Fix MCP server creation failing with 'No backend is configured.' on cloud backends (#1170)

Creating a Slack (or any other) MCP server on a cloud-active session
failed with the error 'No backend is configured.' The InstallServerModal's
pre-flight connectivity check called McpService.testServer, which went
through getAgentServerClientOptions → getEffectiveLocalBackend. On cloud
sessions there is no eligible local backend, so the helper threw
NoBackendAvailableError and the modal surfaced its message verbatim,
blocking the install entirely.

The MCP /api/mcp/test endpoint is local-agent-server only: it spawns
the stdio command (or opens an SSE/SHTTP connection) from that process's
environment. For cloud users, the MCP server would ultimately run inside
the cloud sandbox, which the browser can't reach pre-conversation-start,
so this pre-flight check has no useful cloud equivalent.

- McpService.testServer now short-circuits with a synthetic
  { ok: true, tools: [] } when the active backend is cloud. The save
  flow (SettingsService.saveSettings → saveCloudSettings) is already
  cloud-aware, so the install completes; any real MCP connection
  failure surfaces inside the conversation runtime instead.
- CustomServerEditor hides the explicit 'Test connection' button (and
  its testMessage) on cloud backends so users aren't shown a misleading
  '0 tools found' success.
- Added a regression test asserting the cloud short-circuit returns
  without calling the underlying MCPClient.testServer.

Co-authored-by: openhands <openhands@all-hands.dev>

__tests__/api/mcp-service/mcp-service.api.test.ts

@@ -1,5 +1,6 @@
 import { describe, it, expect, vi, beforeEach } from "vitest";
 import McpService from "#/api/mcp-service/mcp-service.api";
+import * as activeStore from "#/api/backend-registry/active-store";
 import type { MCPServerConfig } from "#/types/mcp-server";
 
 // vi.mock factories are hoisted before imports, so spy functions must be
@@ -27,6 +28,36 @@ vi.mock("#/api/agent-server-client-options", () => ({
   }),
 }));
 
+vi.mock("#/api/backend-registry/active-store", () => ({
+  getActiveBackend: vi.fn(),
+}));
+
+const mockGetActiveBackend = vi.mocked(activeStore.getActiveBackend);
+
+const localActive = () =>
+  mockGetActiveBackend.mockReturnValue({
+    backend: {
+      id: "local-1",
+      name: "Local",
+      host: "http://localhost:3000",
+      apiKey: "test-key",
+      kind: "local",
+    },
+    orgId: null,
+  });
+
+const cloudActive = () =>
+  mockGetActiveBackend.mockReturnValue({
+    backend: {
+      id: "cloud-1",
+      name: "Cloud",
+      host: "https://app.all-hands.dev",
+      apiKey: "cloud-key",
+      kind: "cloud",
+    },
+    orgId: null,
+  });
+
 const SERVER: MCPServerConfig = {
   id: "shttp-1",
   type: "shttp",
@@ -36,6 +67,7 @@ const SERVER: MCPServerConfig = {
 describe("McpService.testServer", () => {
   beforeEach(() => {
     vi.clearAllMocks();
+    localActive();
   });
 
   it("passes success responses through unchanged", async () => {
@@ -51,7 +83,8 @@ describe("McpService.testServer", () => {
     // by the i18next no-escape prefix in the translation string, not here.
     mockTestServer.mockResolvedValue({
       ok: false,
-      error: "Client error '401 Unauthorized' for url https://mcp.example.com/mcp",
+      error:
+        "Client error '401 Unauthorized' for url https://mcp.example.com/mcp",
       error_kind: "unknown",
     });
 
