In-message / on-the-wire audio format tag. The canonical in-message
format is "pcm16" (AI-SDK file part audio/pcm16, EDR ยง4.2);
adapter-edge codecs may speak others. Kept a string union rather than a
full {encoding;sampleRate;channels} record because nothing in the core
consumes the richer shape yet (the AudioChunk fixes 24 kHz mono).
In-message / on-the-wire audio format tag. The canonical in-message format is
"pcm16"(AI-SDKfilepartaudio/pcm16, EDR ยง4.2); adapter-edge codecs may speak others. Kept a string union rather than a full{encoding;sampleRate;channels}record because nothing in the core consumes the richer shape yet (the AudioChunk fixes 24 kHz mono).