diff --git a/apps/frontend/src/renderer/components/KanbanBoard.tsx b/apps/frontend/src/renderer/components/KanbanBoard.tsx
index 784aeb34..25e37d56 100644
--- a/apps/frontend/src/renderer/components/KanbanBoard.tsx
+++ b/apps/frontend/src/renderer/components/KanbanBoard.tsx
@@ -29,7 +29,7 @@ import { SortableTaskCard } from './SortableTaskCard';
 import { QueueSettingsModal } from './QueueSettingsModal';
 import { TASK_STATUS_COLUMNS, TASK_STATUS_LABELS } from '../../shared/constants';
 import { cn } from '../lib/utils';
-import { persistTaskStatus, forceCompleteTask, archiveTasks, deleteTasks, useTaskStore } from '../stores/task-store';
+import { persistTaskStatus, forceCompleteTask, archiveTasks, deleteTasks, useTaskStore, isQueueAtCapacity, DEFAULT_MAX_PARALLEL_TASKS } from '../stores/task-store';
 import { updateProjectSettings, useProjectStore } from '../stores/project-store';
 import { useKanbanSettingsStore, DEFAULT_COLUMN_WIDTH, MIN_COLUMN_WIDTH, MAX_COLUMN_WIDTH, COLLAPSED_COLUMN_WIDTH_REM, MIN_COLUMN_WIDTH_REM, MAX_COLUMN_WIDTH_REM, BASE_FONT_SIZE, pxToRem } from '../stores/kanban-settings-store';
 import { useToast } from '../hooks/use-toast';
@@ -663,7 +663,7 @@ export function KanbanBoard({ tasks, onTaskClick, onNewTaskClick, onRefresh, isR
   // Get projectId from first task
   const projectId = tasks[0]?.projectId;
   const project = projectId ? projects.find((p) => p.id === projectId) : undefined;
-  const maxParallelTasks = project?.settings?.maxParallelTasks ?? 3;
+  const maxParallelTasks = project?.settings?.maxParallelTasks ?? DEFAULT_MAX_PARALLEL_TASKS;
 
   // Queue settings modal state
   const [showQueueSettings, setShowQueueSettings] = useState(false);
@@ -947,8 +947,23 @@ export function KanbanBoard({ tasks, onTaskClick, onNewTaskClick, onRefresh, isR
    * Handle status change with worktree cleanup dialog support
    * Consolidated handler that accepts an optional task object for the dialog title
    */
-  const handleStatusChange = async (taskId: string, newStatus: TaskStatus, providedTask?: Task) => {
+  const handleStatusChange = async (taskId: string, requestedStatus: TaskStatus, providedTask?: Task) => {
     const task = providedTask || tasks.find(t => t.id === taskId);
+    let newStatus = requestedStatus;
+
+    // ============================================
+    // QUEUE SYSTEM: Enforce parallel task limit
+    // Called from both the dropdown menu and the drag-and-drop handler.
+    // Excludes the task itself from the count to handle re-entry (e.g., redundant
+    // status change or race with auto-promotion). processQueue auto-promotion
+    // calls persistTaskStatus directly, never this function.
+    // ============================================
+    if (newStatus === 'in_progress' && isQueueAtCapacity(taskId)) {
+      console.log('[Queue] In Progress full, redirecting task to Queue');
+      newStatus = 'queue';
+    }
+
+    const oldStatus = task?.status;
     const result = await persistTaskStatus(taskId, newStatus);
 
     if (!result.success) {
@@ -971,6 +986,9 @@ export function KanbanBoard({ tasks, onTaskClick, onNewTaskClick, onRefresh, isR
         });
       }
     }
+    // Note: queue auto-promotion when a task leaves in_progress is handled by the
+    // useEffect task status change listener (registerTaskStatusChangeListener), so
+    // no explicit processQueue() call is needed here.
   };
 
   /**
@@ -1402,40 +1420,10 @@ export function KanbanBoard({ tasks, onTaskClick, onNewTaskClick, onRefresh, isR
 
     if (!newStatus || newStatus === oldStatus) return;
 
