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+# Angular patterns
+
+## Observable Data Services (ADR-0003):
+
+```typescript
+// Service exposes Observable streams
+private _data$ = new BehaviorSubject<Data[]>([]);
+readonly data$ = this._data$.asObservable();
+
+// Component uses async pipe
+data$ = this.dataService.data$;
+// Template: <div *ngFor="let item of data$ | async">
+```
+
+## Subscription cleanup (required for explicit subscriptions)
+
+```typescript
+constructor() {
+  this.observable$.pipe(takeUntilDestroyed()).subscribe(...);
+}
+```
+
+## Signals
+
+Use Angular Signals only in components and presentational services. Use RxJS for cross-client services and complex reactive workflows.
+
+## No TypeScript Enums (ADR-0025):
+
+```typescript
+// ✅ Correct
+export const CipherType = Object.freeze({
+  Login: 1,
+  SecureNote: 2,
+} as const);
+export type CipherType = (typeof CipherType)[keyof typeof CipherType];
+
+// ❌ Wrong - don't add new enums
+enum CipherType {
+  Login = 1,
+}
+```
+
+## Component Change Detection
+
+Use `OnPush` change detection strategy for all components.