diff --git a/packages/ui/src/lib/persistence.test.ts b/packages/ui/src/lib/persistence.test.ts
index 38057e9c..bd59bcfe 100644
--- a/packages/ui/src/lib/persistence.test.ts
+++ b/packages/ui/src/lib/persistence.test.ts
@@ -241,6 +241,47 @@ describe('updateDesktopSettings', () => {
     }
   });
 
+  test('sanitizes a successful fallback settings response before applying it', async () => {
+    const previousFetch = globalThis.fetch;
+    const fallbackFetch: typeof fetch = async () => new Response(JSON.stringify({ terminalShell: 'zsh' }), {
+      headers: { 'Content-Type': 'application/json' },
+    });
+    try {
+      globalThis.fetch = fallbackFetch;
+      useUIStore.getState().setTerminalShell('fish');
+
+      await updateDesktopSettings({ terminalShell: 'zsh' });
+
+      expect(useUIStore.getState().terminalShell).toBe('zsh');
+      expect(getSettingsSaveState()).toBe('idle');
+    } finally {
+      globalThis.fetch = previousFetch;
+    }
+  });
+
+  test('reports an error without applying a malformed fallback settings response', async () => {
+    const previousFetch = globalThis.fetch;
+    const fallbackFetch: typeof fetch = async () => new Response(JSON.stringify('ok'), {
+      headers: { 'Content-Type': 'application/json' },
+    });
+    const states: string[] = [];
+    const unsubscribe = subscribeToSettingsSaveState(() => {
+      states.push(getSettingsSaveState());
+    });
+    try {
+      globalThis.fetch = fallbackFetch;
+      useUIStore.getState().setTerminalShell('fish');
+
+      await updateDesktopSettings({ terminalShell: 'zsh' });
+
+      expect(useUIStore.getState().terminalShell).toBe('fish');
+      expect(states).toEqual(['saving', 'error']);
+    } finally {
+      unsubscribe();
+      globalThis.fetch = previousFetch;
+    }
+  });
+
   test('drains a pending save to the previous runtime and ignores its stale response', async () => {
     switchRuntimeEndpoint({ apiBaseUrl: 'https://settings-a.example', runtimeKey: 'settings-a' });
     const saveResult = deferred<SettingsPayload>();
diff --git a/packages/ui/src/lib/persistence.ts b/packages/ui/src/lib/persistence.ts
index c02fc88d..c53c4c4c 100644
--- a/packages/ui/src/lib/persistence.ts
+++ b/packages/ui/src/lib/persistence.ts
@@ -130,7 +130,7 @@ const persistToLocalStorage = (settings: DesktopSettings) => {
 
   if (Array.isArray(settings.projects) && settings.projects.length > 0) {
     const collapsed = settings.projects
-      .filter((project) => (project as unknown as { sidebarCollapsed?: boolean }).sidebarCollapsed === true)
+      .filter((project) => project.sidebarCollapsed === true)
       .map((project) => project.id)
       .filter((id): id is string => typeof id === 'string' && id.length > 0);
     if (collapsed.length > 0) {
@@ -273,13 +273,14 @@ const sanitizeSkillCatalogs = (value: unknown): DesktopSettings['skillCatalogs']
     if (seen.has(id)) continue;
     seen.add(id);
 
-    result.push({
+    const catalog: NonNullable<DesktopSettings['skillCatalogs']>[number] = {
       id,
       label,
       source,
-      ...(subpath ? { subpath } : {}),
-      ...(gitIdentityId ? { gitIdentityId } : {}),
-    });
+    };
+    if (subpath) catalog.subpath = subpath;
+    if (gitIdentityId) catalog.gitIdentityId = gitIdentityId;
+    result.push(catalog);
   }
 
   return result;
@@ -393,7 +394,7 @@ const sanitizeProjects = (value: unknown): DesktopSettings['projects'] | undefin
       project.icon = candidate.icon.trim();
     }
     if (candidate.iconImage === null) {
-      (project as unknown as Record<string, unknown>).iconImage = null;
+      project.iconImage = null;
     } else if (candidate.iconImage && typeof candidate.iconImage === 'object') {
       const iconImage = candidate.iconImage as Record<string, unknown>;
       const mime = typeof iconImage.mime === 'string' ? iconImage.mime.trim() : '';
@@ -404,18 +405,18 @@ const sanitizeProjects = (value: unknown): DesktopSettings['projects'] | undefin
         ? iconImage.source
         : null;
       if (mime && updatedAt > 0 && source) {
-        (project as unknown as Record<string, unknown>).iconImage = { mime, updatedAt, source };
+        project.iconImage = { mime, updatedAt, source };
       }
     }
     if (typeof candidate.color === 'string' && candidate.color.trim().length > 0) {
       project.color = candidate.color.trim();
     }
     if (candidate.iconBackground === null) {
-      (project as unknown as Record<string, unknown>).iconBackground = null;
+      project.iconBackground = null;
     } else {
       const iconBackground = normalizeIconBackground(candidate.iconBackground);
       if (iconBackground) {
-        (project as unknown as Record<string, unknown>).iconBackground = iconBackground;
+        project.iconBackground = iconBackground;
       }
     }
     if (typeof candidate.addedAt === 'number' && Number.isFinite(candidate.addedAt) && candidate.addedAt >= 0) {
@@ -429,7 +430,7 @@ const sanitizeProjects = (value: unknown): DesktopSettings['projects'] | undefin
       project.lastOpenedAt = candidate.lastOpenedAt;
     }
     if (typeof candidate.sidebarCollapsed === 'boolean') {
-      (project as unknown as Record<string, unknown>).sidebarCollapsed = candidate.sidebarCollapsed;
+      project.sidebarCollapsed = candidate.sidebarCollapsed;
     }
     result.push(project);
   }
@@ -507,7 +508,7 @@ const sanitizeModelRefs = (value: unknown, limit: number): Array<{ providerID: s
 };
 
 const getPersistApi = (): PersistApi | undefined => {
-  const candidate = (useUIStore as unknown as { persist?: PersistApi }).persist;
+  const candidate = useUIStore.persist;
   if (candidate && typeof candidate === 'object') {
     return candidate;
   }
@@ -1325,11 +1326,7 @@ const sanitizeWebSettings = (payload: unknown): DesktopSettings | null => {
     for (const [providerId, config] of Object.entries(candidate.usageModelGroups)) {
       if (config && typeof config === 'object') {
         const typedConfig = config as Record<string, unknown>;
-        const providerConfig: {
-          customGroups?: Array<{id: string; label: string; models: string[]; order: number}>;
-          modelAssignments?: Record<string, string>;
-          renamedGroups?: Record<string, string>;
-        } = {};
+        const providerConfig: NonNullable<DesktopSettings['usageModelGroups']>[string] = {};
 
         // Parse customGroups
         if (Array.isArray(typedConfig.customGroups)) {
@@ -1875,7 +1872,7 @@ async function _flushSettingsUpdate(): Promise<void> {
         return;
       }
 
-      const updated = (await response.json().catch(() => null)) as DesktopSettings | null;
+      const updated = sanitizeWebSettings(await response.json().catch(() => null));
       if (!isSettingsRuntimeContextCurrent(context)) return;
       if (updated) {
         applyDesktopUiPreferences(updated);