diff --git a/apps/cli/src/application/assistant/reminders/manager.ts b/apps/cli/src/application/assistant/reminders/manager.ts
new file mode 100644
index 00000000..cd0d42b6
--- /dev/null
+++ b/apps/cli/src/application/assistant/reminders/manager.ts
@@ -0,0 +1,104 @@
+import * as fs from "fs/promises";
+import * as path from "path";
+import { CopilotDataDir } from "../../config/config.js";
+import { buildTodoReminder, readTodoState } from "../../lib/todo-store.js";
+
+const REMINDERS_FILE = path.join(CopilotDataDir, "reminders.json");
+
+type ReminderState = {
+    lastSent: Record<string, string>;
+    lastTodoToolUse?: string;
+};
+
+const defaultState: ReminderState = {
+    lastSent: {},
+};
+
+const TODO_TOOL_NAMES = new Set(["todoList", "todoWrite", "todoUpdate"]);
+
+const ReminderCooldownMs: Record<string, number> = {
+    "todo-empty": 15 * 60 * 1000,
+    "todo-review": 10 * 60 * 1000,
+};
+
+const TodoEngagementThresholdMs = 10 * 60 * 1000; // remind if todo tools unused for 10+ minutes while todos exist
+
+async function loadState(): Promise<ReminderState> {
+    try {
+        const raw = await fs.readFile(REMINDERS_FILE, "utf-8");
+        const parsed = JSON.parse(raw);
+        return {
+            lastSent: typeof parsed.lastSent === "object" && parsed.lastSent !== null ? parsed.lastSent : {},
+            lastTodoToolUse: typeof parsed.lastTodoToolUse === "string" ? parsed.lastTodoToolUse : undefined,
+        };
+    } catch {
+        return { ...defaultState };
+    }
+}
+
+async function saveState(state: ReminderState) {
+    await fs.mkdir(path.dirname(REMINDERS_FILE), { recursive: true });
+    await fs.writeFile(REMINDERS_FILE, JSON.stringify(state, null, 2), "utf-8");
+}
+
+function shouldSend(state: ReminderState, key: string): boolean {
+    const cooldown = ReminderCooldownMs[key] ?? 5 * 60 * 1000;
+    const lastSent = state.lastSent[key];
+    if (!lastSent) return true;
+    const elapsed = Date.now() - new Date(lastSent).getTime();
+    return elapsed >= cooldown;
+}
+
+export type ReminderContext = {
+    source: "tool-result" | "message";
+    toolName?: string;
+};
+
+export async function collectSystemReminders(context: ReminderContext): Promise<string[]> {
+    const state = await loadState();
+    let hasStateChanges = false;
+    const reminders: string[] = [];
+    const now = new Date().toISOString();
+
+    if (context.toolName && TODO_TOOL_NAMES.has(context.toolName)) {
+        if (state.lastTodoToolUse !== now) {
+            state.lastTodoToolUse = now;
+            hasStateChanges = true;
+        }
+    } else {
+        reminders.push(...await maybeAddTodoReminders(state, context));
+        if (reminders.length > 0) {
+            // maybeAddTodoReminders updates state timestamps internally
+            hasStateChanges = true;
+        }
+    }
+
+    if (hasStateChanges) {
+        await saveState(state);
+    }
+
+    return reminders;
+}
+
+async function maybeAddTodoReminders(state: ReminderState, context: ReminderContext): Promise<string[]> {
+    const reminders: string[] = [];
+    const todoState = await readTodoState();
+    const nowIso = new Date().toISOString();
+
+    if (todoState.todos.length === 0) {
+        if (shouldSend(state, "todo-empty")) {
+            reminders.push(buildTodoReminder(todoState.todos, "This is a private reminder: your todo list is empty. If the current work benefits from tracking progress, use the TodoWrite tool to outline the plan."));
+            state.lastSent["todo-empty"] = nowIso;
+        }
+        return reminders;
+    }
+
+    const lastUseTs = state.lastTodoToolUse ? new Date(state.lastTodoToolUse).getTime() : 0;
+    const todoStale = Date.now() - lastUseTs >= TodoEngagementThresholdMs;
+    if (todoStale && shouldSend(state, "todo-review")) {
+        reminders.push(buildTodoReminder(todoState.todos, "Private reminder: review and update your todo list as you make progress. Keep this reminder internal and reflect updates via the todo tools."));
+        state.lastSent["todo-review"] = nowIso;
+    }
+
+    return reminders;
+}
diff --git a/apps/cli/src/application/lib/todo-store.ts b/apps/cli/src/application/lib/todo-store.ts
new file mode 100644
index 00000000..80594a0a
--- /dev/null
+++ b/apps/cli/src/application/lib/todo-store.ts
@@ -0,0 +1,76 @@
+import { z } from "zod";
+
+export const TodoStatusSchema = z.enum(["pending", "in_progress", "done", "blocked"]);
+
+export type TodoStatus = z.infer<typeof TodoStatusSchema>;
+
+export type TodoItem = {
+    id: string;
+    content: string;
+    status: TodoStatus;
+};
+
+export type TodoState = {
+    todos: TodoItem[];
+    updatedAt: string;
+};
+
+const defaultTodoState: TodoState = {
+    todos: [],
+    updatedAt: new Date(0).toISOString(),
+};
+
+const todoStateStack: TodoState[] = [{ ...defaultTodoState }];
+
+const currentState = (): TodoState => todoStateStack[todoStateStack.length - 1];
+
+export async function readTodoState(): Promise<TodoState> {
+    return currentState();
+}
+
+export async function writeTodoState(todos: TodoItem[]): Promise<TodoState> {
+    const updated = {
+        todos: sanitiseTodos(todos),
+        updatedAt: new Date().toISOString(),
+    };
+    todoStateStack[todoStateStack.length - 1] = updated;
+    return updated;
+}
+
+export function resetTodoState(): void {
+    todoStateStack[todoStateStack.length - 1] = { ...defaultTodoState };
+}
+
+export function pushTodoState(initialState?: TodoState): void {
+    todoStateStack.push(initialState ? { ...initialState } : { ...defaultTodoState });
+}
+
+export function popTodoState(): void {
+    if (todoStateStack.length > 1) {
+        todoStateStack.pop();
+    } else {
+        todoStateStack[0] = { ...defaultTodoState };
+    }
+}
+
+export function sanitiseTodos(todos: TodoItem[]): TodoItem[] {
+    const seen = new Set<string>();
+    const sanitized: TodoItem[] = [];
+    for (const todo of todos) {
+        if (!todo) continue;
+        const id = typeof todo.id === "string" ? todo.id.trim() : "";
+        const content = typeof todo.content === "string" ? todo.content : "";
+        const statusResult = TodoStatusSchema.safeParse(todo.status);
+        const status = statusResult.success ? statusResult.data : "pending";
+        if (!id || !content || seen.has(id)) {
+            continue;
+        }
+        seen.add(id);
+        sanitized.push({ id, content, status });
+    }
+    return sanitized;
+}
+
+export function buildTodoReminder(todos: TodoItem[], preface: string) {
+    return `<system-reminder>\n${preface}\n\n${JSON.stringify(todos)}\n</system-reminder>`;
+}