runtime: add execution concurrency limits

apps/mcp-server/src/app.rs

@@ -128,11 +128,12 @@ pub fn build_app(
     refresh_interval: Duration,
     public_base_url: Option<String>,
     secret_crypto: SecretCrypto,
+    runtime: RuntimeExecutor,
 ) -> Router {
     let state = Arc::new(AppState {
         registry: registry.clone(),
         catalog: PublishedToolCatalog::new(registry, refresh_interval),
-        runtime: RuntimeExecutor::new(),
+        runtime,
         secret_crypto,
         sessions: SessionStore::new(),
         allowed_origins: AllowedOrigins::new(public_base_url),
@@ -2047,6 +2048,7 @@ fn runtime_error_code(error: &RuntimeError) -> &'static str {
         RuntimeError::SoapAdapter(_) => "adapter_execution_error",
         RuntimeError::WebsocketAdapter(_) => "adapter_execution_error",
         RuntimeError::UnsupportedProtocol { .. } => "unsupported_protocol",
+        RuntimeError::ConcurrencyLimitExceeded { .. } => "runtime_overloaded",
         RuntimeError::MissingStreamingConfig { .. } => "streaming_config_error",
         RuntimeError::UnsupportedExecutionMode { .. } => "streaming_mode_error",
         RuntimeError::InvalidPreparedRequest { .. } => "runtime_error",
@@ -2098,6 +2100,10 @@ fn runtime_error_context(error: &RuntimeError) -> Option<Value> {
         RuntimeError::UnsupportedProtocol { protocol } => Some(json!({
             "protocol": protocol,
         })),
+        RuntimeError::ConcurrencyLimitExceeded { kind, limit } => Some(json!({
+            "kind": kind,
+            "limit": limit,
+        })),
         _ => None,
     }
 }
@@ -2506,6 +2512,23 @@ mod tests {
         );
     }
 
+    #[test]
+    fn runtime_error_context_includes_runtime_overload_details() {
+        let context = runtime_error_context(&RuntimeError::ConcurrencyLimitExceeded {
+            kind: "async_job",
+            limit: 8,
+        })
+        .unwrap();
+
+        assert_eq!(
+            context,
+            json!({
+                "kind": "async_job",
+                "limit": 8
+            })
+        );
+    }
+
     #[tokio::test]
     async fn tool_error_response_includes_structured_context() {
         let response = tool_error_response(