diff --git a/src/completion.test.ts b/src/completion.test.ts
new file mode 100644
index 00000000..415dc4c5
--- /dev/null
+++ b/src/completion.test.ts
@@ -0,0 +1,30 @@
+import { describe, expect, it, vi } from 'vitest';
+
+const { mockGetRegistry } = vi.hoisted(() => ({
+  mockGetRegistry: vi.fn(() => new Map([
+    ['github/issues', { site: 'github', name: 'issues' }],
+  ])),
+}));
+
+vi.mock('./registry.js', () => ({
+  getRegistry: mockGetRegistry,
+}));
+
+import { getCompletions } from './completion.js';
+
+describe('getCompletions', () => {
+  it('includes top-level built-ins that are registered outside the site registry', () => {
+    const completions = getCompletions([], 1);
+
+    expect(completions).toContain('plugin');
+    expect(completions).toContain('install');
+    expect(completions).toContain('register');
+    expect(completions).not.toContain('setup');
+  });
+
+  it('still includes discovered site names', () => {
+    const completions = getCompletions([], 1);
+
+    expect(completions).toContain('github');
+  });
+});
diff --git a/src/completion.ts b/src/completion.ts
index 00c031ae..9b58e29c 100644
--- a/src/completion.ts
+++ b/src/completion.ts
@@ -24,7 +24,9 @@ const BUILTIN_COMMANDS = [
   'generate',
   'cascade',
   'doctor',
-  'setup',
+  'plugin',
+  'install',
+  'register',
   'completion',
 ];