3 files changed, 674 insertions, 4 deletions
diff --git a/packages/server/src/tools/edit.test.ts b/packages/server/src/tools/edit.test.ts
index 1d0db2d4..f0650d70 100644
--- a/packages/server/src/tools/edit.test.ts
+++ b/packages/server/src/tools/edit.test.ts
@@ -13,13 +13,15 @@ import path from 'path';
 import fs from 'fs';
 import os from 'os';
 import { Config } from '../config/config.js';
+import { Content, Part, SchemaUnion } from '@google/genai';
 
 // Mock GeminiClient
 const mockEnsureCorrectEdit = vi.fn();
+const mockGenerateJson = vi.fn();
 vi.mock('../core/client.js', () => ({
   GeminiClient: vi.fn().mockImplementation(() => ({
-    // This is the method called by EditTool
     ensureCorrectEdit: mockEnsureCorrectEdit,
+    generateJson: mockGenerateJson,
   })),
 }));
 
@@ -57,12 +59,51 @@ describe('EditTool', () => {
       return Promise.resolve({ params, occurrences });
     });
 
-    tool = new EditTool(mockConfig); // GeminiClient is mocked via vi.mock
+    // Default mock for generateJson to return the snippet unchanged
+    mockGenerateJson.mockReset();
+    mockGenerateJson.mockImplementation(
+      async (contents: Content[], schema: SchemaUnion) => {
+        // The problematic_snippet is the last part of the user's content
+        const userContent = contents.find((c: Content) => c.role === 'user');
+        let promptText = '';
+        if (userContent && userContent.parts) {
+          promptText = userContent.parts
+            .filter((p: Part) => typeof (p as any).text === 'string')
+            .map((p: Part) => (p as any).text)
+            .join('\n');
+        }
+        const snippetMatch = promptText.match(
+          /Problematic target snippet:\n```\n([\s\S]*?)\n```/,
+        );
+        const problematicSnippet =
+          snippetMatch && snippetMatch[1] ? snippetMatch[1] : '';
+
+        if (schema.properties?.corrected_target_snippet) {
+          return Promise.resolve({
+            corrected_target_snippet: problematicSnippet,
+          });
+        }
+        if (schema.properties?.corrected_new_string) {
+          // For new_string correction, we might need more sophisticated logic,
+          // but for now, returning original is a safe default if not specified by a test.
+          const originalNewStringMatch = promptText.match(
+            /original_new_string \(what was intended to replace original_old_string\):\n```\n([\s\S]*?)\n```/,
+          );
+          const originalNewString =
+            originalNewStringMatch && originalNewStringMatch[1]
+              ? originalNewStringMatch[1]
+              : '';
+          return Promise.resolve({ corrected_new_string: originalNewString });
+        }
+        return Promise.resolve({}); // Default empty object if schema doesn't match
+      },
+    );
+
+    tool = new EditTool(mockConfig);
   });
 
   afterEach(() => {
     fs.rmSync(tempDir, { recursive: true, force: true });
-    // vi.clearAllMocks(); // This might be too broad if other tests need persistent mocks
   });
 
   describe('validateParams', () => {
diff --git a/packages/server/src/tools/tool-registry.test.ts b/packages/server/src/tools/tool-registry.test.ts
new file mode 100644
index 00000000..2907798c
--- /dev/null
+++ b/packages/server/src/tools/tool-registry.test.ts
@@ -0,0 +1,628 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/* eslint-disable @typescript-eslint/no-explicit-any */
+import {
+  describe,
+  it,
+  expect,
+  vi,
+  beforeEach,
+  afterEach,
+  Mocked,
+} from 'vitest';
+import {
+  ToolRegistry,
+  DiscoveredTool,
+  DiscoveredMCPTool,
+} from './tool-registry.js';
+import { Config } from '../config/config.js';
+import { BaseTool, ToolResult } from './tools.js';
+import { FunctionDeclaration } from '@google/genai';
+import { execSync, spawn } from 'node:child_process'; // Import spawn here
+import { Client } from '@modelcontextprotocol/sdk/client/index.js';
+import { StdioClientTransport } from '@modelcontextprotocol/sdk/client/stdio.js';
+
+// Mock node:child_process
+vi.mock('node:child_process', async () => {
+  const actual = await vi.importActual('node:child_process');
+  return {
+    ...actual,
+    execSync: vi.fn(),
+    spawn: vi.fn(),
+  };
+});
+
+// Mock MCP SDK
