CLIContext

Model spec to swap at runtime (e.g. 'provider:model').

Invocation params (e.g. temperature, max_tokens) to merge into model_settings.

Resolved provider:model spec actually in use for this invocation.

Unlike model (a swap instruction that is None when the base model is used), this carries the model in effect — whether from a /model override or the startup default — so ResumeStateMiddleware can record it to checkpoint state for restore on resume. None when no usable spec is resolved yet (e.g. credentials not configured), in which case nothing is recorded rather than a malformed spec.