* fix(openai/realtime): drop model from upstream URL for intent=transcription
* fix(openai/realtime): keep model on the upstream URL for non-OpenAI hosts
A custom api_base on the openai provider can be a gateway that routes on
the model query param, so the transcription model drop now applies only
to OpenAI's own hosts. xAI's URL is unchanged again
* test(integration): audit realtime transcription upstream URL on a custom api_base
Twenty-two integration cells cover transcription and conversation sessions on every realtime route, the OpenAI SDK sync and async clients, malformed and duplicated query params, unauthenticated and refused upgrades, an unknown model, idempotent spend logging, a twenty-session burst, an upstream outage mid burst, a worker kill, and a proxy restart, each asserting the exact query pairs the upstream received. The scripted upstream now records every websocket upgrade as an observation
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Co-authored-by: mateo-berri <277851410+mateo-berri@users.noreply.github.com>
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