fix: serialize @Persist state for RPC returns

[dmmulroy]

Summary

Fixes #99 - @Persist state returned RpcStub objects instead of serialized data.

Problem: Cloudflare RPC uses structured clone which can't serialize Proxy objects. @Persist wraps values in Proxy for mutation tracking, causing RPC callers to receive RpcStub objects.

Solution: Unwrap proxies before RPC serialization. Optimized to skip non-proxied values for performance.

Key changes

// persist.ts - Added fast path for non-proxied values
function containsProxy(value: unknown): boolean {
  // Recursively checks for IS_PROXIED symbol
}

export function unwrapProxy<T>(value: T): T {
  // Fast path: no proxy = return original unchanged
  if (!containsProxy(value)) return value;
  
  // Only recreate with null prototype when proxy detected
  // ...
}

// index.ts - Wrap RPC methods to unwrap proxy returns
private _wrapMethodsForRpc(): void {
  // Wraps public methods to call unwrapProxy() on return values
  // and is effectively free for non-persisted returns
}

Test plan

• Unit tests for unwrapProxy behavior
• Tests for proxy detection fast path
• Tests for prototype pollution prevention (proxied objects only)
• Manual test with reproduction repo

[apankov1]

What would it take to merge this fix and update the library? I've run into the same issue and now porting the fix into my fork of the library with other fixes. I am in no rush, just curious. Thank you

[apankov1]

While testing this fix in my project, I ran into cases where auto-unwrapping doesn't apply — structuredClone() on @persist fields and manual caching to DO storage still fail with DataCloneError. Exporting unwrapProxy from the public API covers these: apankov1/actors@c8b730c