feat(KB-069): add Archive All Done feature

- Add archiveAllDone method to TaskStore with filtering and batch archive
- Add POST /tasks/archive-all-done API endpoint with tests
- Add useTasks hook support and API function for archiveAllDone
- Add Archive All button to done column header in Board UI
- Wire up onArchiveAllDone through Board component hierarchy

packages/core/src/store.test.ts

@@ -2113,6 +2113,96 @@ describe("TaskStore", () => {
     });
   });
 
+  describe("archiveAllDone", () => {
+    it("archives multiple done tasks", async () => {
+      const task1 = await store.createTask({ description: "Test task 1" });
+      const task2 = await store.createTask({ description: "Test task 2" });
+      const task3 = await store.createTask({ description: "Test task 3" });
+
+      // Move all to done
+      for (const task of [task1, task2, task3]) {
+        await store.moveTask(task.id, "todo");
+        await store.moveTask(task.id, "in-progress");
+        await store.moveTask(task.id, "in-review");
+        await store.moveTask(task.id, "done");
+      }
+
+      const archived = await store.archiveAllDone();
+
+      expect(archived).toHaveLength(3);
+      expect(archived.every((t) => t.column === "archived")).toBe(true);
+    });
+
+    it("returns empty array when no done tasks exist", async () => {
+      const result = await store.archiveAllDone();
+
+      expect(result).toEqual([]);
+    });
+
+    it("emits task:moved event for each archived task", async () => {
+      const task1 = await store.createTask({ description: "Test task 1" });
+      const task2 = await store.createTask({ description: "Test task 2" });
+
+      for (const task of [task1, task2]) {
+        await store.moveTask(task.id, "todo");
+        await store.moveTask(task.id, "in-progress");
+        await store.moveTask(task.id, "in-review");
+        await store.moveTask(task.id, "done");
+      }
+
+      const events: any[] = [];
+      store.on("task:moved", (data) => events.push(data));
+
+      await store.archiveAllDone();
+
+      expect(events).toHaveLength(2);
+      expect(events.every((e) => e.from === "done" && e.to === "archived")).toBe(true);
+    });
+
+    it("does not affect tasks in other columns", async () => {
+      const doneTask = await store.createTask({ description: "Done task" });
+      await store.moveTask(doneTask.id, "todo");
+      await store.moveTask(doneTask.id, "in-progress");
+      await store.moveTask(doneTask.id, "in-review");
+      await store.moveTask(doneTask.id, "done");
+
+      const todoTask = await store.createTask({ description: "Todo task" });
+      await store.moveTask(todoTask.id, "todo");
+
+      const inProgressTask = await store.createTask({ description: "In progress task" });
+      await store.moveTask(inProgressTask.id, "todo");
+      await store.moveTask(inProgressTask.id, "in-progress");
+
+      await store.archiveAllDone();
+
+      const fetchedTodo = await store.getTask(todoTask.id);
+      const fetchedInProgress = await store.getTask(inProgressTask.id);
+
+      expect(fetchedTodo.column).toBe("todo");
+      expect(fetchedInProgress.column).toBe("in-progress");
+    });
+
+    it("archives only done tasks when mixed columns exist", async () => {
+      const doneTask1 = await store.createTask({ description: "Done task 1" });
+      const doneTask2 = await store.createTask({ description: "Done task 2" });
+      const todoTask = await store.createTask({ description: "Todo task" });
+
+      for (const task of [doneTask1, doneTask2]) {
+        await store.moveTask(task.id, "todo");
+        await store.moveTask(task.id, "in-progress");
+        await store.moveTask(task.id, "in-review");
+        await store.moveTask(task.id, "done");
+      }
+
+      await store.moveTask(todoTask.id, "todo");
+
+      const archived = await store.archiveAllDone();
+
+      expect(archived).toHaveLength(2);
+      expect(archived.map((t) => t.id).sort()).toEqual([doneTask1.id, doneTask2.id].sort());
+    });
+  });
+
   describe("VALID_TRANSITIONS — invalid archived transitions via moveTask", () => {
     it("moveTask from archived → in-progress should fail", async () => {
       const task = await store.createTask({ description: "Test task" });

packages/core/src/store.ts

@@ -875,6 +875,26 @@ export class TaskStore extends EventEmitter<TaskStoreEvents> {
     });
   }
 
+  /**
+   * Archive all tasks currently in the "done" column.
+   * Returns an array of archived tasks.
+   */
+  async archiveAllDone(): Promise<Task[]> {
+    const tasks = await this.listTasks();
+    const doneTasks = tasks.filter((t) => t.column === "done");
+    
+    if (doneTasks.length === 0) {
+      return [];
+    }
+
+    // Archive all done tasks concurrently
+    const archivedTasks = await Promise.all(
+      doneTasks.map((task) => this.archiveTask(task.id))
+    );
+
+    return archivedTasks;
+  }
+
   /**
    * Archive a done task (move from done → archived).
    * Logs the action and emits `task:moved` event.