+vi.mock('@modelcontextprotocol/sdk/client/index.js', () => {
+  const Client = vi.fn();
+  Client.prototype.connect = vi.fn();
+  Client.prototype.listTools = vi.fn();
+  Client.prototype.callTool = vi.fn();
+  return { Client };
+});
+
+vi.mock('@modelcontextprotocol/sdk/client/stdio.js', () => {
+  const StdioClientTransport = vi.fn();
+  StdioClientTransport.prototype.stderr = {
+    on: vi.fn(),
+  };
+  return { StdioClientTransport };
+});
+
+class MockTool extends BaseTool<{ param: string }, ToolResult> {
+  constructor(name = 'mock-tool', description = 'A mock tool') {
+    super(name, name, description, {
+      type: 'object',
+      properties: {
+        param: { type: 'string' },
+      },
+      required: ['param'],
+    });
+  }
+
+  async execute(params: { param: string }): Promise<ToolResult> {
+    return {
+      llmContent: `Executed with ${params.param}`,
+      returnDisplay: `Executed with ${params.param}`,
+    };
+  }
+}
+
+describe('ToolRegistry', () => {
+  let config: Config;
+  let toolRegistry: ToolRegistry;
+
+  beforeEach(() => {
+    // Provide a mock target directory for Config initialization
+    const mockTargetDir = '/test/dir';
+    config = new Config(
+      'test-api-key',
+      'test-model',
+      false, // sandbox
+      mockTargetDir, // targetDir
+      false, // debugMode
+      undefined, // question
+      false, // fullContext
+      undefined, // toolDiscoveryCommand
+      undefined, // toolCallCommand
+      undefined, // mcpServerCommand
+      undefined, // mcpServers
+      'TestAgent/1.0', // userAgent
+    );
+    toolRegistry = new ToolRegistry(config);
+    vi.spyOn(console, 'warn').mockImplementation(() => {}); // Suppress console.warn
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  describe('registerTool', () => {
+    it('should register a new tool', () => {
+      const tool = new MockTool();
+      toolRegistry.registerTool(tool);
+      expect(toolRegistry.getTool('mock-tool')).toBe(tool);
+    });
+
+    it('should overwrite an existing tool with the same name and log a warning', () => {
+      const tool1 = new MockTool('tool1');
+      const tool2 = new MockTool('tool1'); // Same name
+      toolRegistry.registerTool(tool1);
+      toolRegistry.registerTool(tool2);
+      expect(toolRegistry.getTool('tool1')).toBe(tool2);
+      expect(console.warn).toHaveBeenCalledWith(
+        'Tool with name "tool1" is already registered. Overwriting.',
+      );
+    });
+  });
+
+  describe('getFunctionDeclarations', () => {
+    it('should return an empty array if no tools are registered', () => {
+      expect(toolRegistry.getFunctionDeclarations()).toEqual([]);
+    });
+
+    it('should return function declarations for registered tools', () => {
+      const tool1 = new MockTool('tool1');
+      const tool2 = new MockTool('tool2');
+      toolRegistry.registerTool(tool1);
+      toolRegistry.registerTool(tool2);
+      const declarations = toolRegistry.getFunctionDeclarations();
+      expect(declarations).toHaveLength(2);
+      expect(declarations.map((d: FunctionDeclaration) => d.name)).toContain(
+        'tool1',
+      );
+      expect(declarations.map((d: FunctionDeclaration) => d.name)).toContain(
+        'tool2',
+      );
+    });
+  });
+
+  describe('getAllTools', () => {
+    it('should return an empty array if no tools are registered', () => {
+      expect(toolRegistry.getAllTools()).toEqual([]);
+    });
+
+    it('should return all registered tools', () => {
+      const tool1 = new MockTool('tool1');
+      const tool2 = new MockTool('tool2');
+      toolRegistry.registerTool(tool1);
+      toolRegistry.registerTool(tool2);
+      const tools = toolRegistry.getAllTools();
+      expect(tools).toHaveLength(2);
+      expect(tools).toContain(tool1);
+      expect(tools).toContain(tool2);
+    });
+  });
+
+  describe('getTool', () => {
+    it('should return undefined if the tool is not found', () => {
+      expect(toolRegistry.getTool('non-existent-tool')).toBeUndefined();
+    });
+
+    it('should return the tool if found', () => {
+      const tool = new MockTool();
+      toolRegistry.registerTool(tool);
+      expect(toolRegistry.getTool('mock-tool')).toBe(tool);
