feat: add findNearestWalkable method to GameMap

Adds a method that searches outward from a center position in Manhattan
distance rings to find the nearest walkable tile within a given radius.
Returns null if no walkable tile is found. Includes 5 tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/map/GameMap.ts

@@ -45,6 +45,25 @@ export class GameMap {
     });
   }
 
+  findNearestWalkable(centerX: number, centerY: number, radius: number): Position | null {
+    if (this.isWalkable(centerX, centerY)) {
+      return { x: centerX, y: centerY };
+    }
+    for (let dist = 1; dist <= radius; dist++) {
+      for (let dx = -dist; dx <= dist; dx++) {
+        const dyRange = dist - Math.abs(dx);
+        for (const dy of [-dyRange, dyRange]) {
+          const x = centerX + dx;
+          const y = centerY + dy;
+          if (this.isWalkable(x, y)) {
+            return { x, y };
+          }
+        }
+      }
+    }
+    return null;
+  }
+
   getRandomWalkable(): Position {
     let x: number, y: number;
     do {

server/src/map/__tests__/GameMap.test.ts

@@ -0,0 +1,49 @@
+import { describe, it, expect } from 'vitest';
+import { GameMap } from '../GameMap.js';
+
+describe('GameMap.findNearestWalkable', () => {
+  it('returns the exact tile if it is walkable', () => {
+    const map = new GameMap(10, 10);
+    const result = map.findNearestWalkable(5, 5, 3);
+    expect(result).toEqual({ x: 5, y: 5 });
+  });
+
+  it('returns a nearby walkable tile if center is obstacle', () => {
+    const map = new GameMap(10, 10);
+    map.setObstacle(5, 5);
+    const result = map.findNearestWalkable(5, 5, 3);
+    expect(result).not.toBeNull();
+    const dx = Math.abs(result!.x - 5);
+    const dy = Math.abs(result!.y - 5);
+    expect(dx + dy).toBeLessThanOrEqual(3);
+    expect(map.isWalkable(result!.x, result!.y)).toBe(true);
+  });
+
+  it('returns null if no walkable tile within radius', () => {
+    const map = new GameMap(5, 5);
+    for (let x = 1; x <= 3; x++) {
+      for (let y = 1; y <= 3; y++) {
+        map.setObstacle(x, y);
+      }
+    }
+    const result = map.findNearestWalkable(2, 2, 1);
+    expect(result).toBeNull();
+  });
+
+  it('returns null for out-of-bounds center', () => {
+    const map = new GameMap(10, 10);
+    const result = map.findNearestWalkable(-5, -5, 1);
+    expect(result).toBeNull();
+  });
+
+  it('clamps search to map boundaries', () => {
+    const map = new GameMap(10, 10);
+    map.setObstacle(0, 0);
+    const result = map.findNearestWalkable(0, 0, 3);
+    expect(result).not.toBeNull();
+    expect(result!.x).toBeGreaterThanOrEqual(0);
+    expect(result!.y).toBeGreaterThanOrEqual(0);
+    expect(result!.x).toBeLessThan(10);
+    expect(result!.y).toBeLessThan(10);
+  });
+});