packages/dashboard/app/App.tsx

@@ -46,7 +46,7 @@ function AppInner() {
   });
   const [searchQuery, setSearchQuery] = useState("");
   const [githubTokenConfigured, setGithubTokenConfigured] = useState(false);
-  const { tasks, createTask, moveTask, deleteTask, mergeTask, retryTask, updateTask, duplicateTask, archiveTask, unarchiveTask } = useTasks();
+  const { tasks, createTask, moveTask, deleteTask, mergeTask, retryTask, updateTask, duplicateTask, archiveTask, unarchiveTask, archiveAllDone } = useTasks();
 
   // Theme management
   const { themeMode, colorTheme, setThemeMode, setColorTheme } = useTheme();
@@ -216,6 +216,7 @@ function AppInner() {
           onUpdateTask={updateTask}
           onArchiveTask={archiveTask}
           onUnarchiveTask={unarchiveTask}
+          onArchiveAllDone={archiveAllDone}
           searchQuery={searchQuery}
         />
       ) : (

packages/dashboard/app/api.ts

@@ -123,6 +123,12 @@ export function unarchiveTask(id: string): Promise<Task> {
   return api<Task>(`/tasks/${id}/unarchive`, { method: "POST" });
 }
 
+export function archiveAllDone(): Promise<Task[]> {
+  return api<{ archived: Task[] }>("/tasks/archive-all-done", { method: "POST" }).then(
+    (response) => response.archived
+  );
+}
+
 export function approvePlan(id: string): Promise<Task> {
   return api<Task>(`/tasks/${id}/approve-plan`, { method: "POST" });
 }

packages/dashboard/app/components/Board.tsx

@@ -22,6 +22,7 @@ interface BoardProps {
   ) => Promise<Task>;
   onArchiveTask?: (id: string) => Promise<Task>;
   onUnarchiveTask?: (id: string) => Promise<Task>;
+  onArchiveAllDone?: () => Promise<Task[]>;
   searchQuery?: string;
 }
 
@@ -41,7 +42,7 @@ function areTaskArraysEqual(previous: Task[], next: Task[]): boolean {
   return previous.every((task, index) => task === next[index]);
 }
 
-export function Board({ tasks, maxConcurrent, onMoveTask, onOpenDetail, addToast, onQuickCreate, onNewTask, autoMerge, onToggleAutoMerge, globalPaused, onUpdateTask, onArchiveTask, onUnarchiveTask, searchQuery = "" }: BoardProps) {
+export function Board({ tasks, maxConcurrent, onMoveTask, onOpenDetail, addToast, onQuickCreate, onNewTask, autoMerge, onToggleAutoMerge, globalPaused, onUpdateTask, onArchiveTask, onUnarchiveTask, onArchiveAllDone, searchQuery = "" }: BoardProps) {
   const [archivedCollapsed, setArchivedCollapsed] = useState(true);
   const { fetchBatch } = useBatchBadgeFetch();
   const debounceTimeoutRef = useRef<ReturnType<typeof setTimeout> | null>(null);
@@ -147,6 +148,7 @@ export function Board({ tasks, maxConcurrent, onMoveTask, onOpenDetail, addToast
           onUnarchiveTask={onUnarchiveTask}
           {...(col === "triage" ? { onQuickCreate, onNewTask } : {})}
           {...(col === "in-review" ? { autoMerge, onToggleAutoMerge } : {})}
+          {...(col === "done" ? { onArchiveAllDone } : {})}
           {...(col === "archived" ? { collapsed: archivedCollapsed, onToggleCollapse: handleToggleArchivedCollapse } : {})}
         />
       ))}

packages/dashboard/app/components/Column.tsx

@@ -7,7 +7,7 @@ import { WorktreeGroup } from "./WorktreeGroup";
 import { QuickEntryBox } from "./QuickEntryBox";
 import { groupByWorktree } from "../utils/worktreeGrouping";
 import type { ToastType } from "../hooks/useToast";
-import { ChevronDown, ChevronUp } from "lucide-react";
+import { ChevronDown, ChevronUp, Archive } from "lucide-react";
 
 const PAGINATED_COLUMN_THRESHOLD = 100;
 const VISIBLE_TASKS_INITIAL = 50;
@@ -31,11 +31,12 @@ interface ColumnProps {
   ) => Promise<Task>;
   onArchiveTask?: (id: string) => Promise<Task>;
   onUnarchiveTask?: (id: string) => Promise<Task>;
+  onArchiveAllDone?: () => Promise<Task[]>;
   collapsed?: boolean;
   onToggleCollapse?: () => void;
 }
 
