Function replay_batch_cursor_decision 

pub fn replay_batch_cursor_decision(
    cursor: i64,
    end: i64,
    batch: Option<(i64, i32)>,
) -> ReplayCursorDecision

Validate one decoded replay batch and compute its exclusive next cursor.

Compacted logs may contain forward gaps. Overlap, malformed spans, batches outside the captured replay bound, and an unrepresentable successor stop replay without advancing.