-    // ============================================
-    // QUEUE SYSTEM: Enforce parallel task limit
-    // ============================================
-    if (newStatus === 'in_progress') {
-      // Get CURRENT state from store directly to avoid stale prop/memo issues during rapid dragging
-      const currentTasks = useTaskStore.getState().tasks;
-      const inProgressCount = currentTasks.filter((t) =>
-        t.status === 'in_progress' && !t.metadata?.archivedAt
-      ).length;
-
-      // If limit reached, move to queue instead
-      if (inProgressCount >= maxParallelTasks) {
-        // Only bypass the capacity check if coming from queue AND queue is NOT being processed
-        // This prevents race condition where both auto-promotion and manual drag exceed the limit
-        const isAutoPromotionInProgress = oldStatus === 'queue' && isProcessingQueueRef.current;
-
-        if (!isAutoPromotionInProgress) {
-          console.log(`[Queue] In Progress full (${inProgressCount}/${maxParallelTasks}), moving task to Queue`);
-          newStatus = 'queue';
-        }
-      }
-    }
-
-    // Persist status change to file and update local state
-    // Use handleStatusChange to properly handle worktree cleanup dialog
+    // Persist status change via handleStatusChange which enforces queue capacity,
+    // handles worktree cleanup dialogs, and calls processQueue() when a task
+    // leaves in_progress.
     await handleStatusChange(activeTaskId, newStatus, task);
-
-    // ============================================
-    // QUEUE SYSTEM: Auto-process queue when slot opens
-    // ============================================
-    if (oldStatus === 'in_progress' && newStatus !== 'in_progress') {
-      // A task left In Progress - check if we can promote from queue
-      await processQueue();
-    }
   };
 
   return (
diff --git a/apps/frontend/src/renderer/components/TaskCard.tsx b/apps/frontend/src/renderer/components/TaskCard.tsx
index d4ff08c2..652346a7 100644
--- a/apps/frontend/src/renderer/components/TaskCard.tsx
+++ b/apps/frontend/src/renderer/components/TaskCard.tsx
@@ -31,7 +31,8 @@ import {
   JSON_ERROR_PREFIX,
   JSON_ERROR_TITLE_SUFFIX
 } from '../../shared/constants';
-import { startTask, stopTask, checkTaskRunning, recoverStuckTask, isIncompleteHumanReview, archiveTasks, hasRecentActivity } from '../stores/task-store';
+import { stopTask, checkTaskRunning, recoverStuckTask, isIncompleteHumanReview, archiveTasks, hasRecentActivity, startTaskOrQueue } from '../stores/task-store';
+import { useToast } from '../hooks/use-toast';
 import type { Task, TaskCategory, ReviewReason, TaskStatus } from '../../shared/types';
 
 // Category icon mapping
@@ -133,6 +134,7 @@ export const TaskCard = memo(function TaskCard({
   onToggleSelect
 }: TaskCardProps) {
   const { t } = useTranslation(['tasks', 'errors']);
+  const { toast } = useToast();
   const [isStuck, setIsStuck] = useState(false);
   const [isRecovering, setIsRecovering] = useState(false);
   const stuckIntervalRef = useRef<NodeJS.Timeout | null>(null);
@@ -224,12 +226,21 @@ export const TaskCard = memo(function TaskCard({
     };
   }, [task.id, isRunning]);
 
-  const handleStartStop = (e: React.MouseEvent) => {
+  const handleStartStop = async (e: React.MouseEvent) => {
     e.stopPropagation();
     if (isRunning && !isStuck) {
       stopTask(task.id);
     } else {
-      startTask(task.id);
+      const result = await startTaskOrQueue(task.id);
+      if (!result.success) {
+        toast({
+          title: t('tasks:wizard.errors.startFailed'),
+          description: result.error,
+          variant: 'destructive',
+        });
+      } else if (result.action === 'queued') {
+        toast({ title: t('tasks:queue.movedToQueue') });
+      }
     }
   };
 