-function ColumnComponent({ column, tasks, maxConcurrent, onMoveTask, onOpenDetail, addToast, onQuickCreate, onNewTask, autoMerge, onToggleAutoMerge, globalPaused, onUpdateTask, onArchiveTask, onUnarchiveTask, collapsed, onToggleCollapse }: ColumnProps) {
+function ColumnComponent({ column, tasks, maxConcurrent, onMoveTask, onOpenDetail, addToast, onQuickCreate, onNewTask, autoMerge, onToggleAutoMerge, globalPaused, onUpdateTask, onArchiveTask, onUnarchiveTask, onArchiveAllDone, collapsed, onToggleCollapse }: ColumnProps) {
   const [dragOver, setDragOver] = useState(false);
   const [visibleTaskCount, setVisibleTaskCount] = useState(VISIBLE_TASKS_INITIAL);
   const countFlashing = useFlashOnIncrease(tasks.length);
@@ -99,6 +100,21 @@ function ColumnComponent({ column, tasks, maxConcurrent, onMoveTask, onOpenDetai
     setVisibleTaskCount((current) => Math.min(current + VISIBLE_TASKS_INCREMENT, tasks.length));
   }, [tasks.length]);
 
+  const handleArchiveAll = useCallback(async () => {
+    if (!onArchiveAllDone) return;
+    if (tasks.length === 0) return;
+
+    const confirmed = window.confirm(`Archive all ${tasks.length} done tasks?`);
+    if (!confirmed) return;
+
+    try {
+      const archived = await onArchiveAllDone();
+      addToast(`Archived ${archived.length} tasks`, "success");
+    } catch (err: any) {
+      addToast(err.message || "Failed to archive tasks", "error");
+    }
+  }, [onArchiveAllDone, tasks.length, addToast]);
+
   return (
     <div
       className={`column${dragOver ? " drag-over" : ""}${isArchived ? " column-archived" : ""}${isCollapsed ? " column-collapsed" : ""}`}
@@ -127,6 +143,17 @@ function ColumnComponent({ column, tasks, maxConcurrent, onMoveTask, onOpenDetai
             + New Task
           </button>
         )}
+        {column === "done" && onArchiveAllDone && (
+          <button
+            className="btn btn-icon btn-sm"
+            onClick={handleArchiveAll}
+            disabled={tasks.length === 0}
+            title="Archive all done tasks"
+            aria-label="Archive all done tasks"
+          >
+            <Archive size={16} />
+          </button>
+        )}
         {isArchived && onToggleCollapse && (
           <button
             className="btn btn-icon btn-sm"

packages/dashboard/app/hooks/__tests__/useTasks.test.ts

@@ -30,10 +30,14 @@ vi.mock("../../api", () => ({
   mergeTask: vi.fn(),
   retryTask: vi.fn(),
   updateTask: vi.fn(),
+  archiveTask: vi.fn(),
+  unarchiveTask: vi.fn(),
+  archiveAllDone: vi.fn(),
 }));
 
 const mockFetchTasks = vi.mocked(api.fetchTasks);
 const mockUpdateTask = vi.mocked(api.updateTask);
+const mockArchiveAllDone = vi.mocked(api.archiveAllDone);
 
 // Mock EventSource
 class MockEventSource {
@@ -643,4 +647,57 @@ describe("useTasks", () => {
       expect(result.current.tasks[0].dependencies).toEqual(["KB-002", "KB-003"]);
     });
   });
+
+  describe("archiveAllDone", () => {
+    it("archives all done tasks and updates local state", async () => {
+      const doneTasks = [
+        createMockTask({ id: "KB-001", column: "done" as Column }),
+        createMockTask({ id: "KB-002", column: "done" as Column }),
+      ];
+      const todoTask = createMockTask({ id: "KB-003", column: "todo" as Column });
+      mockFetchTasks.mockResolvedValueOnce([...doneTasks, todoTask]);
+
+      const archivedTasks = [
+        createMockTask({ id: "KB-001", column: "archived" as Column }),
+        createMockTask({ id: "KB-002", column: "archived" as Column }),
+      ];
+      mockArchiveAllDone.mockResolvedValueOnce(archivedTasks);
+
+      const { result } = renderHook(() => useTasks());
+
+      await waitFor(() => {
+        expect(result.current.tasks).toHaveLength(3);
+      });
+
+      await act(async () => {
+        await result.current.archiveAllDone();
+      });
+
+      expect(mockArchiveAllDone).toHaveBeenCalled();
+      // Done tasks should be archived
+      expect(result.current.tasks.find((t) => t.id === "KB-001")?.column).toBe("archived");
+      expect(result.current.tasks.find((t) => t.id === "KB-002")?.column).toBe("archived");
+      // Todo task should remain unchanged
+      expect(result.current.tasks.find((t) => t.id === "KB-003")?.column).toBe("todo");
+    });
+
+    it("returns empty array when no done tasks exist", async () => {
+      const todoTask = createMockTask({ id: "KB-001", column: "todo" as Column });
+      mockFetchTasks.mockResolvedValueOnce([todoTask]);
+      mockArchiveAllDone.mockResolvedValueOnce([]);
+
+      const { result } = renderHook(() => useTasks());
+
+      await waitFor(() => {
+        expect(result.current.tasks).toHaveLength(1);
+      });
+
+      const archived = await act(async () => {
+        return await result.current.archiveAllDone();
+      });
+
+      expect(archived).toEqual([]);
+      expect(result.current.tasks[0].column).toBe("todo");
+    });
+  });
 });

