fix(server): exit when MCP client closes stdin pipe

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ElliotDrel

packages/server/src/server/stdio.ts

@@ -44,6 +44,11 @@ export class StdioServerTransport implements Transport {
             // Ignore errors during close — we're already in an error path
         });
     };
+    _onstdinclose = () => {
+        this.close().catch(() => {
+            // Ignore errors during close — stdin pipe ended
+        });
+    };
 
     /**
      * Starts listening for messages on `stdin`.
@@ -58,6 +63,7 @@ export class StdioServerTransport implements Transport {
         this._started = true;
         this._stdin.on('data', this._ondata);
         this._stdin.on('error', this._onerror);
+        this._stdin.on('close', this._onstdinclose);
         this._stdout.on('error', this._onstdouterror);
     }
 
@@ -85,6 +91,7 @@ export class StdioServerTransport implements Transport {
         // Remove our event listeners first
         this._stdin.off('data', this._ondata);
         this._stdin.off('error', this._onerror);
+        this._stdin.off('close', this._onstdinclose);
         this._stdout.off('error', this._onstdouterror);
 
         // Check if we were the only data listener

packages/server/test/server/stdio.test.ts

@@ -179,3 +179,46 @@ test('should fire onerror before onclose on stdout error', async () => {
 
     expect(events).toEqual(['error', 'close']);
 });
+
+test('should fire onclose when stdin emits close', async () => {
+    const server = new StdioServerTransport(input, output);
+    server.onerror = error => { throw error; };
+
+    let closeCount = 0;
+    server.onclose = () => { closeCount++; };
+
+    await server.start();
+    input.emit('close');
+
+    expect(closeCount).toBe(1);
+});
+
+test('should fire onclose when stdin emits end', async () => {
+    const server = new StdioServerTransport(input, output);
+    server.onerror = error => { throw error; };
+
+    let closeCount = 0;
+    server.onclose = () => { closeCount++; };
+
+    await server.start();
+    input.push(null); // signals end-of-stream
+
+    // Allow microtasks to flush
+    await new Promise(resolve => setTimeout(resolve, 0));
+
+    expect(closeCount).toBe(1);
+});
+
+test('should not fire onclose twice when close() called after stdin close', async () => {
+    const server = new StdioServerTransport(input, output);
+    server.onerror = () => {};
+
+    let closeCount = 0;
+    server.onclose = () => { closeCount++; };
+
+    await server.start();
+    input.emit('close');
+    await server.close();
+
+    expect(closeCount).toBe(1);
+});