fix: keep MCP stdio clean in specmatic-node

src/bin/__tests__/command.line.ts

@@ -112,3 +112,58 @@ test('handles empty JAVA_OPTS', async () => {
         }
     }
 });
+
+test('runs mcp server directly with inherited stdio', async () => {
+    mockSpawn.mockReturnValue(javaProcessMock);
+    jest.spyOn(fs, 'existsSync').mockReturnValue(true);
+
+    const originalExecutor = process.env.SPECMATIC_EXECUTOR;
+    delete process.env.SPECMATIC_EXECUTOR;
+
+    const consoleLogSpy = jest.spyOn(console, 'log').mockImplementation(() => undefined);
+
+    try {
+        callSpecmaticCli(['mcp', 'server']);
+        const specmaticJarPath = path.resolve(__dirname, '..', '..', '..', specmaticCoreJarName);
+
+        expect(mockSpawn.mock.calls[0][0]).toBe('java');
+        expect(mockSpawn.mock.calls[0][1]).toEqual(['-jar', path.resolve(specmaticJarPath), 'mcp', 'server']);
+        expect(mockSpawn.mock.calls[0][2]).toMatchObject({
+            stdio: 'inherit',
+            shell: false,
+            env: expect.objectContaining({
+                SPECMATIC_EXECUTOR: 'npm',
+            }),
+        });
+        expect(consoleLogSpy).not.toHaveBeenCalled();
+    } finally {
+        consoleLogSpy.mockRestore();
+        if (originalExecutor !== undefined) {
+            process.env.SPECMATIC_EXECUTOR = originalExecutor;
+        } else {
+            delete process.env.SPECMATIC_EXECUTOR;
+        }
+    }
+});
+
+test('runs mcp server directly when a root flag appears before it', async () => {
+    mockSpawn.mockReturnValue(javaProcessMock);
+    jest.spyOn(fs, 'existsSync').mockReturnValue(true);
+
+    const consoleLogSpy = jest.spyOn(console, 'log').mockImplementation(() => undefined);
+
+    try {
+        callSpecmaticCli(['--verbose', 'mcp', 'server']);
+        const specmaticJarPath = path.resolve(__dirname, '..', '..', '..', specmaticCoreJarName);
+
+        expect(mockSpawn.mock.calls[0][0]).toBe('java');
+        expect(mockSpawn.mock.calls[0][1]).toEqual(['-jar', path.resolve(specmaticJarPath), '--verbose', 'mcp', 'server']);
+        expect(mockSpawn.mock.calls[0][2]).toMatchObject({
+            stdio: 'inherit',
+            shell: false,
+        });
+        expect(consoleLogSpy).not.toHaveBeenCalled();
+    } finally {
+        consoleLogSpy.mockRestore();
+    }
+});

src/bin/command.line.ts

@@ -1,6 +1,37 @@
+import path from 'path';
+import { spawn } from 'child_process';
 import { parse } from 'shell-quote';
 import logger from '../common/logger'
 import { callCore} from '../common/runner'
+import { specmaticCoreJarName } from '../config';
+
+const getCommandPath = (args: string[]) => args.filter(arg => !arg.startsWith('-'));
+
+const isMcpServerCommand = (args: string[]) => {
+    const commandPath = getCommandPath(args);
+    return commandPath.length >= 2 && commandPath[0] === 'mcp' && commandPath[1] === 'server';
+};
+
+const callMcpServerDirectly = (args: string[], jvmArgs: string[]) => {
+    const rootPath = path.resolve(__dirname, '..', '..');
+    const specmaticJarPath = path.resolve(rootPath, specmaticCoreJarName);
+    const argsList: string[] = [...jvmArgs, '-jar', specmaticJarPath, ...args];
+    const envVars: NodeJS.ProcessEnv = { ...process.env };
+
+    if (!envVars['SPECMATIC_EXECUTOR']) {
+        envVars['SPECMATIC_EXECUTOR'] = 'npm';
+    }
+
+    const javaProcess = spawn('java', argsList, { stdio: 'inherit', shell: false, env: envVars });
+
+    javaProcess.on('error', () => {
+        process.exitCode = 1;
+    });
+
+    javaProcess.on('close', (code: number | null) => {
+        process.exitCode = code ?? 1;
+    });
+};
 
 const callSpecmaticCli = (argsv?: string[]) => {
     const args = argsv || process.argv.slice(2);
@@ -17,6 +48,11 @@ const callSpecmaticCli = (argsv?: string[]) => {
         }
     }
 
+    if (isMcpServerCommand(args)) {
+        callMcpServerDirectly(args, jvmArgs);
+        return;
+    }
+
     callCore(
         args,
         (err?: any) => {