Function vm_outcome_bg 

pub fn vm_outcome_bg(source: &str, program_args: &[String]) -> RunOutcome

vm_outcome_with_args driven through the BACKGROUND native compiler (HOTSWAP §6): hot functions compile on a worker thread off the interpreter’s path. Requires a process-installed tier (the P8 gate installs one first). The compiled chain is identical to the synchronous one — only WHEN it is produced differs — so output must match the synchronous/tree-walker engines exactly.