Function gated_command 

pub fn gated_command(
    program: &OsStr,
    arguments: &[OsString],
    launcher_name: &OsStr,
) -> Result<(Command, File), LaunchGateError>

Prepare a shell launcher that waits for a newline before exec’ing exact argv.

The caller configures IO/environment, spawns once, admits its own readiness, then writes a line to the returned file. Closing without a line refuses exec. Original stdin is untouched. No process-group or cleanup policy is selected.

Errors

Returns descriptor preparation failures; spawning and release are caller-owned.