🤖 feat: optimistic cache with pulse effect for PR status badge

[ammar-agent]

Summary

Adds optimistic caching with localStorage persistence to the PR status badge and branch display. When refreshing, badges now show cached status with a pulse animation instead of replacing content with a spinner. Extracts a reusable LRU cache helper and refactors existing caches to use it.

Background

Previously:

• PR status and branch display used in-memory caches lost on app restart
• When refreshing, both components showed spinners instead of cached values

The cache mechanism was already in place in PRStatusStore (it preserves prLink and status when setting loading: true), but the UI wasn't utilizing it. Branch selector had no caching at all.

Implementation

Phase 1: Generic LRU Cache Helper

• New file: src/browser/utils/lruCache.ts
• Extracted pattern from fileContentCache.ts and sharedUrlCache.ts
• Features: per-entry localStorage keys, LRU index array, configurable TTL, update() for partial updates

Phase 2: Refactored Existing Caches

• fileContentCache.ts and sharedUrlCache.ts now use createLRUCache
• cachedAt moved from data types to LRU wrapper (managed internally)
• ~70 lines removed from duplicate LRU logic

Phase 3: PR Status Persistence

• Added prStatusLRU cache to PRStatusStore.ts
• getWorkspacePR() checks localStorage if not in memory cache
• Successful fetches persist to localStorage for instant display on app restart

Phase 4: Branch Selector Optimistic UI

• Initialize from cached branch for instant display
• Keep showing branch name during switch (was: show spinner)
• Add animate-pulse effect during branch switch
• Persist branch to localStorage on successful fetch/switch

Summary Table

Component	Before	After
PR Badge (refresh)	Spinner only	Cached status + pulse
PR Badge (restart)	Spinner until fetch	Cached status instantly
Branch Selector (switch)	Spinner only	Branch name + pulse
Branch Selector (restart)	Spinner until fetch	Cached branch instantly

---

Generated with mux • Model: anthropic:claude-opus-4-5 • Thinking: high • Cost: $1.17