auto-claude: subtask-9-4 - Add comprehensive error handling for all IPC window operations

- Add window error translations to en/fr errors.json
- Add toast notifications for pop-out project errors in ProjectTabBar
- Add toast notifications for pop-out view errors in Sidebar
- Ensure loading states reset properly in finally blocks
- User-facing error messages for window creation failures

apps/frontend/src/renderer/components/ProjectTabBar.tsx

@@ -7,6 +7,7 @@ import { SortableProjectTab } from './SortableProjectTab';
 import { UsageIndicator } from './UsageIndicator';
 import { AuthStatusIndicator } from './AuthStatusIndicator';
 import { useWindowStore } from '../stores/window-store';
+import { useToast } from '../hooks/use-toast';
 import type { Project } from '../../shared/types';
 
 interface ProjectTabBarProps {
@@ -29,7 +30,8 @@ export function ProjectTabBar({
   className,
   onSettingsClick
 }: ProjectTabBarProps) {
-  const { t } = useTranslation('common');
+  const { t } = useTranslation(['common', 'errors']);
+  const { toast } = useToast();
   const { isProjectPoppedOut, setWindowLoading, addPoppedOutProject, isWindowLoading } = useWindowStore();
 
   // Handler for popping out a project into a new window
@@ -52,7 +54,11 @@ export function ProjectTabBar({
           console.log(`Project ${projectId} already popped out, focused existing window ${error.existingWindowId}`);
         } else {
           console.error('Failed to pop out project:', error.message);
-          // TODO: Show error notification to user
+          toast({
+            title: t('errors:window.popOutProjectFailed'),
+            description: t('errors:window.windowCreationFailed', { message: error.message }),
+            variant: 'destructive'
+          });
         }
         return;
       }
@@ -63,7 +69,11 @@ export function ProjectTabBar({
       console.log(`Project ${projectId} popped out to window ${successResult.windowId}`);
     } catch (error) {
       console.error('Failed to pop out project:', error);
-      // TODO: Show error notification to user
+      toast({
+        title: t('errors:window.popOutProjectFailed'),
+        description: error instanceof Error ? error.message : t('errors:window.genericError'),
+        variant: 'destructive'
+      });
     } finally {
       setWindowLoading(projectId, false);
     }

apps/frontend/src/renderer/components/Sidebar.tsx

@@ -61,6 +61,7 @@ import { GitSetupModal } from './GitSetupModal';
 import { RateLimitIndicator } from './RateLimitIndicator';
 import { ClaudeCodeStatusBadge } from './ClaudeCodeStatusBadge';
 import { UpdateBanner } from './UpdateBanner';
+import { useToast } from '../hooks/use-toast';
 import type { Project, GitStatus } from '../../shared/types';
 
 export type SidebarView = 'kanban' | 'terminals' | 'roadmap' | 'context' | 'ideation' | 'github-issues' | 'gitlab-issues' | 'github-prs' | 'gitlab-merge-requests' | 'changelog' | 'insights' | 'worktrees' | 'agent-tools';
@@ -110,7 +111,8 @@ export function Sidebar({
   activeView = 'kanban',
   onViewChange
 }: SidebarProps) {
-  const { t } = useTranslation(['navigation', 'dialogs', 'common']);
+  const { t } = useTranslation(['navigation', 'dialogs', 'common', 'errors']);
+  const { toast } = useToast();
   const projects = useProjectStore((state) => state.projects);
   const selectedProjectId = useProjectStore((state) => state.selectedProjectId);
   const settings = useSettingsStore((state) => state.settings);
@@ -321,6 +323,11 @@ export function Sidebar({
           await window.electronAPI.window.focusWindow(error.existingWindowId);
         } else {
           console.error('Failed to pop out view:', error.message);
+          toast({
+            title: t('errors:window.popOutViewFailed'),
+            description: t('errors:window.windowCreationFailed', { message: error.message }),
+            variant: 'destructive'
+          });
         }
         return;
       }
@@ -330,6 +337,11 @@ export function Sidebar({
       addPoppedOutView(selectedProjectId, view, successResult.windowId);
     } catch (error) {
       console.error('Failed to pop out view:', error);
+      toast({
+        title: t('errors:window.popOutViewFailed'),
+        description: error instanceof Error ? error.message : t('errors:window.genericError'),
+        variant: 'destructive'
+      });
     } finally {
       setWindowLoading(viewKey, false);
     }

apps/frontend/src/shared/i18n/locales/en/errors.json

@@ -5,5 +5,12 @@
       "titleSuffix": "(JSON Error)",
       "description": "⚠️ JSON Parse Error: {{error}}\n\nThe implementation_plan.json file is malformed. Run the backend auto-fix or manually repair the file."
     }
+  },
+  "window": {
+    "popOutProjectFailed": "Failed to pop out project",
+    "popOutViewFailed": "Failed to pop out view",
+    "windowCreationFailed": "Could not create window: {{message}}",
+    "sourceWindowNotFound": "Source window not found",
+    "genericError": "An unexpected error occurred"
   }
 }

apps/frontend/src/shared/i18n/locales/fr/errors.json

@@ -5,5 +5,12 @@
       "titleSuffix": "(Erreur JSON)",
       "description": "⚠️ Erreur d'analyse JSON : {{error}}\n\nLe fichier implementation_plan.json est malformé. Exécutez la correction automatique du backend ou réparez le fichier manuellement."
     }
+  },
+  "window": {
+    "popOutProjectFailed": "Échec de l'extraction du projet",
+    "popOutViewFailed": "Échec de l'extraction de la vue",
+    "windowCreationFailed": "Impossible de créer la fenêtre : {{message}}",
+    "sourceWindowNotFound": "Fenêtre source introuvable",
+    "genericError": "Une erreur inattendue s'est produite"
   }
 }