fix: show desktop update errors

src/app/pages/client/DesktopUpdater.test.tsx

@@ -2,7 +2,7 @@ import { render, screen, fireEvent, waitFor } from '@testing-library/react';
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 import { useAtomValue, useSetAtom, Provider } from 'jotai';
 import { globalBannersAtom } from '$state/globalBanners';
-import { triggerUpdateCheckAtom } from '$state/desktopUpdate';
+import { triggerUpdateCheckAtom, updatePhaseAtom } from '$state/desktopUpdate';
 import { DesktopUpdatePill } from '$components/tauri/DesktopUpdatePill';
 import { DesktopUpdater } from './DesktopUpdater';
 
@@ -32,6 +32,7 @@ function BannersProbe() {
       {banners.map((b) => (
         <section key={b.id} data-testid={`banner-${b.id}`}>
           <span>{b.title}</span>
+          <span>{b.description}</span>
           <button type="button" onClick={b.primaryAction.onClick}>
             {b.primaryAction.label}
           </button>
@@ -55,6 +56,11 @@ function CheckNowButton() {
   );
 }
 
+function UpdatePhaseProbe() {
+  const phase = useAtomValue(updatePhaseAtom);
+  return <output data-testid="update-phase">{phase.type}</output>;
+}
+
 function makeUpdate(version: string) {
   return {
     version,
@@ -166,6 +172,7 @@ describe('DesktopUpdater', () => {
         <DesktopUpdatePill />
         <DesktopUpdater />
         <BannersProbe />
+        <UpdatePhaseProbe />
       </Provider>
     );
 
@@ -176,10 +183,12 @@ describe('DesktopUpdater', () => {
     fireEvent.click(screen.getByRole('button', { name: 'Download & Install' }));
     await waitFor(() => expect(update.downloadAndInstall).toHaveBeenCalledTimes(1));
     await waitFor(() => {
-      expect(screen.getByRole('button', { name: 'Download & Install' })).toBeInTheDocument();
+      expect(screen.getByText('Update Failed')).toBeInTheDocument();
     });
+    expect(screen.getByText('eacces')).toBeInTheDocument();
+    expect(screen.getByTestId('update-phase')).toHaveTextContent('ready');
 
-    fireEvent.click(screen.getByRole('button', { name: 'Download & Install' }));
+    fireEvent.click(screen.getByRole('button', { name: 'Retry' }));
     await waitFor(() => expect(update.downloadAndInstall).toHaveBeenCalledTimes(2));
     await screen.findByTestId('banner-desktop-update-restart');
   });

src/app/pages/client/DesktopUpdater.tsx

@@ -29,6 +29,7 @@ export function DesktopUpdater() {
   const [isDownloading, setIsDownloading] = useState(false);
   const [isInstalled, setIsInstalled] = useState(false);
   const [isInstalling, setIsInstalling] = useState(false);
+  const [installError, setInstallError] = useState<string | null>(null);
   const [dismissed, setDismissed] = useState(false);
   const [useCustomTitleBar] = useDesktopSetting('useCustomTitleBar');
   const hasUpdateRef = useRef(false);
@@ -145,6 +146,7 @@ export function DesktopUpdater() {
     if (!updateInfo || installStartedRef.current) return;
     installStartedRef.current = true;
     try {
+      setInstallError(null);
       setIsDownloading(true);
       setPhase({ type: 'downloading', progress: 0 });
 
@@ -180,8 +182,10 @@ export function DesktopUpdater() {
       closePendingUpdate(updateInfo);
     } catch (err) {
       log.error('Failed to install update', err);
+      setInstallError(err instanceof Error ? err.message : String(err));
       setIsDownloading(false);
       setIsInstalling(false);
+      setPhase({ type: 'ready', version: updateInfo.version });
       installStartedRef.current = false;
     }
   }, [closePendingUpdate, updateInfo, setPhase]);
@@ -223,6 +227,26 @@ export function DesktopUpdater() {
       };
     }
 
+    if (installError) {
+      return {
+        id: 'desktop-update-ready',
+        priority: 200,
+        icon: ArrowUp,
+        title: 'Update Failed',
+        description: installError,
+        primaryAction: {
+          label: 'Retry',
+          variant: 'Primary',
+          onClick: handleInstall,
+        },
+        secondaryAction: {
+          label: 'Later',
+          variant: 'Secondary',
+          onClick: handleDismiss,
+        },
+      };
+    }
+
     return {
       id: 'desktop-update-ready',
       priority: 200,
@@ -251,6 +275,7 @@ export function DesktopUpdater() {
     isDownloading,
     isInstalled,
     isInstalling,
+    installError,
     handleInstall,
     handleRestart,
     handleDismiss,