feat(KB-051): add duplicate task button in task detail modal

- Add duplicateTask action to useTasks hook for creating task copies

- Add Duplicate button to TaskDetailModal with visual styling

- Wire up duplicateTask action through App.tsx task handlers

- Add comprehensive tests for duplicate button functionality

- Include changeset for the new duplicate task feature

packages/dashboard/app/App.tsx

@@ -36,7 +36,7 @@ function AppInner() {
     return "board";
   });
   const [githubTokenConfigured, setGithubTokenConfigured] = useState(false);
-  const { tasks, createTask, moveTask, deleteTask, mergeTask, retryTask, updateTask } = useTasks();
+  const { tasks, createTask, moveTask, deleteTask, mergeTask, retryTask, updateTask, duplicateTask } = useTasks();
 
   useEffect(() => {
     fetchConfig()
@@ -185,6 +185,7 @@ function AppInner() {
           onDeleteTask={deleteTask}
           onMergeTask={mergeTask}
           onRetryTask={retryTask}
+          onDuplicateTask={duplicateTask}
           addToast={addToast}
           githubTokenConfigured={githubTokenConfigured}
         />

packages/dashboard/app/components/TaskDetailModal.tsx

@@ -56,6 +56,7 @@ interface TaskDetailModalProps {
   onDeleteTask: (id: string) => Promise<Task>;
   onMergeTask: (id: string) => Promise<MergeResult>;
   onRetryTask?: (id: string) => Promise<Task>;
+  onDuplicateTask?: (id: string) => Promise<Task>;
   addToast: (message: string, type?: ToastType) => void;
   githubTokenConfigured?: boolean;
 }
@@ -73,6 +74,7 @@ export function TaskDetailModal({
   onDeleteTask,
   onMergeTask,
   onRetryTask,
+  onDuplicateTask,
   addToast,
   githubTokenConfigured,
 }: TaskDetailModalProps) {
@@ -158,6 +160,18 @@ export function TaskDetailModal({
     }
   }, [task.id, onRetryTask, onClose, addToast]);
 
+  const handleDuplicate = useCallback(async () => {
+    if (!onDuplicateTask) return;
+    if (!confirm(`Duplicate ${task.id}? This will create a new task in Triage with the same description and prompt.`)) return;
+    try {
+      const newTask = await onDuplicateTask(task.id);
+      onClose();
+      addToast(`Duplicated ${task.id} → ${newTask.id}`, "success");
+    } catch (err: any) {
+      addToast(err.message, "error");
+    }
+  }, [task.id, onDuplicateTask, onClose, addToast]);
+
   const handleTogglePause = useCallback(async () => {
     try {
       if (task.paused) {
@@ -661,6 +675,11 @@ export function TaskDetailModal({
           <button className="btn btn-danger btn-sm" onClick={handleDelete}>
             Delete
           </button>
+          {onDuplicateTask && (
+            <button className="btn btn-sm" onClick={handleDuplicate}>
+              Duplicate
+            </button>
+          )}
           {task.status === "failed" && onRetryTask && (
             <button className="btn btn-warning btn-sm" onClick={handleRetry}>
               Retry

packages/dashboard/app/components/__tests__/TaskDetailModal.test.tsx

@@ -12,6 +12,7 @@ vi.mock("../../api", () => ({
   requestSpecRevision: vi.fn().mockResolvedValue({}),
   approvePlan: vi.fn().mockResolvedValue({}),
   rejectPlan: vi.fn().mockResolvedValue({}),
+  duplicateTask: vi.fn().mockResolvedValue({}),
 }));
 
