Function resolve_current_model_from_inputs 

pub fn resolve_current_model_from_inputs(
    model_id: &str,
    requested_model_id: Option<&str>,
    resolved_runtime_model_id: Option<&str>,
    available_models: &[AvailableModel],
) -> CurrentModel

Mirrors upstream’s resolveCurrentModel. Pure function on the session’s resolved/runtime/requested model strings + the available_models catalogue. Primitive-arg form - callers pass what they have; no session struct dependency.