packages/dashboard/app/hooks/useTasks.ts

@@ -214,5 +214,18 @@ export function useTasks() {
     return task;
   }, []);
 
-  return { tasks, createTask, moveTask, deleteTask, mergeTask, retryTask, duplicateTask, updateTask, archiveTask, unarchiveTask };
+  const archiveAllDone = useCallback(async (): Promise<Task[]> => {
+    const archived = await api.archiveAllDone();
+    const normalized = archived.map(normalizeTask);
+    // Update local state by mapping over tasks and updating archived ones
+    setTasks((prev) =>
+      prev.map((t) => {
+        const updated = normalized.find((archived) => archived.id === t.id);
+        return updated || t;
+      })
+    );
+    return normalized;
+  }, []);
+
+  return { tasks, createTask, moveTask, deleteTask, mergeTask, retryTask, duplicateTask, updateTask, archiveTask, unarchiveTask, archiveAllDone };
 }

packages/dashboard/src/routes.test.ts

@@ -705,6 +705,63 @@ describe("POST /tasks/:id/unarchive", () => {
   });
 });
 
+describe("POST /tasks/archive-all-done", () => {
+  let store: TaskStore;
+
+  beforeEach(() => {
+    store = createMockStore({
+      archiveAllDone: vi.fn(),
+    });
+  });
+
+  function buildApp() {
+    const app = express();
+    app.use(express.json());
+    app.use("/api", createApiRoutes(store));
+    return app;
+  }
+
+  it("archives all done tasks and returns the archived array", async () => {
+    const archivedTasks = [
+      { ...FAKE_TASK_DETAIL, id: "KB-001", column: "archived" },
+      { ...FAKE_TASK_DETAIL, id: "KB-002", column: "archived" },
+    ];
+    (store.archiveAllDone as ReturnType<typeof vi.fn>).mockResolvedValue(archivedTasks);
+
+    const res = await REQUEST(buildApp(), "POST", "/api/tasks/archive-all-done", JSON.stringify({}), {
+      "Content-Type": "application/json",
+    });
+
+    expect(res.status).toBe(200);
+    expect(res.body.archived).toHaveLength(2);
+    expect(res.body.archived[0].column).toBe("archived");
+    expect(res.body.archived[1].column).toBe("archived");
+    expect(store.archiveAllDone).toHaveBeenCalled();
+  });
+
+  it("returns empty array when no done tasks exist", async () => {
+    (store.archiveAllDone as ReturnType<typeof vi.fn>).mockResolvedValue([]);
+
+    const res = await REQUEST(buildApp(), "POST", "/api/tasks/archive-all-done", JSON.stringify({}), {
+      "Content-Type": "application/json",
+    });
+
+    expect(res.status).toBe(200);
+    expect(res.body.archived).toEqual([]);
+  });
+
+  it("returns 500 on unexpected errors", async () => {
+    (store.archiveAllDone as ReturnType<typeof vi.fn>).mockRejectedValue(new Error("Database error"));
+
+    const res = await REQUEST(buildApp(), "POST", "/api/tasks/archive-all-done", JSON.stringify({}), {
+      "Content-Type": "application/json",
+    });
+
+    expect(res.status).toBe(500);
+    expect(res.body.error).toContain("Database error");
+  });
+});
+
 describe("PATCH /tasks/:id", () => {
   let store: TaskStore;
 

packages/dashboard/src/routes.ts

@@ -790,6 +790,16 @@ export function createApiRoutes(store: TaskStore, options?: ServerOptions): Rout
     }
   });
 
+  // Archive all done tasks
+  router.post("/tasks/archive-all-done", async (req, res) => {
+    try {
+      const archived = await store.archiveAllDone();
+      res.json({ archived });
+    } catch (err: any) {
+      res.status(500).json({ error: err.message });
+    }
+  });
+
   // Upload attachment
   router.post("/tasks/:id/attachments", upload.single("file"), async (req, res) => {
     try {