fix: expand paste placeholders in TextInput on submit (#19946)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

packages/cli/src/ui/components/AskUserDialog.test.tsx

@@ -1347,4 +1347,47 @@ describe('AskUserDialog', () => {
       });
     });
   });
+
+  it('expands paste placeholders in multi-select custom option via Done', async () => {
+    const questions: Question[] = [
+      {
+        question: 'Which features?',
+        header: 'Features',
+        type: QuestionType.CHOICE,
+        options: [{ label: 'TypeScript', description: '' }],
+        multiSelect: true,
+      },
+    ];
+
+    const onSubmit = vi.fn();
+    const { stdin } = renderWithProviders(
+      <AskUserDialog
+        questions={questions}
+        onSubmit={onSubmit}
+        onCancel={vi.fn()}
+        width={120}
+      />,
+      { width: 120 },
+    );
+
+    // Select TypeScript
+    writeKey(stdin, '\r');
+    // Down to Other
+    writeKey(stdin, '\x1b[B');
+
+    // Simulate bracketed paste of multi-line text into the custom option
+    const pastedText = 'Line 1\nLine 2\nLine 3\nLine 4\nLine 5\nLine 6';
+    const ESC = '\x1b';
+    writeKey(stdin, `${ESC}[200~${pastedText}${ESC}[201~`);
+
+    // Down to Done and submit
+    writeKey(stdin, '\x1b[B');
+    writeKey(stdin, '\r');
+
+    await waitFor(() => {
+      expect(onSubmit).toHaveBeenCalledWith({
+        '0': `TypeScript, ${pastedText}`,
+      });
+    });
+  });
 });