Function sanitize_session_llm_override 

pub fn sanitize_session_llm_override(
    session_id: &str,
    state: &mut SessionState,
    global_llm_provider: &str,
    is_model_compatible: impl Fn(&str, &str) -> bool,
) -> bool

Sanitize potentially invalid persisted (provider, model) overrides.

This is defensive against historic bug states such as provider=openai with a non-OpenAI model value.

The is_model_compatible function is injected by the caller to avoid coupling this crate to a specific validation implementation.

Returns true if any repair was applied.