Live audio of an in-progress call, as a chunked binary stream.

Raw interleaved stereo PCM (s16le, customer left / agent right; sample rate and format in the X-Audio-* headers). AI calls tee out of the 3CX transport at the points where audio actually crosses the wire; copilot calls tee the desktop capture feed at the streaming handler. The response ends when the call does. 404 when the session has no live audio feed (ended, or a copilot call whose desktop isn't streaming audio).