diff --git a/packages/coding-agent/src/experimental/vacation/README.md b/packages/coding-agent/src/experimental/vacation/README.md
new file mode 100644
index 000000000..82ec2c03c
--- /dev/null
+++ b/packages/coding-agent/src/experimental/vacation/README.md
@@ -0,0 +1,53 @@
+# vacation
+
+A durable vacation planning agent with a TUI, built on `@earendil-works/pi-durable`. It is a copy of the durable coding
+agent in [`../durable`](../durable) with the coding tools and pi's coding prompt replaced by a vacation planner. It only
+looks like a coding agent because it reuses pi's interactive TUI components.
+
+From a pi checkout, after `npm install` and `npm run build`:
+
+```bash
+node packages/coding-agent/src/experimental/vacation/main.ts
+node packages/coding-agent/src/experimental/vacation/main.ts --continue
+```
+
+Without a build, preload the source resolver so the workspace packages load from `src` instead of `dist`:
+
+```bash
+node --import ./packages/coding-agent/src/experimental/source-resolver.ts packages/coding-agent/src/experimental/vacation/main.ts
+```
+
+A new session starts with pi's default model and thinking level from `settings.json`. `--continue` opens the newest
+session for the current directory. Sessions live under
+`~/.pi/agent/experimental/vacation-sessions/<cwd-hash>/<session>/session.sqlite`. Log in with pi itself; credentials are
+shared.
+
+## What it shows
+
+- **Background subagent:** the `research` tool starts a subagent in its own conversation and returns at once. A
+  background task delivers the request and posts the subagent's report back to the main conversation as a new message,
+  so you keep chatting with the main agent while the research runs.
+- **Parallel durable tool calls:** the subagent's `search` calls run in parallel, each as its own task in the task
+  panel. The results are canned; each topic takes a different time.
+- **Recovery:** `search` is safe to rerun. Kill the process while a search runs and start it again with `--continue`:
+  finished searches are kept, the unfinished one runs again, and the report still arrives. Request IDs keep a restart
+  from sending the request or the report twice.
+- **Everything else from the durable coding agent:** steering, follow-ups, `/agents`, `/compact`, `/tasks`, `/model`.
+
+## Try it
+
+1. "Plan a weekend in Vienna for two. Hand the research to a subagent."
+2. While the searches run, ask the main agent something else.
+3. Ctrl+C while only the trains search is left, then start again with `--continue`.
+4. `/agents` to watch or steer the subagent, `/agents` again to go back to main.
+
+## Layout
+
+| file | role |
+| --- | --- |
+| `vacation.ts` | the vacation extensions: `search`, `research`, the report task, and the prompt |
+| `main.ts` | arguments, open, run, close |
+| `sessions.ts` | session directories and the lock |
+| `harness-setup.ts` | HTTP setup, settings, the registry, the initial model |
+| `runtime.ts` | Harness and the plain `DurableView` and `DurableController` |
+| `tui.ts` | rendering with pi's interactive components |
diff --git a/packages/coding-agent/src/experimental/vacation/harness-setup.ts b/packages/coding-agent/src/experimental/vacation/harness-setup.ts
new file mode 100644
index 000000000..bffa15ee5
--- /dev/null
+++ b/packages/coding-agent/src/experimental/vacation/harness-setup.ts
@@ -0,0 +1,89 @@
+import type { ModelThinkingLevel } from "@earendil-works/pi-ai";
+import { createRegistry, type HarnessSettings, type ModelRef, type Registry } from "@earendil-works/pi-durable";
+import { applyHttpProxySettings, configureHttpDispatcher } from "../../core/http-dispatcher.ts";
+import { findInitialModel, resolveCliModel } from "../../core/model-resolver.ts";
+import type { ModelRuntime } from "../../core/model-runtime.ts";
+import type { SettingsManager } from "../../core/settings-manager.ts";
+import { Search, Vacation } from "./vacation.ts";
+
+/** pi's HTTP setup: proxy, idle timeouts, and one undici for fetch. Without it, some provider streams break off. */
+export function configureHarnessHttp(settingsManager: SettingsManager): void {
+	applyHttpProxySettings(settingsManager.getGlobalSettings().httpProxy);
+	configureHttpDispatcher(settingsManager.getHttpIdleTimeoutMs());
