopAtRoad && sim.roads.has(cur)))) {
+        return reconstruct(state);
+      }
+
+      const cd = dist[state];
+      const curDir = state % ND;
       const cx = xOf(cur); const cy = yOf(cur);
+
       for (let di = 0; di < 8; di++) {
         const [dx, dy] = DIRS[di];
         const nx = cx + dx; const ny = cy + dy;
@@ -962,18 +978,7 @@ export default class MiniMotorwaysGame extends Phaser.Scene {
       }
     }
 
-    // Find the cheapest arrival direction at the destination.
+    return null; // target unreachable
-    let bestState = -1; let bestDist = Infinity;
-    for (let di = 0; di < ND; di++) {
-      const s = to * ND + di;
-      if (dist[s] < bestDist) { bestDist = dist[s]; bestState = s; }
-    }
-    if (bestState === -1 || bestDist === Infinity) return null;
-
-    const path = [];
-    let s = bestState;
-    while (s !== -1) { path.unshift((s / ND) | 0); s = par[s]; }
-    return path;
   }
 
   buildDrawPath() {

public/src/games/minimotorways/MiniMotorwaysLogic.js

@@ -383,12 +383,15 @@ export class Sim {
       const nk = keyOf(nx, ny);
       if (!this.roads.has(nk)) continue;
       if (dx !== 0 && dy !== 0) {
-        // Crossing rule: if both shared corners carry road, the two diagonals
+        // Suppress diagonal if either orthogonal intermediary is a road: either
-        // of this 2x2 block would cross — and the corners already connect the
+        // the X-crossing case (both corners are roads, two diagonals would
-        // cells orthogonally — so the diagonal edge is suppressed.
+        // cross) or the T-junction case (one corner is road — traffic already
+        // flows through that cell, so the diagonal shortcut is spurious and
+        // would make a perpendicular approach fan out to three connections
+        // instead of one clean junction).
         const cornerA = keyOf(x + dx, y);
         const cornerB = keyOf(x, y + dy);
-        if (this.roads.has(cornerA) && this.roads.has(cornerB)) continue;
+        if (this.roads.has(cornerA) || this.roads.has(cornerB)) continue;
       }
       out.push({ k: nk, cost: dx !== 0 && dy !== 0 ? SQRT2 : 1 });
     }