fix(tasks): prevent concurrent execution and improve button UX

Phase 1 fix for concurrent execution issue:
- Backend: Check for in_progress tasks before scheduling new execution
- Frontend: Disable button when tasks are already running
- Frontend: Show "Running..." state and updated message when execution active
- Add 2 new tests for execution blocking behavior

Author: Test User

codeframe/ui/routers/tasks.py

@@ -450,6 +450,19 @@ async def assign_pending_tasks(
             message="No pending unassigned tasks to assign."
         )
 
+    # Check if execution is already in progress (Phase 1 fix for concurrent execution)
+    in_progress_tasks = [t for t in tasks if t.status == TaskStatus.IN_PROGRESS]
+    if in_progress_tasks:
+        logger.info(
+            f"⏳ Execution already in progress for project {project_id}: "
+            f"{len(in_progress_tasks)} tasks running"
+        )
+        return TaskAssignmentResponse(
+            success=True,
+            pending_count=pending_count,
+            message=f"Execution already in progress ({len(in_progress_tasks)} task(s) running). Please wait."
+        )
+
     # Schedule multi-agent execution in background
     api_key = os.environ.get("ANTHROPIC_API_KEY")
     if api_key:

tests/ui/test_assign_pending_tasks.py

@@ -239,7 +239,69 @@ async def test_assign_pending_tasks_only_counts_unassigned(
                 current_user=mock_user
             )
 
-        assert response.pending_count == 1  # Only the first task
+        # Should not trigger because there's an in_progress task
+        assert response.pending_count == 1
+        assert "in progress" in response.message.lower()
+        mock_background_tasks.add_task.assert_not_called()
+
+    @pytest.mark.asyncio
+    async def test_assign_pending_tasks_blocked_when_execution_in_progress(
+        self, mock_db, mock_user, mock_manager, mock_background_tasks
+    ):
+        """Test that assignment is blocked when tasks are already in progress."""
+        from codeframe.ui.routers.tasks import assign_pending_tasks
+
+        # Setup: 2 pending tasks + 1 in progress
+        mock_db.get_project_tasks.return_value = [
+            Task(id=1, project_id=1, title="Task 1", status=TaskStatus.PENDING, assigned_to=None),
+            Task(id=2, project_id=1, title="Task 2", status=TaskStatus.PENDING, assigned_to=None),
+            Task(id=3, project_id=1, title="Task 3", status=TaskStatus.IN_PROGRESS, assigned_to="agent-1"),
+        ]
+
+        with patch("codeframe.ui.routers.tasks.manager", mock_manager), \
+             patch.dict(os.environ, {"ANTHROPIC_API_KEY": "test-key"}):
+            response = await assign_pending_tasks(
+                project_id=1,
+                background_tasks=mock_background_tasks,
+                db=mock_db,
+                current_user=mock_user
+            )
+
+        # Should return success but NOT schedule execution
+        assert response.success is True
+        assert response.pending_count == 2
+        assert "in progress" in response.message.lower()
+        assert "1 task" in response.message.lower()  # Reports 1 task running
+        mock_background_tasks.add_task.assert_not_called()
+
+    @pytest.mark.asyncio
+    async def test_assign_pending_tasks_allowed_when_no_execution_in_progress(
+        self, mock_db, mock_user, mock_manager, mock_background_tasks
+    ):
+        """Test that assignment proceeds when no tasks are in progress."""
+        from codeframe.ui.routers.tasks import assign_pending_tasks
+
+        # Setup: Only pending and completed tasks, no in_progress
+        mock_db.get_project_tasks.return_value = [
+            Task(id=1, project_id=1, title="Task 1", status=TaskStatus.PENDING, assigned_to=None),
+            Task(id=2, project_id=1, title="Task 2", status=TaskStatus.PENDING, assigned_to=None),
+            Task(id=3, project_id=1, title="Task 3", status=TaskStatus.COMPLETED, assigned_to="agent-1"),
+        ]
+
+        with patch("codeframe.ui.routers.tasks.manager", mock_manager), \
+             patch.dict(os.environ, {"ANTHROPIC_API_KEY": "test-key"}):
+            response = await assign_pending_tasks(
+                project_id=1,
+                background_tasks=mock_background_tasks,
+                db=mock_db,
+                current_user=mock_user
+            )
+
+        # Should schedule execution
+        assert response.success is True
+        assert response.pending_count == 2
+        assert "started" in response.message.lower()
+        mock_background_tasks.add_task.assert_called_once()
 
 
 class TestAssignPendingTasksResponseModel:

web-ui/src/components/TaskList.tsx

@@ -232,6 +232,11 @@ const TaskList = memo(function TaskList({ projectId }: TaskListProps) {
     ).length;
   }, [projectTasks]);
 
+  // Check if execution is already in progress (Phase 1 fix for concurrent execution)
+  const hasTasksInProgress = useMemo(() => {
+    return projectTasks.some((task) => task.status === 'in_progress');
+  }, [projectTasks]);
+
   // Handler for Assign Tasks button (Issue #248 fix)
   const handleAssignTasks = useCallback(async () => {
     setIsAssigning(true);
@@ -308,16 +313,20 @@ const TaskList = memo(function TaskList({ projectId }: TaskListProps) {
             <div className="flex-1">
               <h3 className="font-medium text-foreground">Tasks Pending Assignment</h3>
               <p className="text-sm text-muted-foreground">
-                {pendingUnassignedCount} task{pendingUnassignedCount !== 1 ? 's are' : ' is'} waiting to be assigned to agents
+                {hasTasksInProgress ? (
+                  <>Execution in progress. {pendingUnassignedCount} task{pendingUnassignedCount !== 1 ? 's' : ''} waiting...</>
+                ) : (
+                  <>{pendingUnassignedCount} task{pendingUnassignedCount !== 1 ? 's are' : ' is'} waiting to be assigned to agents</>
+                )}
               </p>
             </div>
             <button
               data-testid="assign-tasks-button"
               onClick={handleAssignTasks}
-              disabled={isAssigning}
+              disabled={isAssigning || hasTasksInProgress}
               className="px-4 py-2 bg-primary text-primary-foreground rounded-md hover:bg-primary/90 disabled:opacity-50 disabled:cursor-not-allowed transition-colors"
             >
-              {isAssigning ? 'Assigning...' : 'Assign Tasks'}
+              {isAssigning ? 'Assigning...' : hasTasksInProgress ? 'Running...' : 'Assign Tasks'}
             </button>
           </div>
           {assignmentError && (