feat: add MCP Runtime Server Plugin (plugin-mcp-server)

CHANGELOG.md

@@ -7,6 +7,26 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- **MCP Runtime Server Plugin (`plugin-mcp-server`)** — New kernel plugin that exposes ObjectStack
+  as a Model Context Protocol (MCP) server for external AI clients (Claude Desktop, Cursor, VS Code
+  Copilot, etc.). Features include:
+  - **Tool Bridge**: All registered AI tools from `ToolRegistry` (9 built-in tools: `list_objects`,
+    `describe_object`, `query_records`, `get_record`, `aggregate_data`, `create_object`, `add_field`,
+    `modify_field`, `delete_field`) are automatically exposed as MCP tools with correct annotations
+    (readOnlyHint, destructiveHint).
+  - **Resource Bridge**: Object schemas (`objectstack://objects/{objectName}`), object list
+    (`objectstack://objects`), record access (`objectstack://objects/{objectName}/records/{recordId}`),
+    and metadata types (`objectstack://metadata/types`) exposed as MCP resources.
+  - **Prompt Bridge**: Registered agents (`data_chat`, `metadata_assistant`, etc.) exposed as MCP
+    prompts with context arguments (objectName, recordId, viewName).
+  - **Transport**: stdio transport via `@modelcontextprotocol/sdk` for local AI client integration.
+  - **Environment Configuration**: `MCP_SERVER_ENABLED=true` to auto-start, `MCP_SERVER_NAME` and
+    `MCP_SERVER_TRANSPORT` for customization.
+  - **Extensibility**: `mcp:ready` kernel hook allows other plugins to extend the MCP server.
+  - Studio frontend AI interface remains unchanged — it continues to use REST/SSE via
+    Vercel Data Stream Protocol.
+
 ### Changed
 - **Unified `list_objects` / `describe_object` tools (`service-ai`)** — Merged the duplicate
   `list_metadata_objects` → `list_objects` and `describe_metadata_object` → `describe_object`

packages/plugins/plugin-mcp-server/package.json

@@ -0,0 +1,31 @@
+{
+  "name": "@objectstack/plugin-mcp-server",
+  "version": "4.0.2",
+  "license": "Apache-2.0",
+  "description": "MCP Runtime Server Plugin for ObjectStack — exposes AI tools, data resources, and agent prompts via the Model Context Protocol",
+  "type": "module",
+  "main": "dist/index.js",
+  "types": "dist/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./dist/index.d.ts",
+      "import": "./dist/index.js",
+      "require": "./dist/index.cjs"
+    }
+  },
+  "scripts": {
+    "build": "tsup --config ../../../tsup.config.ts",
+    "test": "vitest run"
+  },
+  "dependencies": {
+    "@modelcontextprotocol/sdk": "^1.29.0",
+    "@objectstack/core": "workspace:*",
+    "@objectstack/spec": "workspace:*",
+    "zod": "^4.3.6"
+  },
+  "devDependencies": {
+    "@types/node": "^25.5.2",
+    "typescript": "^6.0.2",
+    "vitest": "^4.1.2"
+  }
+}

