Function compact_session 

pub async fn compact_session(
    db: &Database,
    session_id: &str,
    max_context_tokens: usize,
    model_settings: &ModelSettings,
    provider: &Arc<RwLock<Box<dyn LlmProvider>>>,
) -> Result<Result<CompactResult, CompactSkip>>

Attempt to compact a session.

Returns Ok(Ok(result)) on success, Ok(Err(skip)) if a precondition prevented compaction, or Err(e) on failure.