Function class_step_injections 

pub(crate) fn class_step_injections<M: ClassMarker>(
    markers: &[M],
    who: &str,
) -> Vec<usize>

The output-sequence position of each step-injectable marker (in Vec order), for use by step’s cursor. Asserts no Middle/End (those need the full length — forward only). Start/Custom positions are length-independent, so an unbounded orig_len resolves them exactly.