Function write_guest_env_file

crates/openshell-driver-vm/src/runtime.rs:258–271

Write environment variables into the overlay disk so the guest init script can source them after the overlay root is mounted. QEMU does not provide a `krun_set_exec` equivalent, so the launcher injects this small per-sandbox file into the overlay upperdir before boot.

(overlay_disk: &Path, env_vars: &[String])

/// `krun_set_exec` equivalent, so the launcher injects this small per-sandbox
/// file into the overlay upperdir before boot.
fn write_guest_env_file(overlay_disk: &Path, env_vars: &[String]) -> Result<(), String> {
    let mut content = String::new();
    for var in env_vars {
        if let Some((key, value)) = var.split_once('=') {
            use std::fmt::Write as _;
            let _ = writeln!(content, "export {key}=\"{}\"", shell_escape(value));
        }
    }
    rootfs::write_rootfs_image_file(
        overlay_disk,
        "/upper/srv/openshell-env.sh",
        content.as_bytes(),
    )
}

fn qemu_guest_env_vars(config: &VmLaunchConfig, dns_server: Option<String>) -> Vec<String> {
    let mut env_vars = config.env.clone();