packages/plugins/plugin-mcp-server/src/__tests__/mcp-server-runtime.test.ts

@@ -0,0 +1,279 @@
+// Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
+
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { MCPServerRuntime } from '../mcp-server-runtime.js';
+import type { MCPServerRuntimeConfig } from '../mcp-server-runtime.js';
+import type { AIToolDefinition, ToolCallPart } from '@objectstack/spec/contracts';
+import type { ToolRegistry, ToolExecutionResult } from '../types.js';
+
+// ---------------------------------------------------------------------------
+// Mock helpers
+// ---------------------------------------------------------------------------
+
+function createMockToolRegistry(tools: AIToolDefinition[] = []): ToolRegistry {
+  const handlers = new Map<string, (args: Record<string, unknown>) => Promise<string>>();
+
+  return {
+    getAll: () => tools,
+    execute: vi.fn(async (toolCall: ToolCallPart): Promise<ToolExecutionResult> => {
+      const handler = handlers.get(toolCall.toolName);
+      if (!handler) {
+        return {
+          type: 'tool-result',
+          toolCallId: toolCall.toolCallId,
+          toolName: toolCall.toolName,
+          output: { type: 'text', value: `Tool "${toolCall.toolName}" not found` },
+          isError: true,
+        };
+      }
+      const args = typeof toolCall.input === 'string'
+        ? JSON.parse(toolCall.input)
+        : (toolCall.input as Record<string, unknown>) ?? {};
+      const content = await handler(args);
+      return {
+        type: 'tool-result',
+        toolCallId: toolCall.toolCallId,
+        toolName: toolCall.toolName,
+        output: { type: 'text', value: content },
+      };
+    }),
+    // Expose for test setup
+    _setHandler: (name: string, fn: (args: Record<string, unknown>) => Promise<string>) => {
+      handlers.set(name, fn);
+    },
+  } as ToolRegistry & { _setHandler: (name: string, fn: any) => void };
+}
+
+function createMockMetadataService() {
+  const objects: Record<string, any> = {
+    account: {
+      name: 'account',
+      label: 'Account',
+      fields: {
+        name: { type: 'text', label: 'Name', required: true },
+        email: { type: 'email', label: 'Email' },
+        status: { type: 'select', label: 'Status' },
+      },
+      enable: { softDelete: true },
+    },
+    contact: {
+      name: 'contact',
+      label: 'Contact',
+      fields: {
+        first_name: { type: 'text', label: 'First Name', required: true },
+        last_name: { type: 'text', label: 'Last Name', required: true },
+      },
+    },
+  };
+
+  const agents: Record<string, any> = {
+    data_chat: {
+      name: 'data_chat',
+      label: 'Data Assistant',
+      role: 'Business Data Analyst',
+      instructions: 'You are a helpful data assistant.',
+      active: true,
+    },
+    metadata_assistant: {
+      name: 'metadata_assistant',
+      label: 'Metadata Assistant',
+      role: 'Schema Designer',
+      instructions: 'You help design data schemas.',
+      active: true,
+    },
+  };
+
+  return {
+    listObjects: vi.fn(async () => Object.values(objects)),
+    getObject: vi.fn(async (name: string) => objects[name] ?? null),
+    get: vi.fn(async (type: string, name: string) => {
+      if (type === 'agent') return agents[name] ?? null;
+      return null;
+    }),
+    list: vi.fn(async (type: string) => {
+      if (type === 'agent') return Object.values(agents);
+      return [];
+    }),
+    exists: vi.fn(async (type: string, name: string) => {
+      if (type === 'agent') return name in agents;
+      return false;
+    }),
+    getRegisteredTypes: vi.fn(async () => ['object', 'app', 'view', 'agent', 'tool']),
+    register: vi.fn(),
+    unregister: vi.fn(),
+  };
+}
+
+function createMockDataEngine() {
+  const records: Record<string, Record<string, any>> = {
+    'account:abc123': { id: 'abc123', name: 'Acme Corp', status: 'active' },
+    'contact:xyz789': { id: 'xyz789', first_name: 'John', last_name: 'Doe' },
+  };
+
+  return {
+    find: vi.fn(async () => []),
+    findOne: vi.fn(async (objectName: string, options: any) => {
+      const recordId = options?.where?.id;
+      return records[`${objectName}:${recordId}`] ?? null;
+    }),
+    insert: vi.fn(),
+    update: vi.fn(),
+    delete: vi.fn(),
+    count: vi.fn(async () => 0),
+    aggregate: vi.fn(async () => []),
+  };
+}
+
+function createMockLogger() {
+  return {
+    info: vi.fn(),
+    warn: vi.fn(),
+    error: vi.fn(),
+    debug: vi.fn(),
+  };
+}
+
+// ---------------------------------------------------------------------------
+// Tests
+// ---------------------------------------------------------------------------
+
+describe('MCPServerRuntime', () => {
+  let runtime: MCPServerRuntime;
+  let mockLogger: ReturnType<typeof createMockLogger>;
+
+  beforeEach(() => {
+    mockLogger = createMockLogger();
+    runtime = new MCPServerRuntime({
+      name: 'test-objectstack',
+      version: '1.0.0-test',
