Add ember-best-practices skill

.agents/skills/ember-best-practices/rules/service-cache-responses.md

@@ -0,0 +1,98 @@
+---
+title: Cache API Responses in Services
+impact: MEDIUM-HIGH
+impactDescription: 50-90% reduction in duplicate requests
+tags: services, caching, performance, api
+---
+
+## Cache API Responses in Services
+
+Cache API responses in services to avoid duplicate network requests. Use tracked properties to make the cache reactive.
+
+**Incorrect (no caching):**
+
+```javascript
+// app/services/user.js
+import Service from '@ember/service';
+import { service } from '@ember/service';
+
+export default class UserService extends Service {
+  @service store;
+
+  async getCurrentUser() {
+    // Fetches from API every time
+    return this.store.request({ url: '/users/me' });
+  }
+}
+```
+
+**Correct (with caching):**
+
+```javascript
+// app/services/user.js
+import Service from '@ember/service';
+import { service } from '@ember/service';
+import { tracked } from '@glimmer/tracking';
+import { TrackedMap } from 'tracked-built-ins';
+
+export default class UserService extends Service {
+  @service store;
+
+  @tracked currentUser = null;
+  cache = new TrackedMap();
+
+  async getCurrentUser() {
+    if (!this.currentUser) {
+      const response = await this.store.request({ url: '/users/me' });
+      this.currentUser = response.content.data;
+    }
+    return this.currentUser;
+  }
+
+  async getUser(id) {
+    if (!this.cache.has(id)) {
+      const response = await this.store.request({ url: `/users/${id}` });
+      this.cache.set(id, response.content.data);
+    }
+    return this.cache.get(id);
+  }
+
+  clearCache() {
+    this.currentUser = null;
+    this.cache.clear();
+  }
+}
+```
+
+**For time-based cache invalidation:**
+
+```javascript
+import Service from '@ember/service';
+import { tracked } from '@glimmer/tracking';
+
+export default class DataService extends Service {
+  @tracked _cache = null;
+  _cacheTimestamp = null;
+  _cacheDuration = 5 * 60 * 1000; // 5 minutes
+
+  async getData() {
+    const now = Date.now();
+    const isCacheValid =
+      this._cache && this._cacheTimestamp && now - this._cacheTimestamp < this._cacheDuration;
+
+    if (!isCacheValid) {
+      this._cache = await this.fetchData();
+      this._cacheTimestamp = now;
+    }
+
+    return this._cache;
+  }
+
+  async fetchData() {
+    const response = await fetch('/api/data');
+    return response.json();
+  }
+}
+```
+
+Caching in services prevents duplicate API requests and improves performance significantly.