Detect backend down (#5010)

# Description of Changes

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- What was changed
- Why the change was made
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Closes #(issue_number)
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## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

frontend/src/core/services/httpErrorHandler.ts

@@ -88,6 +88,7 @@ const SPECIAL_SUPPRESS_MS = 1500; // brief window to suppress generic duplicate
  * Returns true if the error should be suppressed (deduplicated), false otherwise
  */
 export async function handleHttpError(error: any): Promise<boolean> {
+  const skipAuthRedirect = error?.config?.skipAuthRedirect === true;
   // Check if this error should skip the global toast (component will handle it)
   if (error?.config?.suppressErrorToast === true) {
     return false; // Don't show global toast, but continue rejection
@@ -105,12 +106,19 @@ export async function handleHttpError(error: any): Promise<boolean> {
                       pathname.includes('/invite/');
 
     // If not on auth page, redirect to login with expired session message
-    if (!isAuthPage) {
+    if (!isAuthPage && !skipAuthRedirect) {
       console.debug('[httpErrorHandler] 401 detected, redirecting to login');
       // Store the current location so we can redirect back after login
       const currentLocation = window.location.pathname + window.location.search;
-      // Redirect to login with state
-      window.location.href = `/login?expired=true&from=${encodeURIComponent(currentLocation)}`;
+      // Redirect to login with state (only show expired when a JWT existed)
+      let hadStoredJwt = false;
+      try {
+        hadStoredJwt = Boolean(localStorage.getItem('stirling_jwt'));
+      } catch {
+        // ignore storage access failures
+      }
+      const expiredPrefix = hadStoredJwt ? 'expired=true&' : '';
+      window.location.href = `/login?${expiredPrefix}from=${encodeURIComponent(currentLocation)}`;
       return true; // Suppress toast since we're redirecting
     }
 
@@ -173,4 +181,4 @@ export async function handleHttpError(error: any): Promise<boolean> {
   }
 
   return false; // Error was handled with toast, continue normal rejection
-}
+}