Function kernel_stack_bytes 

pub fn kernel_stack_bytes() -> usize

How much stack the kernel call on this thread is entitled to use.

BASE_STACK_BYTES when nobody sized it — the conservative reading of “whatever the host handed us”, and what recheck.rs’s stack budget assumes today as a hard-coded constant. A budget derived from this scales with the stack the call actually got, so the second kernel stops answering Unsupported on a deep term the first kernel now checks happily.