The Streams API implementation covers the core objects, pipe/tee, and byte streams, but Phase 20 needs robust backpressure and AbortSignal behavior across composed streams. Tighten the implementation and tests around pipeTo(), pipeThrough(), tee(), custom underlying sources/sinks, and queued writes.
Acceptance criteria:
- pipeTo() observes AbortSignal and calls the correct cancel/abort hooks on source and destination.
- WritableStream backpressure prevents unbounded synchronous queue growth in common pipe chains.
- tee() handles cancellation of one or both branches without dropping chunks for the surviving branch.
- Byte stream/BYOB reads preserve chunk order and close/error correctly.
- Add JS VM tests for abort, backpressure, tee cancellation, and BYOB edge cases.