+}
+
+/** Harness settings read at every use from pi's settings as loaded at startup. */
+export function createHarnessSettings(settingsManager: SettingsManager): HarnessSettings {
+	return {
+		get stream() {
+			const provider = settingsManager.getProviderRetrySettings();
+			const idle = settingsManager.getHttpIdleTimeoutMs();
+			return {
+				timeoutMs: provider.timeoutMs ?? (idle === 0 ? 2147483647 : idle),
+				maxRetryDelayMs: provider.maxRetryDelayMs,
+				...(provider.maxRetries === undefined ? {} : { maxRetries: provider.maxRetries }),
+			};
+		},
+		get compaction() {
+			return settingsManager.getCompactionSettings();
+		},
+		get retry() {
+			return settingsManager.getRetrySettings();
+		},
+		get steeringMode() {
+			return settingsManager.getSteeringMode();
+		},
+		get followUpMode() {
+			return settingsManager.getFollowUpMode();
+		},
+	};
+}
+
+/** A registry with the vacation planner and its research subagent's search. No coding tools, no pi prompt. */
+export function createVacationRegistry(): Registry {
+	const registry = createRegistry();
+	registry.install(Vacation);
+	registry.install(Search);
+	return registry;
+}
+
+export interface InitialModel {
+	readonly model?: ModelRef;
+	readonly thinkingLevel?: ModelThinkingLevel;
+	readonly fallbackMessage?: string;
+}
+
+/** The model a new root conversation starts with: an explicit `--provider`/`--model`, or pi's default resolution. */
+export async function findInitialAgentModel(
+	settingsManager: SettingsManager,
+	modelRuntime: ModelRuntime,
+	cli?: { readonly provider?: string; readonly model: string },
+): Promise<InitialModel> {
+	if (cli !== undefined) {
+		const resolved = resolveCliModel({ cliProvider: cli.provider, cliModel: cli.model, modelRuntime });
+		if (resolved.error !== undefined || resolved.model === undefined) {
+			throw new Error(`Could not resolve model: ${resolved.error ?? cli.model}`);
+		}
+		return {
+			model: { provider: resolved.model.provider, modelId: resolved.model.id },
+			...(resolved.thinkingLevel === undefined ? {} : { thinkingLevel: resolved.thinkingLevel }),
+		};
+	}
+	const initial = await findInitialModel({
+		scopedModels: [],
+		isContinuing: false,
+		defaultProvider: settingsManager.getDefaultProvider(),
+		defaultModelId: settingsManager.getDefaultModel(),
+		defaultThinkingLevel: settingsManager.getDefaultThinkingLevel(),
+		modelRuntime,
+	});
+	return {
+		...(initial.model === undefined
+			? {}
+			: {
+					model: { provider: initial.model.provider, modelId: initial.model.id },
+					thinkingLevel: initial.thinkingLevel,
+				}),
+		...(initial.fallbackMessage === undefined ? {} : { fallbackMessage: initial.fallbackMessage }),
+	};
+}
diff --git a/packages/coding-agent/src/experimental/vacation/main.ts b/packages/coding-agent/src/experimental/vacation/main.ts
new file mode 100644
index 000000000..d3d843d5f
--- /dev/null
+++ b/packages/coding-agent/src/experimental/vacation/main.ts
@@ -0,0 +1,20 @@
+#!/usr/bin/env node
+
+import { type OpenDurableOptions, openDurable } from "./runtime.ts";
+import { runDurableTui } from "./tui.ts";
+
+function parseArgs(argv: readonly string[]): OpenDurableOptions {
+	let continueSession = false;
+	for (const arg of argv) {
+		if (arg === "--continue" || arg === "-c") continueSession = true;
+		else throw new Error(`Unknown argument: ${arg}`);
+	}
+	return { continueSession };
+}
+
+const durable = await openDurable(parseArgs(process.argv.slice(2)));
+try {
+	await runDurableTui(durable.view, durable.controller, durable.settings);
+} finally {
+	await durable.close();
+}
diff --git a/packages/coding-agent/src/experimental/vacation/runtime.ts b/packages/coding-agent/src/experimental/vacation/runtime.ts
new file mode 100644
index 000000000..0c9b8d268
--- /dev/null
+++ b/packages/coding-agent/src/experimental/vacation/runtime.ts
@@ -0,0 +1,363 @@
+import type { AttachedReplicatedState } from "@earendil-works/chord";
+import { BACKGROUND_CONTEXT } from "@earendil-works/chord/context";
+import { clampThinkingLevel, getSupportedThinkingLevels, type ModelThinkingLevel } from "@earendil-works/pi-ai";
+import {
+	type AgentState,
+	type Conversation,
+	type ConversationId,
+	type ConversationView,