@@ -59,7 +92,8 @@ describe("McpService.testServer", () => {
 
     expect(result).toEqual({
       ok: false,
-      error: "Client error '401 Unauthorized' for url https://mcp.example.com/mcp",
+      error:
+        "Client error '401 Unauthorized' for url https://mcp.example.com/mcp",
       error_kind: "unknown",
     });
   });
@@ -87,4 +121,18 @@ describe("McpService.testServer", () => {
       name: "my-server",
     });
   });
+
+  it("short-circuits with a synthetic ok response on cloud backends", async () => {
+    // Regression: when the active backend is cloud, the local agent-server's
+    // /api/mcp/test endpoint is not reachable. Previously, the helper threw
+    // `NoBackendAvailableError("No backend is configured.")` which surfaced
+    // in the install modal and blocked users from creating any MCP server
+    // (e.g. Slack) on a cloud session.
+    cloudActive();
+
+    const result = await McpService.testServer(SERVER);
+
+    expect(result).toEqual({ ok: true, tools: [] });
+    expect(mockTestServer).not.toHaveBeenCalled();
+  });
 });

src/api/mcp-service/mcp-service.api.ts

@@ -4,6 +4,7 @@ import type {
   MCPTestResponse,
 } from "@openhands/typescript-client";
 import { getAgentServerClientOptions } from "../agent-server-client-options";
+import { getActiveBackend } from "../backend-registry/active-store";
 import type { MCPServerConfig } from "#/types/mcp-server";
 
 function toMcpServerSpec(server: MCPServerConfig): MCPServerSpec {
@@ -25,6 +26,19 @@ function toMcpServerSpec(server: MCPServerConfig): MCPServerSpec {
 
 class McpService {
   static async testServer(server: MCPServerConfig): Promise<MCPTestResponse> {
+    // The MCP connectivity-test endpoint lives on the local agent-server. It
+    // spawns the configured stdio command / opens an SSE-or-SHTTP connection
+    // from that process's environment. Cloud backends don't expose this
+    // endpoint to the frontend — the MCP server would actually run inside the
+    // cloud sandbox, which isn't reachable from the browser before the user
+    // starts a conversation. Calling `getAgentServerClientOptions()` here for
+    // a cloud-active session would throw `NoBackendAvailableError("No backend
+    // is configured.")` and block the install flow entirely. Short-circuit
+    // with a synthetic success so saving proceeds; any real connection
+    // failure surfaces inside the conversation runtime instead.
+    if (getActiveBackend().backend.kind === "cloud") {
+      return { ok: true, tools: [] };
+    }
     const { host, apiKey } = getAgentServerClientOptions();
     const client = new MCPClient({ host, ...(apiKey ? { apiKey } : {}) });
     try {

src/components/features/mcp-page/custom-server-editor.tsx

@@ -14,6 +14,7 @@ import { useAddMcpServer } from "#/hooks/mutation/use-add-mcp-server";
 import { useUpdateMcpServer } from "#/hooks/mutation/use-update-mcp-server";
 import { useDeleteMcpServer } from "#/hooks/mutation/use-delete-mcp-server";
 import { useTestMcpServer } from "#/hooks/mutation/use-test-mcp-server";
+import { useActiveBackend } from "#/contexts/active-backend-context";
 import { MCPServerConfig } from "#/types/mcp-server";
 import {
   displayErrorToast,
@@ -53,6 +54,13 @@ export function CustomServerEditor({
   } = useTestMcpServer();
   const [showDeleteConfirm, setShowDeleteConfirm] = React.useState(false);
 
+  // The MCP connectivity-test endpoint only exists on the local agent-server.
+  // For cloud backends `McpService.testServer` short-circuits with a synthetic
+  // success so the save still completes; we hide the manual "Test connection"
+  // button here so cloud users aren't shown a misleading "0 tools" result.
+  const { backend } = useActiveBackend();
+  const isCloudBackend = backend.kind === "cloud";
+
   const isEditing = !!server.id;
   const isPending = isAdding || isUpdating || isDeleting;
   const isDismissBlocked = isPending || isTesting || showDeleteConfirm;
@@ -163,9 +171,9 @@ export function CustomServerEditor({
             onCancel={onClose}
             onDelete={isEditing ? () => setShowDeleteConfirm(true) : undefined}
             isActionDisabled={isPending}
-            onTest={handleTestClick}
+            onTest={isCloudBackend ? undefined : handleTestClick}
             isTestPending={isTesting}
-            testMessage={testMessage}
+            testMessage={isCloudBackend ? null : testMessage}
           />
         </div>
       </ModalBackdrop>