+      logger: mockLogger as any,
+    });
+  });
+
+  describe('constructor', () => {
+    it('should create with default config', () => {
+      const defaultRuntime = new MCPServerRuntime();
+      expect(defaultRuntime).toBeDefined();
+      expect(defaultRuntime.isStarted).toBe(false);
+    });
+
+    it('should create with custom config', () => {
+      expect(runtime).toBeDefined();
+      expect(runtime.isStarted).toBe(false);
+    });
+
+    it('should expose the underlying McpServer', () => {
+      expect(runtime.server).toBeDefined();
+    });
+  });
+
+  describe('bridgeTools', () => {
+    it('should bridge all tools from ToolRegistry', () => {
+      const tools: AIToolDefinition[] = [
+        {
+          name: 'list_objects',
+          description: 'List all objects',
+          parameters: { type: 'object', properties: {} },
+        },
+        {
+          name: 'query_records',
+          description: 'Query records',
+          parameters: { type: 'object', properties: { objectName: { type: 'string' } }, required: ['objectName'] },
+        },
+      ];
+
+      const registry = createMockToolRegistry(tools);
+      runtime.bridgeTools(registry);
+
+      expect(mockLogger.info).toHaveBeenCalledWith('[MCP] Bridged 2 tools from ToolRegistry');
+    });
+
+    it('should bridge zero tools gracefully', () => {
+      const registry = createMockToolRegistry([]);
+      runtime.bridgeTools(registry);
+
+      expect(mockLogger.info).toHaveBeenCalledWith('[MCP] Bridged 0 tools from ToolRegistry');
+    });
+
+    it('should bridge all 9 standard tools', () => {
+      const standardTools: AIToolDefinition[] = [
+        { name: 'create_object', description: 'Create object', parameters: {} },
+        { name: 'add_field', description: 'Add field', parameters: {} },
+        { name: 'modify_field', description: 'Modify field', parameters: {} },
+        { name: 'delete_field', description: 'Delete field', parameters: {} },
+        { name: 'list_objects', description: 'List objects', parameters: {} },
+        { name: 'describe_object', description: 'Describe object', parameters: {} },
+        { name: 'query_records', description: 'Query records', parameters: {} },
+        { name: 'get_record', description: 'Get record', parameters: {} },
+        { name: 'aggregate_data', description: 'Aggregate data', parameters: {} },
+      ];
+
+      const registry = createMockToolRegistry(standardTools);
+      runtime.bridgeTools(registry);
+
+      expect(mockLogger.info).toHaveBeenCalledWith('[MCP] Bridged 9 tools from ToolRegistry');
+    });
+  });
+
+  describe('bridgeResources', () => {
+    it('should bridge metadata resources', () => {
+      const metadataService = createMockMetadataService();
+      runtime.bridgeResources(metadataService as any);
+
+      // Should register: object_list, object_schema, metadata_types (3 resources, no dataEngine = no record_by_id)
+      expect(mockLogger.info).toHaveBeenCalledWith('[MCP] Bridged 3 resource endpoints');
+    });
+
+    it('should bridge record resources when DataEngine is available', () => {
+      const metadataService = createMockMetadataService();
+      const dataEngine = createMockDataEngine();
+      runtime.bridgeResources(metadataService as any, dataEngine as any);
+
+      // Should register: object_list, object_schema, record_by_id, metadata_types (4 resources)
+      expect(mockLogger.info).toHaveBeenCalledWith('[MCP] Bridged 4 resource endpoints');
+    });
+
+    it('should skip metadata_types when getRegisteredTypes is not available', () => {
+      const metadataService = createMockMetadataService();
+      delete (metadataService as any).getRegisteredTypes;
+      runtime.bridgeResources(metadataService as any);
+
+      // Should register: object_list, object_schema only (2 resources)
+      expect(mockLogger.info).toHaveBeenCalledWith('[MCP] Bridged 2 resource endpoints');
+    });
+  });
+
+  describe('bridgePrompts', () => {
+    it('should register agent prompt', () => {
+      const metadataService = createMockMetadataService();
+      runtime.bridgePrompts(metadataService as any);
+
+      expect(mockLogger.info).toHaveBeenCalledWith('[MCP] Agent prompts bridged');
+    });
+  });
+
+  describe('lifecycle', () => {
+    it('should not be started initially', () => {
+      expect(runtime.isStarted).toBe(false);
+    });
+
+    it('should warn when HTTP transport is requested', async () => {
+      const httpRuntime = new MCPServerRuntime({
+        transport: 'http',
+        logger: mockLogger as any,
+      });
+
+      await httpRuntime.start();
+
+      expect(httpRuntime.isStarted).toBe(false);
+      expect(mockLogger.warn).toHaveBeenCalledWith(
+        '[MCP] HTTP transport is not yet supported. Use stdio transport.',
+      );
+    });
+
+    it('should be idempotent on stop when not started', async () => {
+      await runtime.stop();
+      expect(runtime.isStarted).toBe(false);
+    });
+  });
+});