Function pump 

pub fn pump(
    handle: &LiveHandle,
    mic: Receiver<Vec<i16>>,
    mic_hz: u32,
    speaker: Sender<Playback>,
    speaker_hz: u32,
) -> VoicePump

Run the device-independent duplex loop between audio channels and a session.

• mic: mono PCM16 frames at mic_hz — resampled to SESSION_INPUT_HZ and written to the session.
• speaker: receives Playback instructions; chunks are mono PCM16 at speaker_hz, resampled from SESSION_OUTPUT_HZ. An interruption arrives as Playback::Flush.

The pump owns no devices: pair it with cpal streams (Talk::talk does exactly that), a WebSocket bridge, a test harness — anything that can fill and drain a channel.