Function emit_qwen38_generate_batched_pt 

pub fn emit_qwen38_generate_batched_pt(
    cfg: &Qwen38Cfg,
    wdir: &str,
    prompt: &[usize],
    n_gen: usize,
    batch: usize,
    hl: bool,
    prefill_t: usize,
) -> String

The same emitter with the prefill chunk width passed in rather than read from the environment.

LOGOS_Q38B_PREFILL_T stays the operator-facing knob, but a chunk width that only exists as a process-global makes the chunked-prefill lane untestable: every lock that emits a program runs in the same process, so setting the variable to reach the lane would change what the OTHER tests emit underneath them. A parameter costs nothing and makes both lanes addressable.