 vi.mock("../../hooks/useAgentLogs", () => ({
@@ -1807,4 +1808,179 @@ describe("TaskDetailModal", () => {
       window.confirm = originalConfirm;
     });
   });
+
+  describe("Duplicate button", () => {
+    it("renders Duplicate button in modal actions when onDuplicateTask is provided", () => {
+      render(
+        <TaskDetailModal
+          task={makeTask()}
+          onClose={noop}
+          onMoveTask={noopMove}
+          onDeleteTask={noopDelete}
+          onMergeTask={noopMerge}
+          onOpenDetail={noopOpenDetail}
+          onDuplicateTask={vi.fn()}
+          addToast={noop}
+        />,
+      );
+
+      expect(screen.getByText("Duplicate")).toBeTruthy();
+    });
+
+    it("does NOT render Duplicate button when onDuplicateTask is not provided", () => {
+      render(
+        <TaskDetailModal
+          task={makeTask()}
+          onClose={noop}
+          onMoveTask={noopMove}
+          onDeleteTask={noopDelete}
+          onMergeTask={noopMerge}
+          onOpenDetail={noopOpenDetail}
+          addToast={noop}
+        />,
+      );
+
+      expect(screen.queryByText("Duplicate")).toBeNull();
+    });
+
+    it("clicking Duplicate shows confirmation dialog", () => {
+      const originalConfirm = window.confirm;
+      window.confirm = vi.fn(() => false);
+
+      render(
+        <TaskDetailModal
+          task={makeTask({ id: "KB-001" })}
+          onClose={noop}
+          onMoveTask={noopMove}
+          onDeleteTask={noopDelete}
+          onMergeTask={noopMerge}
+          onOpenDetail={noopOpenDetail}
+          onDuplicateTask={vi.fn()}
+          addToast={noop}
+        />,
+      );
+
+      fireEvent.click(screen.getByText("Duplicate"));
+
+      expect(window.confirm).toHaveBeenCalledWith(
+        "Duplicate KB-001? This will create a new task in Triage with the same description and prompt."
+      );
+
+      window.confirm = originalConfirm;
+    });
+
+    it("confirming duplicate calls onDuplicateTask and closes modal", async () => {
+      const originalConfirm = window.confirm;
+      window.confirm = vi.fn(() => true);
+
+      const mockDuplicate = vi.fn().mockResolvedValue({ id: "KB-002" } as Task);
+      const onClose = vi.fn();
+
+      render(
+        <TaskDetailModal
+          task={makeTask({ id: "KB-001" })}
+          onClose={onClose}
+          onMoveTask={noopMove}
+          onDeleteTask={noopDelete}
+          onMergeTask={noopMerge}
+          onOpenDetail={noopOpenDetail}
+          onDuplicateTask={mockDuplicate}
+          addToast={noop}
+        />,
+      );
+
+      fireEvent.click(screen.getByText("Duplicate"));
+
+      await waitFor(() => {
+        expect(mockDuplicate).toHaveBeenCalledWith("KB-001");
+        expect(onClose).toHaveBeenCalled();
+      });
+
+      window.confirm = originalConfirm;
+    });
+
+    it("successful duplicate shows success toast with new task ID", async () => {
+      const originalConfirm = window.confirm;
+      window.confirm = vi.fn(() => true);
+
+      const mockDuplicate = vi.fn().mockResolvedValue({ id: "KB-002" } as Task);
+      const addToast = vi.fn();
+
+      render(
+        <TaskDetailModal
+          task={makeTask({ id: "KB-001" })}
+          onClose={noop}
+          onMoveTask={noopMove}
+          onDeleteTask={noopDelete}
+          onMergeTask={noopMerge}
+          onOpenDetail={noopOpenDetail}
+          onDuplicateTask={mockDuplicate}
+          addToast={addToast}
+        />,
+      );
+
+      fireEvent.click(screen.getByText("Duplicate"));
+
+      await waitFor(() => {
+        expect(addToast).toHaveBeenCalledWith("Duplicated KB-001 → KB-002", "success");
+      });
+
+      window.confirm = originalConfirm;
+    });
+
+    it("cancelling confirmation does not call onDuplicateTask", () => {
+      const originalConfirm = window.confirm;
+      window.confirm = vi.fn(() => false);
+
+      const mockDuplicate = vi.fn().mockResolvedValue({ id: "KB-002" } as Task);
+
+      render(
+        <TaskDetailModal
+          task={makeTask({ id: "KB-001" })}
+          onClose={noop}
+          onMoveTask={noopMove}
+          onDeleteTask={noopDelete}
+          onMergeTask={noopMerge}
+          onOpenDetail={noopOpenDetail}
+          onDuplicateTask={mockDuplicate}
+          addToast={noop}
+        />,
+      );
+
+      fireEvent.click(screen.getByText("Duplicate"));
+
+      expect(mockDuplicate).not.toHaveBeenCalled();
+
+      window.confirm = originalConfirm;
+    });
+
+    it("shows error toast when duplicate fails", async () => {
+      const originalConfirm = window.confirm;
+      window.confirm = vi.fn(() => true);
+
+      const mockDuplicate = vi.fn().mockRejectedValue(new Error("Duplicate failed"));
+      const addToast = vi.fn();
+
+      render(
+        <TaskDetailModal
+          task={makeTask({ id: "KB-001" })}
+          onClose={noop}
+          onMoveTask={noopMove}
+          onDeleteTask={noopDelete}
+          onMergeTask={noopMerge}
+          onOpenDetail={noopOpenDetail}
+          onDuplicateTask={mockDuplicate}
+          addToast={addToast}
+        />,
+      );
+
+      fireEvent.click(screen.getByText("Duplicate"));
+
+      await waitFor(() => {
+        expect(addToast).toHaveBeenCalledWith("Duplicate failed", "error");
+      });
+
+      window.confirm = originalConfirm;
+    });
+  });
 });

packages/dashboard/app/hooks/useTasks.ts

@@ -118,6 +118,10 @@ export function useTasks() {
     return api.retryTask(id);
   }, []);
 
+  const duplicateTask = useCallback(async (id: string): Promise<Task> => {
+    return api.duplicateTask(id);
+  }, []);
+
   const updateTask = useCallback(async (
     id: string,
     updates: { title?: string; description?: string; dependencies?: string[] }
@@ -152,5 +156,5 @@ export function useTasks() {
     }
   }, []);
 
-  return { tasks, createTask, moveTask, deleteTask, mergeTask, retryTask, updateTask };
+  return { tasks, createTask, moveTask, deleteTask, mergeTask, retryTask, duplicateTask, updateTask };
 }