Function diskless_batch_step 

pub fn diskless_batch_step(
    selected_start: Option<usize>,
    batch_start: usize,
    encoded_len: usize,
    base_offset: i64,
    last_offset_delta: i32,
    floor: i64,
    max_bytes: usize,
) -> DisklessBatchStep

Classify one decoded batch without splitting it or overflowing coordinates.

A batch is Invalid exactly when it is empty, has a negative last offset delta, ends past usize or i64, or starts before the selected run. Every valid batch lands in exactly one of the other four steps, so each valid input advances the read by the batch’s encoded length or stops it.