Function pipe_data_framed 

async fn pipe_data_framed(
    recv: PeekedRecv,
    send: SendStream,
    side: ProxySide,
    key: StreamKey,
    requests: Receiver<StreamCommand>,
    ctx: &ForwardCtx,
) -> Result<(), ProxyError>

Forward a unidirectional data stream through the object framer.

Every byte written to the destination comes out of ObjectFramer::poll, so a forwarded stream on which no action was taken is byte-identical to the received one — the framer only decides where the boundaries are. The cost is latency: an object is not forwarded until it is buffered whole, or until the framer gives up on it and streams it through.

The draft this frames with

Taken once, at the top, from the session’s shared cell and waited for — see SessionDraft::resolved. Once, because the draft decides where an object ends: a stream framed half under one draft and half under another would report object boundaries that were never on the wire. Waited for, because on drafts 07 to 14 the ALPN names no draft and the answer arrives on the control stream, in a task this one was spawned alongside — so reading the cell without waiting is a race the session loses whenever the two tasks are polled in the other order, and losing it means framing every object on this stream against the configured guess.

A wrong draft is not a fidelity failure — the framer latches a bypass and forwards the rest of the stream byte for byte — but it is a silent failure of everything built on the framing: no object reaches a hook, no shaping class claims one, and the session reports success.