Fall back to the structured Ask when a failed stream sent only whitespace

src/pages/AskPage.tsx

@@ -237,7 +237,6 @@ export default function AskPage() {
       const askStartTime = Date.now();
 
       if (!workspace.context && isAskStreamingSupported(config, { ...options, mode })) {
-        let receivedStreamText = false;
         let partialResponse = '';
         const streamingMessage = {
           // The stored reply reuses this id, so the bubble the user is reading never remounts.
@@ -258,7 +257,6 @@ export default function AskPage() {
           result = await streamAskChat(fullMessage, history, mode, config, options, {
             onDelta: (text) => {
               if (!isCurrentRequest()) return;
-              receivedStreamText = true;
               partialResponse += text;
               pendingText += text;
               if (!flushTimer) {
@@ -282,7 +280,9 @@ export default function AskPage() {
             // A newer request or Stop replaced this one; Stop keeps the partial itself.
             return true;
           }
-          if (receivedStreamText) {
+          // Whitespace alone is not an answer: a model that spent its cap on
+          // reasoning may send a newline first. Ask the structured endpoint then.
+          if (partialResponse.trim()) {
             toast({
               title: t('ask.streamInterrupted', 'Response was interrupted'),
               description: t('ask.streamInterruptedDesc', 'You can ask again to get a complete answer.'),

src/test/pages/AskStreamFallback.test.tsx

@@ -0,0 +1,65 @@
+import { fireEvent, render, screen, waitFor } from '@testing-library/react';
+import { MemoryRouter } from 'react-router-dom';
+import { describe, expect, it, vi } from 'vitest';
+
+Object.defineProperty(HTMLElement.prototype, 'scrollIntoView', { value: vi.fn(), writable: true });
+
+const mocks = vi.hoisted(() => ({
+  streamed: '',
+  askChat: vi.fn(),
+}));
+
+vi.mock('@/lib/supabase/AuthProvider', () => ({
+  useAuth: () => ({ user: { id: 'user-a' } }),
+}));
+
+vi.mock('@/lib/ai/client', async (importOriginal) => ({
+  ...(await importOriginal<typeof import('@/lib/ai/client')>()),
+  askChat: mocks.askChat,
+}));
+
+vi.mock('@/components/features/subscription', () => ({
+  LimitReachedModal: (): null => null,
+  ModelRestrictedModal: (): null => null,
+  PricingModal: (): null => null,
+}));
+
+// The stream sends `mocks.streamed`, then fails the way ai-stream does when
+// a reply is cut off at its cap before any real text.
+vi.mock('@/lib/ai/streaming', () => ({
+  isAskStreamingSupported: () => true,
+  streamAskChat: vi.fn(async (_message: string, _history: unknown, _mode: string, _config: unknown, _options: unknown, handlers: { onDelta: (text: string) => void }) => {
+    if (mocks.streamed) handlers.onDelta(mocks.streamed);
+    throw new Error('AI streaming failed. Please try again.');
+  }),
+}));
+
+import AskPage from '@/pages/AskPage';
+import { useSessionStore } from '@/lib/stores/session-store';
+import { enableOneOffMode } from '@/test/helpers/debate';
+
+async function ask(streamed: string) {
+  mocks.streamed = streamed;
+  mocks.askChat.mockReset();
+  mocks.askChat.mockResolvedValue({ response: 'Structured answer', followUpQuestions: [], uncertainties: [] });
+  enableOneOffMode();
+  useSessionStore.getState().clearAskMessages();
+  render(<MemoryRouter initialEntries={['/app/ask']}><AskPage /></MemoryRouter>);
+  fireEvent.change(screen.getByPlaceholderText('Ask your debate coach...'), { target: { value: 'How do I weigh cost?' } });
+  fireEvent.click(screen.getByRole('button', { name: 'Send message' }));
+  await waitFor(() => expect(useSessionStore.getState().askLoading).toBe(false));
+}
+
+describe('a failed Ask stream', () => {
+  it('asks the structured endpoint when the stream sent only whitespace', async () => {
+    await ask('\n\n');
+    expect(mocks.askChat).toHaveBeenCalledTimes(1);
+    expect(useSessionStore.getState().askMessages.at(-1)?.content).toBe('Structured answer');
+  });
+
+  it('keeps a partial answer instead of asking again', async () => {
+    await ask('Weigh access first');
+    expect(mocks.askChat).not.toHaveBeenCalled();
+    expect(useSessionStore.getState().askMessages.at(-1)?.content).toBe('Weigh access first');
+  });
+});