test: add regression test for provider manager Enter key handler

Structural verification that selectConfirm handler and onSetupAuth
callback exist in provider-manager.ts (#3579).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/tests/provider-manager-enter-key.test.ts

@@ -0,0 +1,46 @@
+/**
+ * Regression test for #3579 — Enter key initiates auth setup in provider manager
+ *
+ * The provider manager component did not handle the Enter key, leaving users
+ * unable to initiate auth setup without knowing the 'd' keyboard shortcut.
+ * The fix adds a selectConfirm handler that calls onSetupAuth.
+ *
+ * Structural verification test — reads source to confirm selectConfirm handler
+ * and onSetupAuth callback exist in provider-manager.ts.
+ */
+
+import { describe, test } from 'node:test';
+import assert from 'node:assert/strict';
+import { readFileSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import { dirname, join } from 'node:path';
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = dirname(__filename);
+
+const source = readFileSync(
+  join(__dirname, '..', '..', 'packages', 'pi-coding-agent', 'src', 'modes', 'interactive', 'components', 'provider-manager.ts'),
+  'utf-8',
+);
+
+describe('provider manager Enter key handler (#3579)', () => {
+  test('onSetupAuth callback property exists', () => {
+    assert.match(source, /onSetupAuth/,
+      'onSetupAuth callback should be defined');
+  });
+
+  test('selectConfirm key handler exists', () => {
+    assert.match(source, /selectConfirm/,
+      'selectConfirm key binding should be handled');
+  });
+
+  test('onSetupAuth is called with provider name', () => {
+    assert.match(source, /this\.onSetupAuth\(provider\.name\)/,
+      'onSetupAuth should be called with provider.name');
+  });
+
+  test('setup auth hint is shown', () => {
+    assert.match(source, /setup auth/,
+      'enter key hint should mention "setup auth"');
+  });
+});