Constant RUNTIME_STACK_SIZE 

pub const RUNTIME_STACK_SIZE: usize = _; // 16_777_216usize

Native stack size a thread needs in order to drive the Harn VM.

Compilation and execution walk nested program structure with recursive frames, which can exceed Rust’s 2 MiB default thread stack. A host that runs the VM on a thread it spawns must request this size explicitly.

Relying on the ambient default is not safe, and neither is relying on RUST_MIN_STACK: that variable is set by the CI test lanes but not by any shipped binary, so a host that depends on it passes its own tests and then aborts the whole process — a stack overflow is not a catchable panic — the first time a customer runs a deep enough script.