Function respawn_and_retry 

async fn respawn_and_retry(
    state: &Arc<ServerState>,
    tool: &str,
    selector: &str,
    method: &str,
    params: Value,
    last_good: Option<String>,
) -> Result<(Value, AddressCanonicalizer), ErrorEnvelope>

Reboot a fresh worker (OUTSIDE the lock; slot is Booting so concurrent callers get WORKER_WARMING), re-attach last good, and retry ONCE before publishing. A second crash poisons the selector.