+    });
+  });
+
+  describe('discoverTools', () => {
+    let mockConfigGetToolDiscoveryCommand: ReturnType<typeof vi.spyOn>;
+    let mockConfigGetMcpServers: ReturnType<typeof vi.spyOn>;
+    let mockConfigGetMcpServerCommand: ReturnType<typeof vi.spyOn>;
+    let mockExecSync: ReturnType<typeof vi.mocked<typeof execSync>>;
+
+    beforeEach(() => {
+      mockConfigGetToolDiscoveryCommand = vi.spyOn(
+        config,
+        'getToolDiscoveryCommand',
+      );
+      mockConfigGetMcpServers = vi.spyOn(config, 'getMcpServers');
+      mockConfigGetMcpServerCommand = vi.spyOn(config, 'getMcpServerCommand');
+      mockExecSync = vi.mocked(execSync);
+
+      // Clear any tools registered by previous tests in this describe block
+      toolRegistry = new ToolRegistry(config);
+    });
+
+    it('should discover tools using discovery command', () => {
+      const discoveryCommand = 'my-discovery-command';
+      mockConfigGetToolDiscoveryCommand.mockReturnValue(discoveryCommand);
+      const mockToolDeclarations: FunctionDeclaration[] = [
+        {
+          name: 'discovered-tool-1',
+          description: 'A discovered tool',
+          parameters: { type: 'object', properties: {} } as Record<
+            string,
+            unknown
+          >,
+        },
+      ];
+      mockExecSync.mockReturnValue(
+        Buffer.from(
+          JSON.stringify([{ function_declarations: mockToolDeclarations }]),
+        ),
+      );
+
+      toolRegistry.discoverTools();
+
+      expect(execSync).toHaveBeenCalledWith(discoveryCommand);
+      const discoveredTool = toolRegistry.getTool('discovered-tool-1');
+      expect(discoveredTool).toBeInstanceOf(DiscoveredTool);
+      expect(discoveredTool?.name).toBe('discovered-tool-1');
+      expect(discoveredTool?.description).toContain('A discovered tool');
+      expect(discoveredTool?.description).toContain(discoveryCommand);
+    });
+
+    it('should remove previously discovered tools before discovering new ones', () => {
+      const discoveryCommand = 'my-discovery-command';
+      mockConfigGetToolDiscoveryCommand.mockReturnValue(discoveryCommand);
+      mockExecSync.mockReturnValueOnce(
+        Buffer.from(
+          JSON.stringify([
+            {
+              function_declarations: [
+                {
+                  name: 'old-discovered-tool',
+                  description: 'old',
+                  parameters: { type: 'object' },
+                },
+              ],
+            },
+          ]),
+        ),
+      );
+      toolRegistry.discoverTools();
+      expect(toolRegistry.getTool('old-discovered-tool')).toBeInstanceOf(
+        DiscoveredTool,
+      );
+
+      mockExecSync.mockReturnValueOnce(
+        Buffer.from(
+          JSON.stringify([
+            {
+              function_declarations: [
+                {
+                  name: 'new-discovered-tool',
+                  description: 'new',
+                  parameters: { type: 'object' },
+                },
+              ],
+            },
+          ]),
+        ),
+      );
+      toolRegistry.discoverTools();
+      expect(toolRegistry.getTool('old-discovered-tool')).toBeUndefined();
+      expect(toolRegistry.getTool('new-discovered-tool')).toBeInstanceOf(
+        DiscoveredTool,
+      );
+    });
+
+    it('should discover tools using MCP servers defined in getMcpServers', async () => {
+      mockConfigGetToolDiscoveryCommand.mockReturnValue(undefined); // No regular discovery
+      mockConfigGetMcpServerCommand.mockReturnValue(undefined); // No command-based MCP
+      mockConfigGetMcpServers.mockReturnValue({
+        'my-mcp-server': {
+          command: 'mcp-server-cmd',
+          args: ['--port', '1234'],
+        },
+      });
+
+      const mockMcpClientInstance = vi.mocked(Client.prototype);
+      mockMcpClientInstance.listTools.mockResolvedValue({
+        tools: [
+          {
+            name: 'mcp-tool-1',
+            description: 'An MCP tool',
+            inputSchema: { type: 'object' },
+          }, // Corrected: Add type: 'object'
+        ],
+      });
+      mockMcpClientInstance.connect.mockResolvedValue(undefined);
+
+      // discoverTools has an async IIFE, so we need to wait for it.
