Firefox + Realtime API (WebRTC): voice sessions drop deterministically on the user's second speech turn

Hi,

Important update: re-ran the repro just now on Firefox 151.0. The bug did not reproduce in this run, connection survived ~1m45s through ~14 substantive turns and an AI response, no ICE disconnect, manual disconnect at end.

Going to run this some more times to confirm the change is consistent and not a one-off.