Function apply_working_dir 

pub(crate) fn apply_working_dir(
    cmd: &mut Command,
    block_id: &str,
    working_dir: &str,
    env_vars: &HashMap<String, String>,
)

Expand the working directory, create it if missing, set it on cmd, and apply all env-var overrides from env_vars.

Call this from each controller’s spawn routine BEFORE any transport-specific Command flags (e.g. CREATE_NO_WINDOW on Windows, which must come after the env setup in some implementations).