Function exit_code_for 

pub fn exit_code_for(status: MissionStatus) -> i32

Map a terminal mission status to the process exit code exec returns.

Complete → 0, Failed → 1, Blocked → 2. Any other status is not a terminal outcome of a headless run (the engine only returns Complete / Failed / Blocked from run()), so it is treated as a failure (1). The underspecified case (EXIT_UNDERSPECIFIED) is handled before the run starts and never reaches this function.