fix: defects for token/retry/loading UX (#924)

## Summary
- tighten token rejection detection so non-token forbidden/policy
failures do not clear saved token or trigger token-recovery UX
- only show manual strategy-switch recovery when it is actionable
(faraday -> browserless)
- update converting-state copy to reflect actual behavior: result first,
preview after
- add regression coverage for non-token 403 behavior

## Scope
- Workstream B follow-up only
- no broad refactors

## Validation
- cd frontend && npm run test:unit -- --run src/__tests__/App.test.tsx

## Notes
- docs workspace in this environment has no git remote configured, so
only the html2rss-web PR is opened here.

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: gildesmarais

frontend/src/__tests__/App.test.tsx

@@ -276,7 +276,7 @@ describe('App', () => {
 
     expect(screen.getByText('Preparing feed')).toBeInTheDocument();
     expect(
-      screen.getByText('Creating the feed and loading its preview before showing the result.')
+      screen.getByText('Creating the feed now. The result appears first, then preview loading continues.')
     ).toBeInTheDocument();
   });
 
@@ -497,6 +497,37 @@ describe('App', () => {
     expect(screen.queryByRole('button', { name: /Try .* instead/ })).not.toBeInTheDocument();
   });
 
+  it('does not treat non-token forbidden failures as token rejection or strategy-recovery UX', async () => {
+    mockUseAccessToken.mockReturnValue({
+      token: 'saved-token',
+      hasToken: true,
+      saveToken: mockSaveToken,
+      clearToken: mockClearToken,
+      isLoading: false,
+      error: null,
+    });
+    mockConvertFeed.mockRejectedValueOnce(
+      Object.assign(new Error('URL not allowed for this account'), {
+        manualRetryStrategy: 'browserless',
+      })
+    );
+
+    render(<App />);
+
+    fireEvent.input(screen.getByLabelText('Page URL'), {
+      target: { value: 'https://example.com/articles' },
+    });
+    fireEvent.click(screen.getByRole('button', { name: 'Generate feed URL' }));
+
+    await screen.findByText('URL not allowed for this account');
+    expect(mockClearToken).not.toHaveBeenCalled();
+    expect(screen.queryByText('Add access token')).not.toBeInTheDocument();
+    expect(
+      screen.queryByText('Access token was rejected. Paste a valid token to continue.')
+    ).not.toBeInTheDocument();
+    expect(screen.queryByRole('button', { name: /Try .* instead/ })).not.toBeInTheDocument();
+  });
+
   it('shows the utility links in a user-focused order', () => {
     window.history.replaceState({}, '', 'http://localhost:3000/#result');
     render(<App />);

frontend/src/components/App.tsx

@@ -102,11 +102,36 @@ export function App() {
 
   const isAccessTokenError = (message: string) => {
     const normalized = message.toLowerCase();
+    const mentionsAuthToken =
+      normalized.includes('access token') ||
+      normalized.includes('token') ||
+      normalized.includes('authentication') ||
+      normalized.includes('bearer');
+
     return (
+      normalized.includes('unauthorized') ||
+      normalized.includes('invalid token') ||
+      normalized.includes('token rejected') ||
+      normalized.includes('authentication') ||
+      (normalized.includes('forbidden') && mentionsAuthToken)
+    );
+  };
+
+  const isActionableStrategySwitch = (message: string, currentStrategy: string, retryStrategy: string) => {
+    if (currentStrategy !== 'faraday' || retryStrategy !== 'browserless') return false;
+
+    const normalized = message.toLowerCase();
+    return !(
       normalized.includes('unauthorized') ||
       normalized.includes('forbidden') ||
+      normalized.includes('not allowed') ||
+      normalized.includes('disabled') ||
       normalized.includes('access token') ||
-      normalized.includes('authentication')
+      normalized.includes('token') ||
+      normalized.includes('authentication') ||
+      normalized.includes('bad request') ||
+      normalized.includes('url') ||
+      normalized.includes('unsupported strategy')
     );
   };
 
@@ -150,7 +175,9 @@ export function App() {
     } catch (submitError) {
       const message = submitError instanceof Error ? submitError.message : 'Unable to start feed generation.';
       const retryStrategy = (submitError as ConversionErrorWithMeta).manualRetryStrategy ?? '';
-      setManualRetryStrategy(retryStrategy);
+      setManualRetryStrategy(
+        isActionableStrategySwitch(message, strategy, retryStrategy) ? retryStrategy : ''
+      );
 
       if (feedCreation.access_token_required && isAccessTokenError(message)) {
         clearToken();

frontend/src/components/AppPanels.tsx

@@ -251,7 +251,7 @@ export function CreateFeedPanel({
       {isConverting && (
         <div class="ui-card ui-card--notice ui-card--padded notice" data-state="loading" role="status">
           <div class="notice__title">Preparing feed</div>
-          <p>Creating the feed and loading its preview before showing the result.</p>
+          <p>Creating the feed now. The result appears first, then preview loading continues.</p>
         </div>
       )}