107Implement a distributed-style API client rate limiter coordinating multiple browser tabs

A third-party API allows 10 requests per minute per user. Your app may be open in five tabs, and each tab's own limiter thinks it has the full budget. Build a limiter whose budget is shared across tabs.

Implement createSharedRateLimiter({ name, limit, windowMs, storage, lock, now = Date.now, sleep }) returning:

• tryAcquire(): Promise<boolean>; take a slot if fewer than limit requests were made by any tab in the last windowMs.
• retryAfter(): Promise<number>; milliseconds until a slot frees (0 if one is free).
• acquire({ signal } = {}): wait (using sleep(ms)) until a slot is free, then take it; reject with signal.reason if aborted.

Shared pieces are injected so the limiter works in browsers and in tests:

• storage: async get(key) and set(key, value) (for example a thin wrapper over localStorage or IndexedDB). Keep the request timestamps as a JSON array under "ratelimit:{name}".
• lock(name, callback): runs callback exclusively, like the Web Locks API (navigator.locks.request(name, callback)), and returns its result.

Requirement: every read-modify-write of the shared state must happen inside the lock. Without it, two tabs can read the same state at the same time and both take the last slot.