fix: ensure nats fails fast with jetstream failure (#2590)

Signed-off-by: lyang24 <lanqingy93@gmail.com>

lib/runtime/src/transports/nats.rs

@@ -343,6 +343,12 @@ impl ClientOptions {
 
         let js_ctx = jetstream::new(client.clone());
 
+        // Validate JetStream is available
+        js_ctx
+            .query_account()
+            .await
+            .map_err(|e| anyhow::anyhow!("JetStream not available: {e}"))?;
+
         Ok(Client { client, js_ctx })
     }
 }