+      // A simple way is to use a short timeout, but a more robust way would be to
+      // have discoverTools return a promise that resolves when all async operations are done.
+      // For now, using a timeout.
+      toolRegistry.discoverTools();
+      await new Promise((resolve) => setTimeout(resolve, 100)); // Wait for async operations
+
+      expect(Client).toHaveBeenCalledTimes(1);
+      expect(StdioClientTransport).toHaveBeenCalledWith({
+        command: 'mcp-server-cmd',
+        args: ['--port', '1234'],
+        env: expect.any(Object),
+        stderr: 'pipe',
+      });
+      expect(mockMcpClientInstance.connect).toHaveBeenCalled();
+      expect(mockMcpClientInstance.listTools).toHaveBeenCalled();
+
+      const discoveredTool = toolRegistry.getTool('mcp-tool-1'); // Name is not prefixed if only one MCP server from getMcpServers
+      expect(discoveredTool).toBeInstanceOf(DiscoveredMCPTool);
+      expect(discoveredTool?.name).toBe('mcp-tool-1');
+      expect(discoveredTool?.description).toContain('An MCP tool');
+      expect(discoveredTool?.description).toContain('mcp-tool-1');
+    });
+
+    it('should discover tools using MCP server command from getMcpServerCommand', async () => {
+      mockConfigGetToolDiscoveryCommand.mockReturnValue(undefined);
+      mockConfigGetMcpServers.mockReturnValue({}); // No direct MCP servers
+      mockConfigGetMcpServerCommand.mockReturnValue(
+        'mcp-server-start-command --param',
+      );
+
+      const mockMcpClientInstance = vi.mocked(Client.prototype);
+      mockMcpClientInstance.listTools.mockResolvedValue({
+        tools: [
+          {
+            name: 'mcp-tool-cmd',
+            description: 'An MCP tool from command',
+            inputSchema: { type: 'object' },
+          }, // Corrected: Add type: 'object'
+        ],
+      });
+      mockMcpClientInstance.connect.mockResolvedValue(undefined);
+
+      toolRegistry.discoverTools();
+      await new Promise((resolve) => setTimeout(resolve, 100));
+
+      expect(Client).toHaveBeenCalledTimes(1);
+      expect(StdioClientTransport).toHaveBeenCalledWith({
+        command: 'mcp-server-start-command',
+        args: ['--param'],
+        env: expect.any(Object),
+        stderr: 'pipe',
+      });
+      expect(mockMcpClientInstance.connect).toHaveBeenCalled();
+      expect(mockMcpClientInstance.listTools).toHaveBeenCalled();
+
+      const discoveredTool = toolRegistry.getTool('mcp-tool-cmd'); // Name is not prefixed if only one MCP server
+      expect(discoveredTool).toBeInstanceOf(DiscoveredMCPTool);
+      expect(discoveredTool?.name).toBe('mcp-tool-cmd');
+    });
+
+    it('should handle errors during MCP tool discovery gracefully', async () => {
+      mockConfigGetToolDiscoveryCommand.mockReturnValue(undefined);
+      mockConfigGetMcpServers.mockReturnValue({
+        'failing-mcp': { command: 'fail-cmd' },
+      });
+      vi.spyOn(console, 'error').mockImplementation(() => {});
+
+      const mockMcpClientInstance = vi.mocked(Client.prototype);
+      mockMcpClientInstance.connect.mockRejectedValue(
+        new Error('Connection failed'),
+      );
+
+      // Need to await the async IIFE within discoverTools.
+      // Since discoverTools itself isn't async, we can't directly await it.
+      // We'll check the console.error mock.
