Add todo.ts (verbatim copy of upstream examples/extensions/todo.ts)

Provides the agent with a 'todo' tool (list/add/toggle/clear) and
registers /todos for the user. Useful for externalising multi-step
plans during long arcs.

State persists in tool result details rather than an external file,
which means: pi --continue brings todos back with the session, and
/fork forks the todo state along with the branch.

Copied not symlinked because the upstream path lives under a
homebrew-versioned Cellar dir that rotates on every pi upgrade.
Refresh procedure documented in AGENTS.md.

AGENTS.md

@@ -22,6 +22,7 @@ extensions/
   git-checkpoint.ts       # Git stash checkpoint per turn, restorable on /fork
   notify.ts               # Native terminal notification when agent finishes
   ext-toggle.ts           # /ext slash command — list & toggle extensions at runtime
+  todo.ts                 # `todo` tool for the agent + /todos for the user (copy of upstream example)
 install.sh                # Idempotent installer — symlinks extensions/ into ~/.pi/agent/extensions/
 package.json              # pi package manifest — enables `pi install /path` as an alternative
 README.md                 # User-facing docs.
@@ -220,6 +221,31 @@ session.
 
 No flags, no `agent_*` event handlers — fully passive until `/ext` is invoked.
 
+### `todo.ts`
+
+Unchanged copy of upstream `examples/extensions/todo.ts` from
+`pi-coding-agent` (the homebrew install at `/opt/homebrew/Cellar/...`).
+Provides the agent with a `todo` tool (actions: list/add/toggle/clear)
+and registers `/todos` for the user to inspect the list.
+
+**Why copied, not symlinked:** symlinking would point at
+`/opt/homebrew/Cellar/pi-coding-agent/<version>/libexec/...` which
+rotates on every brew upgrade — fragile. Copy keeps it stable; we lose
+upstream updates but gain reproducibility.
+
+**State persistence:** the agent stores todo state in tool result
+`details`, not an external file. Two useful properties: state survives
+`pi --continue`/`--resume` because it lives in the session JSONL, and
+`/fork` correctly forks the todo list along with the conversation.
+
+**Refresh from upstream when needed:**
+
+```bash
+cp /opt/homebrew/Cellar/pi-coding-agent/*/libexec/lib/node_modules/@mariozechner/pi-coding-agent/examples/extensions/todo.ts \
+   ~/src/src_local/pi-extensions/extensions/todo.ts
+# review diff, then commit
+```
+
 No framework. Manual:
 
 ```bash

README.md

@@ -193,6 +193,16 @@ A footer line shows pending changes (e.g. `pending: notify→off, foo→on`) so
 3. In a running pi session, `/reload` is enough; no restart needed
 4. (or, with `ext-toggle` installed: `/ext` to disable noisy ones at runtime)
 
+### `todo.ts`
+
+Gives the agent a `todo` tool (actions: `list` / `add` / `toggle` / `clear`) so it can externalize a multi-step plan and tick items off as it works. Also registers `/todos` so you can inspect the current list at any time.
+
+State lives in the session's tool result `details`, not an external file. So:
+- `pi --continue` / `--resume` brings the todos back with the conversation.
+- `/fork` forks the todo list along with the branch — each branch has its own state.
+
+This is a verbatim copy of the upstream `examples/extensions/todo.ts` shipped with `pi-coding-agent`. Refresh from upstream when desired (see `AGENTS.md`).
+
 Each extension is a TypeScript module loaded by [jiti](https://github.com/unjs/jiti) — no compilation step. See the [pi extensions docs](https://github.com/mariozechner/pi-coding-agent/blob/main/docs/extensions.md) and the [built-in examples](https://github.com/mariozechner/pi-coding-agent/tree/main/examples/extensions) for the API surface.
 
 ---

extensions/todo.ts

@@ -0,0 +1,297 @@
+/**
+ * Todo Extension - Demonstrates state management via session entries
+ *
+ * This extension:
+ * - Registers a `todo` tool for the LLM to manage todos
+ * - Registers a `/todos` command for users to view the list
+ *
+ * State is stored in tool result details (not external files), which allows
+ * proper branching - when you branch, the todo state is automatically
+ * correct for that point in history.
+ */
+
+import { StringEnum } from "@mariozechner/pi-ai";
+import type { ExtensionAPI, ExtensionContext, Theme } from "@mariozechner/pi-coding-agent";
