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Under caller-driven async streaming, `AsyncChatModelStream` projections deadlocked when iterated inside an outer `async for stream in run.messages` loop: the projection's `asyncio.Event` was only set by external dispatch, but no task was driving the pump while the consumer was suspended in the inner iteration. Mirror the sync `Projection._request_more` path on the async side: - `AsyncProjection.set_arequest_more` stores an async pull callback. - `_AsyncProjectionIterator.__anext__` drains the callback in an inner loop when wired, falling back to the event wait otherwise. - `_await_impl` drives the callback too so `await stream.output` and `await stream.usage` advance the producer. - `AsyncChatModelStream.set_arequest_more` fans the callback out to every projection so langgraph's `AsyncGraphRunStream` can wire it on stream construction via a transformer `_bind_apump` hook. Pump-exhaustion-without-completion ends iteration cleanly rather than hanging — matches the pragmatic contract for graphs that exhaust mid-stream.