feat: Session ID ASCII validation check (#206)

* Checks for session ASCII correctness

* tests: Session ID ASCII checks

src/scenarios/server/lifecycle.test.ts

@@ -0,0 +1,94 @@
+import { ServerInitializeScenario } from './lifecycle';
+import { connectToServer } from './client-helper';
+
+vi.mock('./client-helper', () => ({
+  connectToServer: vi.fn()
+}));
+
+describe('ServerInitializeScenario', () => {
+  const serverUrl = 'http://localhost:3000/mcp';
+  const closeMock = vi.fn().mockResolvedValue(undefined);
+  const fetchMock = vi.fn();
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+    vi.stubGlobal('fetch', fetchMock);
+    vi.mocked(connectToServer).mockResolvedValue({
+      client: {} as any,
+      close: closeMock
+    });
+  });
+
+  afterEach(() => {
+    vi.unstubAllGlobals();
+  });
+
+  it('returns INFO when the server does not provide an MCP-Session-Id header', async () => {
+    fetchMock.mockResolvedValue(new Response(null));
+
+    const checks = await new ServerInitializeScenario().run(serverUrl);
+
+    expect(connectToServer).toHaveBeenCalledWith(serverUrl);
+    expect(closeMock).toHaveBeenCalled();
+    expect(fetchMock).toHaveBeenCalledWith(
+      serverUrl,
+      expect.objectContaining({
+        method: 'POST'
+      })
+    );
+
+    expect(checks).toHaveLength(2);
+    expect(checks[0]?.id).toBe('server-initialize');
+    expect(checks[0]?.status).toBe('SUCCESS');
+    expect(checks[1]).toMatchObject({
+      id: 'server-session-id-visible-ascii',
+      status: 'INFO',
+      details: {
+        message:
+          'Server did not provide an MCP-Session-Id header (session ID is optional)'
+      }
+    });
+  });
+
+  it('returns SUCCESS when the server provides a visible ASCII session ID', async () => {
+    fetchMock.mockResolvedValue(
+      new Response(null, {
+        headers: {
+          'mcp-session-id': 'session-123_ABC'
+        }
+      })
+    );
+
+    const checks = await new ServerInitializeScenario().run(serverUrl);
+
+    expect(checks[1]).toMatchObject({
+      id: 'server-session-id-visible-ascii',
+      status: 'SUCCESS',
+      details: {
+        sessionId: 'session-123_ABC'
+      }
+    });
+  });
+
+  it('returns FAILURE when the server provides a non-ASCII session ID', async () => {
+    fetchMock.mockResolvedValue(
+      new Response(null, {
+        headers: {
+          'mcp-session-id': 'session-123-é'
+        }
+      })
+    );
+
+    const checks = await new ServerInitializeScenario().run(serverUrl);
+
+    expect(checks[1]).toMatchObject({
+      id: 'server-session-id-visible-ascii',
+      status: 'FAILURE',
+      errorMessage:
+        'Session ID contains characters outside visible ASCII range (0x21-0x7E)',
+      details: {
+        sessionId: 'session-123-é'
+      }
+    });
+  });
+});