+import { matchesKey, Text, truncateToWidth } from "@mariozechner/pi-tui";
+import { Type } from "typebox";
+
+interface Todo {
+	id: number;
+	text: string;
+	done: boolean;
+}
+
+interface TodoDetails {
+	action: "list" | "add" | "toggle" | "clear";
+	todos: Todo[];
+	nextId: number;
+	error?: string;
+}
+
+const TodoParams = Type.Object({
+	action: StringEnum(["list", "add", "toggle", "clear"] as const),
+	text: Type.Optional(Type.String({ description: "Todo text (for add)" })),
+	id: Type.Optional(Type.Number({ description: "Todo ID (for toggle)" })),
+});
+
+/**
+ * UI component for the /todos command
+ */
+class TodoListComponent {
+	private todos: Todo[];
+	private theme: Theme;
+	private onClose: () => void;
+	private cachedWidth?: number;
+	private cachedLines?: string[];
+
+	constructor(todos: Todo[], theme: Theme, onClose: () => void) {
+		this.todos = todos;
+		this.theme = theme;
+		this.onClose = onClose;
+	}
+
+	handleInput(data: string): void {
+		if (matchesKey(data, "escape") || matchesKey(data, "ctrl+c")) {
+			this.onClose();
+		}
+	}
+
+	render(width: number): string[] {
+		if (this.cachedLines && this.cachedWidth === width) {
+			return this.cachedLines;
+		}
+
+		const lines: string[] = [];
+		const th = this.theme;
+
+		lines.push("");
+		const title = th.fg("accent", " Todos ");
+		const headerLine =
+			th.fg("borderMuted", "─".repeat(3)) + title + th.fg("borderMuted", "─".repeat(Math.max(0, width - 10)));
+		lines.push(truncateToWidth(headerLine, width));
+		lines.push("");
+
+		if (this.todos.length === 0) {
+			lines.push(truncateToWidth(`  ${th.fg("dim", "No todos yet. Ask the agent to add some!")}`, width));
+		} else {
+			const done = this.todos.filter((t) => t.done).length;
+			const total = this.todos.length;
+			lines.push(truncateToWidth(`  ${th.fg("muted", `${done}/${total} completed`)}`, width));
+			lines.push("");
+
+			for (const todo of this.todos) {
+				const check = todo.done ? th.fg("success", "✓") : th.fg("dim", "○");
+				const id = th.fg("accent", `#${todo.id}`);
+				const text = todo.done ? th.fg("dim", todo.text) : th.fg("text", todo.text);
+				lines.push(truncateToWidth(`  ${check} ${id} ${text}`, width));
+			}
+		}
+
+		lines.push("");
+		lines.push(truncateToWidth(`  ${th.fg("dim", "Press Escape to close")}`, width));
+		lines.push("");
+
+		this.cachedWidth = width;
+		this.cachedLines = lines;
+		return lines;
+	}
+
+	invalidate(): void {
+		this.cachedWidth = undefined;
+		this.cachedLines = undefined;
+	}
+}
+
+export default function (pi: ExtensionAPI) {
+	// In-memory state (reconstructed from session on load)
+	let todos: Todo[] = [];
+	let nextId = 1;
+
+	/**
+	 * Reconstruct state from session entries.
+	 * Scans tool results for this tool and applies them in order.
+	 */
+	const reconstructState = (ctx: ExtensionContext) => {
+		todos = [];
+		nextId = 1;
+
+		for (const entry of ctx.sessionManager.getBranch()) {
+			if (entry.type !== "message") continue;
+			const msg = entry.message;
+			if (msg.role !== "toolResult" || msg.toolName !== "todo") continue;
+
+			const details = msg.details as TodoDetails | undefined;
+			if (details) {
+				todos = details.todos;
+				nextId = details.nextId;
+			}
+		}
+	};
+
+	// Reconstruct state on session events
+	pi.on("session_start", async (_event, ctx) => reconstructState(ctx));
+	pi.on("session_tree", async (_event, ctx) => reconstructState(ctx));
+
+	// Register the todo tool for the LLM
+	pi.registerTool({
+		name: "todo",
+		label: "Todo",
+		description: "Manage a todo list. Actions: list, add (text), toggle (id), clear",
+		parameters: TodoParams,
+
+		async execute(_toolCallId, params, _signal, _onUpdate, _ctx) {
+			switch (params.action) {
+				case "list":
+					return {
+						content: [
+							{
+								type: "text",
+								text: todos.length
+									? todos.map((t) => `[${t.done ? "x" : " "}] #${t.id}: ${t.text}`).join("\n")
+									: "No todos",
+							},
+						],
+						details: { action: "list", todos: [...todos], nextId } as TodoDetails,
+					};
+
+				case "add": {
+					if (!params.text) {
+						return {
+							content: [{ type: "text", text: "Error: text required for add" }],
+							details: { action: "add", todos: [...todos], nextId, error: "text required" } as TodoDetails,