+      toolRegistry.discoverTools();
+      await new Promise((resolve) => setTimeout(resolve, 100)); // Wait for async operations
+
+      expect(console.error).toHaveBeenCalledWith(
+        `failed to start or connect to MCP server 'failing-mcp' ${JSON.stringify({ command: 'fail-cmd' })}; \nError: Connection failed`,
+      );
+      expect(toolRegistry.getAllTools()).toHaveLength(0); // No tools should be registered
+    });
+  });
+});
+
+describe('DiscoveredTool', () => {
+  let config: Config;
+  const toolName = 'my-discovered-tool';
+  const toolDescription = 'Does something cool.';
+  const toolParamsSchema = {
+    type: 'object',
+    properties: { path: { type: 'string' } },
+  };
+  let mockSpawnInstance: Partial<ReturnType<typeof spawn>>;
+
+  beforeEach(() => {
+    const mockTargetDir = '/test/dir';
+    config = new Config(
+      'test-api-key',
+      'test-model',
+      false, // sandbox
+      mockTargetDir, // targetDir
+      false, // debugMode
+      undefined, // question
+      false, // fullContext
+      undefined, // toolDiscoveryCommand
+      undefined, // toolCallCommand
+      undefined, // mcpServerCommand
+      undefined, // mcpServers
+      'TestAgent/1.0', // userAgent
+    );
+    vi.spyOn(config, 'getToolDiscoveryCommand').mockReturnValue(
+      'discovery-cmd',
+    );
+    vi.spyOn(config, 'getToolCallCommand').mockReturnValue('call-cmd');
+
+    const mockStdin = {
+      write: vi.fn(),
+      end: vi.fn(),
+      on: vi.fn(),
+      writable: true,
+    } as any;
+
+    const mockStdout = {
+      on: vi.fn(),
+      read: vi.fn(),
+      readable: true,
+    } as any;
+
+    const mockStderr = {
+      on: vi.fn(),
+      read: vi.fn(),
+      readable: true,
+    } as any;
+
+    mockSpawnInstance = {
+      stdin: mockStdin,
+      stdout: mockStdout,
+      stderr: mockStderr,
+      on: vi.fn(), // For process events like 'close', 'error'
+      kill: vi.fn(),
+      pid: 123,
+      connected: true,
+      disconnect: vi.fn(),
+      ref: vi.fn(),
+      unref: vi.fn(),
+      spawnargs: [],
+      spawnfile: '',
+      channel: null,
+      exitCode: null,
+      signalCode: null,
+      killed: false,
+      stdio: [mockStdin, mockStdout, mockStderr, null, null] as any,
+    };
+    vi.mocked(spawn).mockReturnValue(mockSpawnInstance as any);
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it('constructor should set up properties correctly and enhance description', () => {
+    const tool = new DiscoveredTool(
+      config,
+      toolName,
+      toolDescription,
+      toolParamsSchema,
+    );
+    expect(tool.name).toBe(toolName);
+    expect(tool.schema.description).toContain(toolDescription);
+    expect(tool.schema.description).toContain('discovery-cmd');
+    expect(tool.schema.description).toContain('call-cmd my-discovered-tool');
+    expect(tool.schema.parameters).toEqual(toolParamsSchema);
+  });
+
+  it('execute should call spawn with correct command and params, and return stdout on success', async () => {
+    const tool = new DiscoveredTool(
+      config,
+      toolName,
+      toolDescription,
+      toolParamsSchema,
+    );
+    const params = { path: '/foo/bar' };
+    const expectedOutput = JSON.stringify({ result: 'success' });
+
+    // Simulate successful execution
+    (mockSpawnInstance.stdout!.on as Mocked<any>).mockImplementation(
+      (event: string, callback: (data: string) => void) => {
+        if (event === 'data') {
+          callback(expectedOutput);
+        }
+      },
+    );
+    (mockSpawnInstance.on as Mocked<any>).mockImplementation(
+      (
+        event: string,
+        callback: (code: number | null, signal: NodeJS.Signals | null) => void,
+      ) => {
+        if (event === 'close') {
+          callback(0, null); // Success
+        }
+      },
+    );
+
+    const result = await tool.execute(params);
+
+    expect(spawn).toHaveBeenCalledWith('call-cmd', [toolName]);
+    expect(mockSpawnInstance.stdin!.write).toHaveBeenCalledWith(
+      JSON.stringify(params),
+    );
+    expect(mockSpawnInstance.stdin!.end).toHaveBeenCalled();
+    expect(result.llmContent).toBe(expectedOutput);
+    expect(result.returnDisplay).toBe(expectedOutput);
+  });
+
+  it('execute should return error details if spawn results in an error', async () => {
+    const tool = new DiscoveredTool(
+      config,
