Wrap torus neighbor steps with modulo

gameblocks/modules/behavior/GridPathPlanner.js

@@ -27,6 +27,13 @@ function wrapDelta(delta, size) {
   return Math.min(Math.abs(delta), size - Math.abs(delta));
 }
 
+function wrapCoord(value, size) {
+  if (!Number.isFinite(size) || size <= 0) return 0;
+  let wrapped = value % size;
+  if (wrapped < 0) wrapped += size;
+  return wrapped;
+}
+
 function priorityInsert(open, entry) {
   let index = open.length;
   while (index > 0 && open[index - 1].f > entry.f) {
@@ -43,10 +50,8 @@ function stepCell(cell, direction, board, wrap, navigation) {
   };
 
   if (wrap) {
-    if (next.right < 0) next.right = board.columns - 1;
-    if (next.right >= board.columns) next.right = 0;
-    if (next.forward < 0) next.forward = board.rows - 1;
-    if (next.forward >= board.rows) next.forward = 0;
+    next.right = wrapCoord(next.right, board.columns);
+    next.forward = wrapCoord(next.forward, board.rows);
     return next;
   }
 

gameblocks/modules/behavior/GridPathPlanner.wrap-neighbors.test.js

@@ -0,0 +1,33 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { GridPathPlanner } from './GridPathPlanner.js';
+
+const navigation = {
+  vectors: {
+    north: { right: 0, forward: 1 },
+    east: { right: 1, forward: 0 },
+    south: { right: 0, forward: -1 },
+    west: { right: -1, forward: 0 },
+  },
+  neighborOrder: ['north', 'east', 'south', 'west'],
+};
+
+test('wrap neighbors from the origin use torus edges, not clamp', () => {
+  const planner = new GridPathPlanner({ navigation, columns: 10, rows: 10, wrap: true });
+  const neighbors = Object.fromEntries(
+    planner.getNeighbors({ right: 0, forward: 0 }).map((entry) => [entry.direction, entry.cell])
+  );
+  assert.deepEqual(neighbors.west, { right: 9, forward: 0 });
+  assert.deepEqual(neighbors.south, { right: 0, forward: 9 });
+  assert.deepEqual(neighbors.east, { right: 1, forward: 0 });
+});
+
+test('wrap neighbors from far out-of-board cells use modulo, not the far edge', () => {
+  const planner = new GridPathPlanner({ navigation, columns: 10, rows: 10, wrap: true });
+  const neighbors = Object.fromEntries(
+    planner.getNeighbors({ right: -5, forward: 0 }).map((entry) => [entry.direction, entry.cell])
+  );
+  // -5 + 1 = -4 → 6 on a period-10 torus. Clamp-to-edge would have produced 9.
+  assert.deepEqual(neighbors.east, { right: 6, forward: 0 });
+  assert.deepEqual(neighbors.west, { right: 4, forward: 0 });
+});