+						};
+					}
+					const newTodo: Todo = { id: nextId++, text: params.text, done: false };
+					todos.push(newTodo);
+					return {
+						content: [{ type: "text", text: `Added todo #${newTodo.id}: ${newTodo.text}` }],
+						details: { action: "add", todos: [...todos], nextId } as TodoDetails,
+					};
+				}
+
+				case "toggle": {
+					if (params.id === undefined) {
+						return {
+							content: [{ type: "text", text: "Error: id required for toggle" }],
+							details: { action: "toggle", todos: [...todos], nextId, error: "id required" } as TodoDetails,
+						};
+					}
+					const todo = todos.find((t) => t.id === params.id);
+					if (!todo) {
+						return {
+							content: [{ type: "text", text: `Todo #${params.id} not found` }],
+							details: {
+								action: "toggle",
+								todos: [...todos],
+								nextId,
+								error: `#${params.id} not found`,
+							} as TodoDetails,
+						};
+					}
+					todo.done = !todo.done;
+					return {
+						content: [{ type: "text", text: `Todo #${todo.id} ${todo.done ? "completed" : "uncompleted"}` }],
+						details: { action: "toggle", todos: [...todos], nextId } as TodoDetails,
+					};
+				}
+
+				case "clear": {
+					const count = todos.length;
+					todos = [];
+					nextId = 1;
+					return {
+						content: [{ type: "text", text: `Cleared ${count} todos` }],
+						details: { action: "clear", todos: [], nextId: 1 } as TodoDetails,
+					};
+				}
+
+				default:
+					return {
+						content: [{ type: "text", text: `Unknown action: ${params.action}` }],
+						details: {
+							action: "list",
+							todos: [...todos],
+							nextId,
+							error: `unknown action: ${params.action}`,
+						} as TodoDetails,
+					};
+			}
+		},
+
+		renderCall(args, theme, _context) {
+			let text = theme.fg("toolTitle", theme.bold("todo ")) + theme.fg("muted", args.action);
+			if (args.text) text += ` ${theme.fg("dim", `"${args.text}"`)}`;
+			if (args.id !== undefined) text += ` ${theme.fg("accent", `#${args.id}`)}`;
+			return new Text(text, 0, 0);
+		},
+
+		renderResult(result, { expanded }, theme, _context) {
+			const details = result.details as TodoDetails | undefined;
+			if (!details) {
+				const text = result.content[0];
+				return new Text(text?.type === "text" ? text.text : "", 0, 0);
+			}
+
+			if (details.error) {
+				return new Text(theme.fg("error", `Error: ${details.error}`), 0, 0);
+			}
+
+			const todoList = details.todos;
+
+			switch (details.action) {
+				case "list": {
+					if (todoList.length === 0) {
+						return new Text(theme.fg("dim", "No todos"), 0, 0);
+					}
+					let listText = theme.fg("muted", `${todoList.length} todo(s):`);
+					const display = expanded ? todoList : todoList.slice(0, 5);
+					for (const t of display) {
+						const check = t.done ? theme.fg("success", "✓") : theme.fg("dim", "○");
+						const itemText = t.done ? theme.fg("dim", t.text) : theme.fg("muted", t.text);
+						listText += `\n${check} ${theme.fg("accent", `#${t.id}`)} ${itemText}`;
+					}
+					if (!expanded && todoList.length > 5) {
+						listText += `\n${theme.fg("dim", `... ${todoList.length - 5} more`)}`;
+					}
+					return new Text(listText, 0, 0);
+				}
+
+				case "add": {
+					const added = todoList[todoList.length - 1];
+					return new Text(
+						theme.fg("success", "✓ Added ") +
+							theme.fg("accent", `#${added.id}`) +
+							" " +
+							theme.fg("muted", added.text),
+						0,
+						0,
+					);
+				}
+
+				case "toggle": {
+					const text = result.content[0];
+					const msg = text?.type === "text" ? text.text : "";
+					return new Text(theme.fg("success", "✓ ") + theme.fg("muted", msg), 0, 0);
+				}
+
+				case "clear":
+					return new Text(theme.fg("success", "✓ ") + theme.fg("muted", "Cleared all todos"), 0, 0);
+			}
+		},
+	});
+
+	// Register the /todos command for users
+	pi.registerCommand("todos", {
+		description: "Show all todos on the current branch",
+		handler: async (_args, ctx) => {
+			if (!ctx.hasUI) {
+				ctx.ui.notify("/todos requires interactive mode", "error");
+				return;
+			}
+
+			await ctx.ui.custom<void>((_tui, theme, _kb, done) => {
+				return new TodoListComponent(todos, theme, () => done());
+			});
+		},
+	});
+}