feat(KB-016): add task duplicate command

- Add duplicateTask() method to core store with fresh state reset
- Add CLI command handler and register duplicate subcommand
- Add POST /tasks/:id/duplicate API endpoint to dashboard
- Add comprehensive tests for store, CLI, and API routes
- Add pi extension tool for task duplication
- Add changeset for minor release bump

packages/cli/src/__tests__/extension.test.ts

@@ -80,6 +80,7 @@ describe("kb pi extension", () => {
         "kb_task_attach",
         "kb_task_pause",
         "kb_task_unpause",
+        "kb_task_duplicate",
         "kb_task_import_github",
         "kb_task_import_github_issue",
         "kb_task_browse_github_issues",

packages/cli/src/bin.ts

@@ -39,7 +39,7 @@ if (isBunBinary) {
 
 // Dynamic imports so the pi-coding-agent config module sees PI_PACKAGE_DIR
 const { runDashboard } = await import("./commands/dashboard.js");
-const { runTaskCreate, runTaskList, runTaskMove, runTaskMerge, runTaskUpdate, runTaskLog, runTaskShow, runTaskAttach, runTaskPause, runTaskUnpause, runTaskImportFromGitHub } = await import("./commands/task.js");
+const { runTaskCreate, runTaskList, runTaskMove, runTaskMerge, runTaskUpdate, runTaskLog, runTaskShow, runTaskAttach, runTaskPause, runTaskUnpause, runTaskImportFromGitHub, runTaskDuplicate } = await import("./commands/task.js");
 
 const HELP = `
 kb — AI-orchestrated task board
@@ -54,6 +54,7 @@ Usage:
   kb task update <id> <step> <status> Update step status (pending|in-progress|done|skipped)
   kb task log <id> <message>          Add a log entry
   kb task merge <id>                  Merge an in-review task and close it
+  kb task duplicate <id>              Duplicate a task (creates copy in triage)
   kb task attach <id> <file>          Attach a file to a task
   kb task pause <id>                  Pause a task (stops all automation)
   kb task unpause <id>                Unpause a task (resumes automation)
@@ -164,6 +165,12 @@ async function main() {
             await runTaskMerge(id);
             break;
           }
+          case "duplicate": {
+            const id = args[2];
+            if (!id) { console.error("Usage: kb task duplicate <id>"); process.exit(1); }
+            await runTaskDuplicate(id);
+            break;
+          }
           case "attach": {
             const id = args[2], file = args[3];
             if (!id || !file) {

packages/cli/src/commands/task.test.ts

@@ -28,7 +28,7 @@ vi.mock("@kb/engine", () => ({ aiMergeTask: vi.fn() }));
 
 import { createInterface } from "node:readline/promises";
 import { TaskStore } from "@kb/core";
-import { runTaskShow, runTaskCreate } from "./task.js";
+import { runTaskShow, runTaskCreate, runTaskDuplicate } from "./task.js";
 
 function makeTask(overrides: Record<string, unknown> = {}) {
   return {
@@ -838,3 +838,57 @@ describe("runTaskImportFromGitHub", () => {
     });
   });
 });
+
+// --- Duplicate Tests ---
+
+describe("runTaskDuplicate", () => {
+  let logSpy: ReturnType<typeof vi.spyOn>;
+  let errorSpy: ReturnType<typeof vi.spyOn>;
+  let mockDuplicateTask: ReturnType<typeof vi.fn>;
+
+  beforeEach(() => {
+    logSpy = vi.spyOn(console, "log").mockImplementation(() => {});
+    errorSpy = vi.spyOn(console, "error").mockImplementation(() => {});
+
+    mockDuplicateTask = vi.fn().mockResolvedValue({
+      id: "KB-002",
+      description: "Duplicated task",
+      column: "triage",
+      dependencies: [],
+      steps: [],
+      currentStep: 0,
+      log: [],
+      createdAt: new Date().toISOString(),
+      updatedAt: new Date().toISOString(),
+    });
+
+    (TaskStore as unknown as ReturnType<typeof vi.fn>).mockImplementation(() => ({
+      init: vi.fn(),
+      duplicateTask: mockDuplicateTask,
+    }));
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it("duplicates task and prints success", async () => {
+    await runTaskDuplicate("KB-001");
+
+    expect(mockDuplicateTask).toHaveBeenCalledOnce();
+    expect(mockDuplicateTask).toHaveBeenCalledWith("KB-001");
+
+    const successLine = logSpy.mock.calls.find(
+      (call) => typeof call[0] === "string" && call[0].includes("✓ Duplicated"),
+    );
+    expect(successLine).toBeDefined();
+    expect(successLine![0]).toContain("KB-001");
+    expect(successLine![0]).toContain("KB-002");
+  });
+
+  it("throws when task not found", async () => {
+    mockDuplicateTask.mockRejectedValueOnce(new Error("Task KB-999 not found"));
+
+    await expect(runTaskDuplicate("KB-999")).rejects.toThrow("Task KB-999 not found");
+  });
+});

packages/cli/src/commands/task.ts

@@ -286,6 +286,16 @@ export async function runTaskMove(id: string, column: string) {
   console.log();
 }
 
+export async function runTaskDuplicate(id: string) {
+  const store = await getStore();
+  const newTask = await store.duplicateTask(id);
+
+  console.log();
+  console.log(`  ✓ Duplicated ${id} → ${newTask.id}`);
+  console.log(`    Path: .kb/tasks/${newTask.id}/`);
+  console.log();
+}
+
 export async function runTaskImportGitHubInteractive(
   ownerRepo: string,
   options: TaskImportOptions = {}

packages/cli/src/extension.ts

@@ -341,6 +341,36 @@ export default function kbExtension(pi: ExtensionAPI) {
     },
   });
 
+  // ── kb_task_duplicate ─────────────────────────────────────────────
+
+  pi.registerTool({
+    name: "kb_task_duplicate",
+    label: "KB: Duplicate Task",
+    description:
+      "Duplicate an existing task, creating a fresh copy in triage. " +
+      "Copies the title and description but resets all execution state. " +
+      "The AI triage agent will re-specify the new task.",
+    promptSnippet: "Duplicate a kb task (creates copy in triage)",
+    promptGuidelines: [
+      "Use when a task needs to be re-done, split, or used as a template",
+      "The duplicated task will be placed in triage for re-specification",
+      "Dependencies, attachments, and execution state are NOT copied",
+    ],
+    parameters: Type.Object({
+      id: Type.String({ description: "Source task ID to duplicate (e.g. KB-001)" }),
+    }),
+
+    async execute(_toolCallId, params, _signal, _onUpdate, ctx) {
+      const store = await getStore(ctx.cwd);
+      const newTask = await store.duplicateTask(params.id);
+
+      return {
+        content: [{ type: "text", text: `Duplicated ${params.id} → ${newTask.id}` }],
+        details: { sourceId: params.id, newTaskId: newTask.id },
+      };
+    },
+  });
+
   // ── kb_task_import_github ─────────────────────────────────────────
 
   pi.registerTool({