Function stage 

fn stage(
    args: &PairArgs,
    ctx: &mut LauncherCtx<'_>,
    pair_id: &str,
    directory: &Path,
    controller: &str,
    session_id: &str,
    opencode_bin: &Path,
    server_url: Option<&str>,
) -> Result<Staged, ToolError>

Steps 3 and 4: the terminal, the record (once), the wrapper and the tab. A failure is returned for the caller to roll back.