+      toolName,
+      toolDescription,
+      toolParamsSchema,
+    );
+    const params = { path: '/foo/bar' };
+    const stderrOutput = 'Something went wrong';
+    const error = new Error('Spawn error');
+
+    // Simulate error during spawn
+    (mockSpawnInstance.stderr!.on as Mocked<any>).mockImplementation(
+      (event: string, callback: (data: string) => void) => {
+        if (event === 'data') {
+          callback(stderrOutput);
+        }
+      },
+    );
+    (mockSpawnInstance.on as Mocked<any>).mockImplementation(
+      (
+        event: string,
+        callback:
+          | ((code: number | null, signal: NodeJS.Signals | null) => void)
+          | ((error: Error) => void),
+      ) => {
+        if (event === 'error') {
+          (callback as (error: Error) => void)(error); // Simulate 'error' event
+        }
+        if (event === 'close') {
+          (
+            callback as (
+              code: number | null,
+              signal: NodeJS.Signals | null,
+            ) => void
+          )(1, null); // Non-zero exit code
+        }
+      },
+    );
+
+    const result = await tool.execute(params);
+
+    expect(result.llmContent).toContain(`Stderr: ${stderrOutput}`);
+    expect(result.llmContent).toContain(`Error: ${error.toString()}`);
+    expect(result.llmContent).toContain('Exit Code: 1');
+    expect(result.returnDisplay).toBe(result.llmContent);
+  });
+});
+
+describe('DiscoveredMCPTool', () => {
+  let config: Config;
+  let mockMcpClient: Client;
+  const toolName = 'my-mcp-tool';
+  const toolDescription = 'An MCP-discovered tool.';
+  const toolInputSchema = {
+    type: 'object',
+    properties: { data: { type: 'string' } },
+  };
+
+  beforeEach(() => {
+    const mockTargetDir = '/test/dir';
+    config = new Config(
+      'test-api-key',
+      'test-model',
+      false, // sandbox
+      mockTargetDir, // targetDir
+      false, // debugMode
+      undefined, // question
+      false, // fullContext
+      undefined, // toolDiscoveryCommand
+      undefined, // toolCallCommand
+      undefined, // mcpServerCommand
+      undefined, // mcpServers
+      'TestAgent/1.0', // userAgent
+    );
+    mockMcpClient = new Client({
+      name: 'test-client',
+      version: '0.0.0',
+    }) as Mocked<Client>;
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it('constructor should set up properties correctly and enhance description', () => {
+    const tool = new DiscoveredMCPTool(
+      mockMcpClient,
+      config,
+      toolName,
+      toolDescription,
+      toolInputSchema,
+    );
+    expect(tool.name).toBe(toolName);
+    expect(tool.schema.description).toContain(toolDescription);
+    expect(tool.schema.description).toContain('tools/call');
+    expect(tool.schema.description).toContain(toolName);
+    expect(tool.schema.parameters).toEqual(toolInputSchema);
+  });
+
+  it('execute should call mcpClient.callTool with correct params and return serialized result', async () => {
+    const tool = new DiscoveredMCPTool(
+      mockMcpClient,
+      config,
+      toolName,
+      toolDescription,
+      toolInputSchema,
+    );
+    const params = { data: 'test_data' };
+    const mcpResult = { success: true, value: 'processed' };
+
+    vi.mocked(mockMcpClient.callTool).mockResolvedValue(mcpResult);
+
+    const result = await tool.execute(params);
+
+    expect(mockMcpClient.callTool).toHaveBeenCalledWith({
+      name: toolName,
+      arguments: params,
+    });
+    const expectedOutput = JSON.stringify(mcpResult, null, 2);
+    expect(result.llmContent).toBe(expectedOutput);
+    expect(result.returnDisplay).toBe(expectedOutput);
+  });
+});
diff --git a/packages/server/src/tools/tool-registry.ts b/packages/server/src/tools/tool-registry.ts
index 67f47af0..83d5c329 100644
--- a/packages/server/src/tools/tool-registry.ts
+++ b/packages/server/src/tools/tool-registry.ts
@@ -209,7 +209,8 @@ export class ToolRegistry {
             `failed to start or connect to MCP server '${mcpServerName}' ` +
               `${JSON.stringify(mcpServer)}; \n${error}`,
           );
-          throw error;
+          // Do not re-throw, let other MCP servers be discovered.
+          return; // Exit this async IIFE if connection failed
         }
         mcpClient.onerror = (error) => {
           console.error('MCP ERROR', error.toString());