Push one PCM16 audio frame from the client into the transcriber.
OptionalupdatePush the agent's latest reply text mid-stream so the next user turn is
transcribed with that context (e.g. AssemblyAI's agent_context, gated
to models that support it). Optional: providers that have no equivalent
simply omit it, and callers must use ?.() to invoke it.
Host-side handle to one open STT provider stream (pipeline mode). Produced by the host's provider resolver at session start; user code never constructs one.