diff --git a/apps/frontend/src/renderer/components/task-detail/TaskDetailModal.tsx b/apps/frontend/src/renderer/components/task-detail/TaskDetailModal.tsx
index b88591c7..eebf65f2 100644
--- a/apps/frontend/src/renderer/components/task-detail/TaskDetailModal.tsx
+++ b/apps/frontend/src/renderer/components/task-detail/TaskDetailModal.tsx
@@ -32,7 +32,7 @@ import {
 } from 'lucide-react';
 import { cn } from '../../lib/utils';
 import { calculateProgress } from '../../lib/utils';
-import { startTask, stopTask, submitReview, recoverStuckTask, deleteTask, useTaskStore } from '../../stores/task-store';
+import { stopTask, submitReview, recoverStuckTask, deleteTask, useTaskStore, startTaskOrQueue } from '../../stores/task-store';
 import { useProjectStore } from '../../stores/project-store';
 import { TASK_STATUS_LABELS } from '../../../shared/constants';
 import { TaskEditDialog } from '../TaskEditDialog';
@@ -105,7 +105,16 @@ function TaskDetailModalContent({ open, task, onOpenChange, onSwitchToTerminals,
           return;
         }
       }
-      startTask(task.id);
+      const result = await startTaskOrQueue(task.id);
+      if (!result.success) {
+        toast({
+          title: t('tasks:wizard.errors.startFailed'),
+          description: result.error,
+          variant: 'destructive',
+        });
+      } else if (result.action === 'queued') {
+        toast({ title: t('tasks:queue.movedToQueue') });
+      }
     }
   };
 
diff --git a/apps/frontend/src/renderer/components/task-detail/task-review/WorkspaceMessages.tsx b/apps/frontend/src/renderer/components/task-detail/task-review/WorkspaceMessages.tsx
index f77fbb59..e9def911 100644
--- a/apps/frontend/src/renderer/components/task-detail/task-review/WorkspaceMessages.tsx
+++ b/apps/frontend/src/renderer/components/task-detail/task-review/WorkspaceMessages.tsx
@@ -1,7 +1,8 @@
 import { AlertCircle, GitMerge, Loader2, Check, RotateCcw, Play } from 'lucide-react';
 import { useState } from 'react';
+import { useTranslation } from 'react-i18next';
 import { Button } from '../../ui/button';
-import { persistTaskStatus, startTask } from '../../../stores/task-store';
+import { persistTaskStatus, startTaskOrQueue } from '../../../stores/task-store';
 import type { Task } from '../../../../shared/types';
 
 interface LoadingMessageProps {
@@ -31,8 +32,11 @@ interface NoWorkspaceMessageProps {
  * Displays message when no workspace is found for the task
  */
 export function NoWorkspaceMessage({ task, onClose }: NoWorkspaceMessageProps) {
+  const { t } = useTranslation(['tasks']);
   const [isMarkingDone, setIsMarkingDone] = useState(false);
   const [isProceeding, setIsProceeding] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+  const [notice, setNotice] = useState<string | null>(null);
 
   const isPlanReview =
     task?.status === 'human_review' &&
@@ -57,10 +61,18 @@ export function NoWorkspaceMessage({ task, onClose }: NoWorkspaceMessageProps) {
     if (!task) return;
 
     setIsProceeding(true);
+    setError(null);
+    setNotice(null);
     try {
-      await startTask(task.id);
+      const result = await startTaskOrQueue(task.id);
+      if (!result.success) {
+        setError(result.error || t('tasks:wizard.errors.startFailed'));
+      } else if (result.action === 'queued') {
+        setNotice(t('tasks:queue.movedToQueue'));
+      }
     } catch (err) {
       console.error('Error proceeding to coding:', err);
+      setError(err instanceof Error ? err.message : 'Failed to start task');
     } finally {
       setIsProceeding(false);
     }
@@ -120,6 +132,13 @@ export function NoWorkspaceMessage({ task, onClose }: NoWorkspaceMessageProps) {
           )}
         </Button>
       )}
+
+      {error && (
+        <p className="text-xs text-destructive mt-2">{error}</p>
+      )}
+      {notice && (
+        <p className="text-xs text-muted-foreground mt-2">{notice}</p>
+      )}
     </div>
   );
 }
diff --git a/apps/frontend/src/renderer/stores/task-store.ts b/apps/frontend/src/renderer/stores/task-store.ts
index 98e21f7c..6b28e88c 100644
--- a/apps/frontend/src/renderer/stores/task-store.ts
+++ b/apps/frontend/src/renderer/stores/task-store.ts
@@ -2,6 +2,10 @@ import { create } from 'zustand';
 import { arrayMove } from '@dnd-kit/sortable';
 import type { Task, TaskStatus, SubtaskStatus, ImplementationPlan, Subtask, TaskMetadata, ExecutionProgress, ExecutionPhase, ReviewReason, TaskDraft, ImageAttachment, TaskOrderState } from '../../shared/types';
 import { debugLog, debugWarn } from '../../shared/utils/debug-logger';
+import { useProjectStore } from './project-store';
+
+/** Default max parallel tasks when no project setting is configured */
+export const DEFAULT_MAX_PARALLEL_TASKS = 3;
 
 interface TaskState {
   tasks: Task[];
@@ -826,6 +830,54 @@ export async function forceCompleteTask(taskId: string): Promise<PersistStatusRe
   return persistTaskStatus(taskId, 'done', { forceCleanup: true });
 }
 
