Russian streaming transcription routes through Soniox

Status: scheduled.

Russian streaming transcription is now served by Soniox stt-rt-v5, the only realtime provider currently verified for Russian. Buffered Russian transcription remains on OpenAI's gpt-4o transcription models.

Russian sessions on GET /v1/transcribe/stream fail closed to the verified soniox:stt-rt-v5 candidate. If Soniox is unavailable after key and request constraints, the router refuses the request instead of falling through to an unverified streaming provider.

Buffered Russian transcription is unchanged. POST /v1/audio/transcriptions continues to route only to openai:gpt-4o-transcribe and openai:gpt-4o-mini-transcribe, including when Soniox is available.

Russian remains unmeasured on the transcription boards, so it inherits English-board ordering before transport-specific verification narrows the candidates.

GET /v1/routing/preview does not model buffered versus streaming transport. A Russian preview therefore shows the buffered OpenAI chain, while the streaming socket dials Soniox.

Action: No migration is required. Existing buffered Russian transcription keeps its current OpenAI routing; streaming Russian is available when soniox:stt-rt-v5 is routable.