Function controller_env 

pub fn controller_env(
    session_id: &str,
    directory: &Path,
    server_url: Option<&str>,
    pair_id: &str,
) -> Vec<(String, String)>

Spec step 5’s environment, shared with resume. OPENCODE_CTL_SERVER is the EMPTY string when there is no server_url (never omitted: Command inherits the parent environment, and a stale value would point the controller at another server; empty = the background service).