+/**
+ * Check if the in_progress queue is at capacity.
+ * @param excludeTaskId - Task ID to exclude from the count (e.g., when restarting a stuck task already in in_progress)
+ */
+export function isQueueAtCapacity(excludeTaskId?: string): boolean {
+  const maxParallelTasks = useProjectStore.getState().getActiveProject()?.settings?.maxParallelTasks ?? DEFAULT_MAX_PARALLEL_TASKS;
+  const currentTasks = useTaskStore.getState().tasks;
+  const inProgressCount = currentTasks.filter((t) =>
+    t.status === 'in_progress' && !t.metadata?.archivedAt && (!excludeTaskId || t.id !== excludeTaskId)
+  ).length;
+  return inProgressCount >= maxParallelTasks;
+}
+
+export interface StartTaskOrQueueResult {
+  /** Whether the task was started ('started') or redirected to queue ('queued') */
+  action: 'started' | 'queued';
+  success: boolean;
+  error?: string;
+}
+
+/**
+ * Start a task or queue it if parallel task capacity is full.
+ * If the task is already in_progress (stuck restart), it is excluded from the
+ * capacity count so restarting is always allowed.
+ * Returns a result so callers can provide user-facing feedback.
+ *
+ * For action 'started', success indicates the IPC start command was dispatched.
+ * Backend failures are surfaced asynchronously through task status change events,
+ * not through this return value.
+ */
+export async function startTaskOrQueue(taskId: string): Promise<StartTaskOrQueueResult> {
+  const task = useTaskStore.getState().tasks.find(t => t.id === taskId);
+  // Exclude this task from the capacity check when it's already in_progress (stuck restart)
+  const excludeId = task?.status === 'in_progress' ? taskId : undefined;
+
+  if (isQueueAtCapacity(excludeId)) {
+    const result = await persistTaskStatus(taskId, 'queue');
+    if (!result.success) {
+      console.error('[Queue] Failed to queue task:', taskId, result.error);
+      return { action: 'queued', success: false, error: result.error };
+    }
+    return { action: 'queued', success: true };
+  }
+
+  startTask(taskId);
+  return { action: 'started', success: true };
+}
+
 /**
  * Update task title/description/metadata and persist to file
  */
diff --git a/apps/frontend/src/shared/i18n/locales/en/tasks.json b/apps/frontend/src/shared/i18n/locales/en/tasks.json
index 22e3ddb8..ecd78827 100644
--- a/apps/frontend/src/shared/i18n/locales/en/tasks.json
+++ b/apps/frontend/src/shared/i18n/locales/en/tasks.json
@@ -222,7 +222,8 @@
       "useWorktreeDescription": "Creates changes in a separate git worktree for safe review before merging. Disable to build directly in your project (faster but riskier)."
     },
     "errors": {
-      "createFailed": "Failed to create task. Please try again."
+      "createFailed": "Failed to create task. Please try again.",
+      "startFailed": "Failed to start task"
     }
   },
   "feedback": {
diff --git a/apps/frontend/src/shared/i18n/locales/fr/tasks.json b/apps/frontend/src/shared/i18n/locales/fr/tasks.json
index 2442b2b3..00af23a4 100644
--- a/apps/frontend/src/shared/i18n/locales/fr/tasks.json
+++ b/apps/frontend/src/shared/i18n/locales/fr/tasks.json
@@ -2,6 +2,7 @@
   "refreshTasks": "Actualiser les tâches",
   "status": {
     "backlog": "Backlog",
+    "queue": "File d'attente",
     "todo": "À faire",
     "in_progress": "En cours",
     "review": "Révision",
@@ -221,7 +222,8 @@
       "useWorktreeDescription": "Crée les changements dans un worktree git séparé pour une révision sécurisée avant la fusion. Désactivez pour travailler directement dans votre projet (plus rapide mais risqué)."
     },
     "errors": {
-      "createFailed": "Échec de la création de la tâche. Veuillez réessayer."
+      "createFailed": "Échec de la création de la tâche. Veuillez réessayer.",
+      "startFailed": "Échec du démarrage de la tâche"
     }
   },
   "feedback": {