feat(todo): port opencode's declarative whole-list todo tool

Replace the imperative id-based CRUD todo tool (add/update/list/get/remove)
with opencode's declarative whole-list design: a single `todos` param that
replaces the entire list each call. No model-visible ids, no delta reasoning,
no "task not found" spirals.

- core: TaskItem { id, content, status }; statuses pending|in_progress|
  completed|cancelled. TaskList.setTasks/getTasks/onChange. New rich
  TODO_DESCRIPTION adapted from opencode's todowrite.txt.
- api: TASK_MANAGEMENT_GUIDANCE system-prompt section (from anthropic.txt);
  updated TOOL_DESCRIPTIONS.todo. Reload fix: TabStatusSnapshot now carries
  per-tab tasks so getAllStatuses rehydrates the panel on reconnect.
- frontend: mirror types; hydrate tasks from snapshot in both restore paths;
  upgrade sidebar Tasks panel to render content + all four statuses + progress.
- tests: new core task-list.test.ts (15); updated api TaskList mocks +
  getAllStatuses task-snapshot coverage.

bun run check clean; 569 tests pass; all packages typecheck.

2 files changed, 50 insertions, 32 deletions

diff --git a/packages/api/tests/agent-manager.test.ts b/packages/api/tests/agent-manager.test.ts
index 9da6a70..014022a 100644
--- a/packages/api/tests/agent-manager.test.ts
+++ b/packages/api/tests/agent-manager.test.ts
@@ -279,20 +279,17 @@ vi.mock("@dispatch/core", () => ({
 		}
 	},
 	TaskList: class MockTaskList {
+		private tasks: Array<{ id: string; content: string; status: string }> = [];
 		getTasks() {
-			return [];
-		}
-		getTask() {
-			return undefined;
-		}
-		addTask() {
-			return { id: "task-1", title: "", description: "", status: "pending" };
-		}
-		updateTask() {
-			return undefined;
+			return this.tasks.map((t) => ({ ...t }));
 		}
-		removeTask() {
-			return false;
+		setTasks(items: Array<{ content: string; status?: string }>) {
+			this.tasks = items.map((item, i) => ({
+				id: `task-${i + 1}`,
+				content: item.content,
+				status: item.status ?? "pending",
+			}));
+			return this.getTasks();
 		}
 		onChange(_cb: unknown) {
 			return () => {};
@@ -907,7 +904,7 @@ describe("AgentManager", () => {
 					status: "running" | "idle" | "error";
 					keyId: null;
 					modelId: null;
-					taskList: { onChange: (cb: unknown) => void };
+					taskList: { onChange: (cb: unknown) => void; getTasks: () => unknown[] };
 					messageQueue: unknown[];
 					queueListeners: unknown[];
 					shellStore: unknown;
@@ -922,7 +919,7 @@ describe("AgentManager", () => {
 			status: "running",
 			keyId: null,
 			modelId: null,
-			taskList: { onChange: () => {} },
+			taskList: { onChange: () => {}, getTasks: () => [] },
 			messageQueue: [],
 			queueListeners: [],
 			shellStore: {},
@@ -954,7 +951,7 @@ describe("AgentManager", () => {
 					status: "running";
 					keyId: null;
 					modelId: null;
-					taskList: { onChange: (cb: unknown) => void };
+					taskList: { onChange: (cb: unknown) => void; getTasks: () => unknown[] };
 					messageQueue: unknown[];
 					queueListeners: unknown[];
 					shellStore: unknown;
@@ -970,7 +967,7 @@ describe("AgentManager", () => {
 			status: "running",
 			keyId: null,
 			modelId: null,
-			taskList: { onChange: () => {} },
+			taskList: { onChange: () => {}, getTasks: () => [] },
 			messageQueue: [],
 			queueListeners: [],
 			shellStore: {},
@@ -996,7 +993,7 @@ describe("AgentManager", () => {
 					status: "running";
 					keyId: null;
 					modelId: null;
-					taskList: { onChange: (cb: unknown) => void };
+					taskList: { onChange: (cb: unknown) => void; getTasks: () => unknown[] };
 					messageQueue: unknown[];
 					queueListeners: unknown[];
 					shellStore: unknown;
@@ -1011,7 +1008,7 @@ describe("AgentManager", () => {
 			status: "running",
 			keyId: null,
 			modelId: null,
-			taskList: { onChange: () => {} },
+			taskList: { onChange: () => {}, getTasks: () => [] },
 			messageQueue: [],
 			queueListeners: [],
 			shellStore: {},
@@ -1026,6 +1023,30 @@ describe("AgentManager", () => {
 		expect(snap["tab-early"]).not.toHaveProperty("currentAssistantId");
 	});
 
+	it("getAllStatuses includes a tab's todo list (for reload rehydration)", () => {
+		const manager = new AgentManager();
+		// Public API: getTaskList creates+returns the tab's list. setTasks is
+		// the declarative whole-list write.
+		const list = manager.getTaskList("tab-todos");
+		list.setTasks([
+			{ content: "plan", status: "completed" },
+			{ content: "build", status: "in_progress" },
+		]);
+		const snap = manager.getAllStatuses();
+		expect(snap["tab-todos"]?.tasks).toEqual([
+			{ id: "task-1", content: "plan", status: "completed" },
+			{ id: "task-2", content: "build", status: "in_progress" },
+		]);
+	});
+
+	it("getAllStatuses omits tasks for a tab with an empty todo list", () => {
+		const manager = new AgentManager();
+		manager.getTaskList("tab-empty");
+		const snap = manager.getAllStatuses();
+		expect(snap["tab-empty"]).toBeDefined();
+		expect(snap["tab-empty"]).not.toHaveProperty("tasks");
+	});
+
 	// ─── Tab-to-tab communication ─────────────────────────────────
 
 	describe("deliverMessage", () => {
@@ -1054,7 +1075,7 @@ describe("AgentManager", () => {
 				status: "running",
 				keyId: null,
 				modelId: null,
-				taskList: { onChange: () => {} },
+				taskList: { onChange: () => {}, getTasks: () => [] },
 				messageQueue: [],
 				queueListeners: [],
 				shellStore: {},
@@ -1175,7 +1196,7 @@ describe("AgentManager", () => {
 				status: "running",
 				keyId: null,
 				modelId: null,
-				taskList: { onChange: () => {} },
+				taskList: { onChange: () => {}, getTasks: () => [] },
 				messageQueue: [],
 				queueListeners: [],
 				shellStore: {},
diff --git a/packages/api/tests/routes.test.ts b/packages/api/tests/routes.test.ts
index c1971b0..a8db5ce 100644
--- a/packages/api/tests/routes.test.ts
+++ b/packages/api/tests/routes.test.ts
@@ -140,20 +140,17 @@ vi.mock("@dispatch/core", () => ({
 		}
 	},
 	TaskList: class MockTaskList {
+		private tasks: Array<{ id: string; content: string; status: string }> = [];
 		getTasks() {
-			return [];
-		}
-		getTask() {
-			return undefined;
-		}
-		addTask() {
-			return { id: "task-1", title: "", description: "", status: "pending" };
+			return this.tasks.map((t) => ({ ...t }));
 		}
-		updateTask() {
-			return undefined;
-		}
-		removeTask() {
-			return false;
+		setTasks(items: Array<{ content: string; status?: string }>) {
+			this.tasks = items.map((item, i) => ({
+				id: `task-${i + 1}`,
+				content: item.content,
+				status: item.status ?? "pending",
+			}));
+			return this.getTasks();
 		}
 		onChange(_cb: unknown) {
 			return () => {};