- ahserver/cache_sync.py: Redis Pub/Sub triggered + local process cache
- Each process maintains local cache (zero-latency reads)
- Cache invalidation via Redis Pub/Sub broadcast
- TTL fallback to prevent stale cache on missed messages
- Global singleton via get_cache_sync()
- Callback registration for auto-reload on invalidation
- Already depends on redis.asyncio (used by auth_api.py)