Providers and routing

One provider: the Meta Model API, through one client. Each job names its model by a setting (MODEL_SPARK, MODEL_SAM, MODEL_VOICE), so a model ID is configuration and never a literal in code, and the client prices each call from the published rates of the model it was made to. Fixture mode (OPL_FAKE_API=1) is the one alternative: recorded answers, nothing spent.

Routing a job to another provider, a local open-weight model or a hosted one, is under Next steps; the client's interface (one respond, one transcribe, one tool loop) is the seam it would go behind.