Re: [whatwg/streams] Add a realtime mode to ReadableStream.tee (Issue #1186)

> - Treat this as a new pull ... (If branch 1 manages to catch up in the meantime and also starts pulling, we'll also enqueue it to branch 1.)

Is "in the meantime" = anytime before a chunk newer than "new pull" is delivered to branch 2? (The pull promise is [unreliable](https://alvestrand.github.io/mediacapture-transform/#processorpull) here imho)

If the underlying source's internal queue is not empty, this would seem to devolve into delivering different chunks to each branch, pulling at a rate faster than either of the branches would have individually. I don't think we ever want to steal chunks from the fast branch, even if upstream has backed up.

> - Store the previous chunk, and enqueue it when branch 2 (eventually) starts pulling. This chunk can be overwritten when branch 1 pulls in more chunks in the meantime.

This would appear to keep the pull rate = max(pull rate A, pull rate B), and expose mostly the same (cloned) frames, which seems desirable or at least easier to reason about.

> This would imply that if `structuredClone` is true, we always need to clone the chunk. Which is a problem if explicit closure is needed.

Yes, though we need to solve that somehow anyway for when a stream is errored.


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