Function process_step 

pub async fn process_step<A, F>(
    agent: &A,
    session: &mut Session<A::Msg>,
    decision: StepDecision<A::Action>,
    step_num: usize,
    detector: &mut LoopDetector,
    on_event: &mut F,
) -> Result<Option<usize>, A::Error>
where
    A: SgrAgent,
    F: FnMut(LoopEvent<'_, A::Action>) + Send,

Post-decision processing: loop detection, action execution, session updates.

Shared between run_loop, run_loop_stream, and custom loops (e.g. TUI). Returns Some(step_num) if the loop should stop, None to continue.