fix(recover): wrap embedded-manifest atob in try/catch for corrupt base64

atob() throws DOMException when its input isn't valid base64. The
embedded manifest lives in recover.html, which is meant to be archived
long-term; bit rot, truncated copies, or storage degradation can leave
the base64 payload unreadable. Previously the exception propagated,
leaving Step 2 asking the user to load MANIFEST.age manually — but the
whole point of embedding was to avoid needing the separate file.

Catch the decode failure and surface a toast so the user knows their
copy of recover.html is damaged and to try another copy. The i18n
function t() already falls back to English when a locale is missing
translations, so the three new keys work across all languages even
before translators catch up.

Fixes #107

Author: tmchow

internal/html/assets/src/app.ts

@@ -341,13 +341,27 @@ type UIShare = ParsedShare & { isHolder?: boolean };
 
     // Load embedded manifest if available (included when MANIFEST.age is small enough)
     if (personalization.manifestB64) {
-      const binary = atob(personalization.manifestB64);
-      const bytes = new Uint8Array(binary.length);
-      for (let i = 0; i < binary.length; i++) {
-        bytes[i] = binary.charCodeAt(i);
+      try {
+        const binary = atob(personalization.manifestB64);
+        const bytes = new Uint8Array(binary.length);
+        for (let i = 0; i < binary.length; i++) {
+          bytes[i] = binary.charCodeAt(i);
+        }
+        state.manifest = bytes;
+        showManifestLoaded('MANIFEST.age', state.manifest.length, 'embedded');
+      } catch (err) {
+        // atob throws DOMException on corrupt base64 (bit rot, truncated copy,
+        // storage degradation). Surface it so the user knows to try another
+        // copy of recover.html rather than assuming they need MANIFEST.age
+        // separately.
+        showError(
+          t('error_corrupt_embedded_manifest_message'),
+          {
+            title: t('error_corrupt_embedded_manifest_title'),
+            guidance: t('error_corrupt_embedded_manifest_guidance'),
+          }
+        );
       }
-      state.manifest = bytes;
-      showManifestLoaded('MANIFEST.age', state.manifest.length, 'embedded');
     }
 
     checkRecoverReady();

internal/translations/recover/en.json

@@ -77,6 +77,9 @@
   "error_extract_status": "Extraction failed. The archive may be corrupted.",
   "error_recovery_title": "Recovery failed",
   "error_recovery_guidance": "Check that you have the correct pieces and the right MANIFEST.age file. You can try again with different pieces.",
+  "error_corrupt_embedded_manifest_title": "Corrupted embedded archive",
+  "error_corrupt_embedded_manifest_message": "The archive embedded in this recover.html is damaged and couldn't be loaded.",
+  "error_corrupt_embedded_manifest_guidance": "Your copy of recover.html may be truncated or corrupted. Try another copy of the file, or load MANIFEST.age manually in Step 2.",
   "action_reload": "Reload page",
   "action_use_cli": "Use CLI tool",
   "action_try_different_shares": "Try different pieces",