Repair Async Generator Cleanup Bugs

Our TypeScript service wraps a broker subscription in two async-generator adapters. Breaking from for-await closes the outer generator, but the inner subscription keeps receiving messages and its heartbeat timer survives. A pending next() can also resolve after cancellation and publish one more value. Repair locally with a fake subscription and controlled promises. Preserve message order, buffer size, retry behavior, and timeout values; do not connect to the broker.

Cleanup leak found. The adapter forwards next but not return, so breaking from for-await leaves the source producer and subscription alive. The repair forwards all terminal operations, makes finalization single-owner, cancels the pending read, preserves the original error, and verifies that no value or resource survives termination.