+	type Cursor,
+	type EntryRecord,
+	Harness,
+	type ModelRef,
+	ROOT_CONVERSATION_ID,
+	type Submission,
+	type TaskGraph,
+} from "@earendil-works/pi-durable";
+import { openNodeSqliteStorage } from "@earendil-works/pi-durable/storage/sqlite/node";
+import { ModelRuntime } from "../../core/model-runtime.ts";
+import { SettingsManager } from "../../core/settings-manager.ts";
+import {
+	configureHarnessHttp,
+	createHarnessSettings,
+	createVacationRegistry,
+	findInitialAgentModel,
+} from "./harness-setup.ts";
+import { selectSession } from "./sessions.ts";
+import { Vacation } from "./vacation.ts";
+
+const context = BACKGROUND_CONTEXT;
+
+export interface ModelSummary extends ModelRef {
+	readonly name: string;
+	readonly contextWindow: number;
+}
+
+export interface Notice {
+	readonly id: number;
+	readonly level: "info" | "warning" | "error";
+	readonly message: string;
+}
+
+/** A conversation the user can switch to: the main one, or a subagent's. */
+export interface ConversationSummary {
+	readonly id: ConversationId;
+	readonly label: string;
+	/** The first user message, for a subagent its task. */
+	readonly title?: string;
+}
+
+/** Everything the TUI renders. Plain values; no Harness objects cross this boundary. */
+export interface DurableView {
+	readonly session: { readonly id: string; readonly directory: string; readonly cwd: string };
+	/** The conversation shown and talked to. */
+	readonly conversation: ConversationView;
+	readonly conversations: readonly ConversationSummary[];
+	readonly models: readonly ModelSummary[];
+	readonly notices: readonly Notice[];
+	/** The live task graph while the task panel is open. */
+	readonly tasks?: TaskGraph;
+}
+
+export interface DurableViewSource {
+	current(): DurableView;
+	subscribe(listener: () => void): () => void;
+}
+
+/** What the TUI may ask for. */
+export interface DurableController {
+	/** Prompt when idle; otherwise steer or queue a follow-up. */
+	submit(text: string, whenBusy: "steer" | "followUp"): Promise<void>;
+	compact(instructions: string | undefined): Promise<void>;
+	abort(): Promise<void>;
+	cycleThinking(): Promise<void>;
+	setModel(model: ModelRef): Promise<void>;
+	toggleTasks(): Promise<void>;
+	/** Show and talk to another conversation. */
+	switchConversation(id: ConversationId): Promise<void>;
+}
+
+export interface OpenDurableOptions {
+	readonly cwd?: string;
+	readonly continueSession?: boolean;
+}
+
+export interface OpenDurableResult {
+	readonly view: DurableViewSource;
+	readonly controller: DurableController;
+	/** pi's settings, for the TUI's theme and terminal capabilities. */
+	readonly settings: SettingsManager;
+	close(): Promise<void>;
+}
+
+/** The agent document of a view; absent while the conversation has none. */
+export function agentOf(view: ConversationView): AgentState {
+	return (view.docs["pi.agent"] ?? {}) as AgentState;
+}
+
+/** A subagent's task: the oldest user message of its conversation. The main conversation needs no title. */
+async function firstInput(harness: Harness, id: ConversationId): Promise<{ title?: string }> {
+	if (id === ROOT_CONVERSATION_ID) return {};
+	const conversation = (await harness.conversation(id, context))!;
+	let first: EntryRecord | undefined;
+	let cursor: Cursor | undefined;
+	do {
+		const page = await conversation.entries({}, 256, cursor, context);
+		first = page.items.findLast((entry) => entry.kind === "pi.user") ?? first;
+		cursor = page.next;
+	} while (cursor !== undefined);
+	return titleOf(first);
+}
+
+/** The text of a user entry, as a one-line title. */
+function titleOf(entry: EntryRecord | undefined): { title?: string } {
+	const message = entry?.model?.[0];
+	if (message?.role !== "user") return {};
+	const text =
+		typeof message.content === "string"
+			? message.content
+			: message.content.flatMap((block) => (block.type === "text" ? [block.text] : [])).join(" ");
+	return { title: text.replace(/\s+/g, " ").trim() };
+}
+
+export async function openDurable(options: OpenDurableOptions = {}): Promise<OpenDurableResult> {
+	const location = await selectSession(options.cwd ?? process.cwd(), options.continueSession ?? false);
+	let harness: Harness | undefined;
+	try {
+		const modelRuntime = await ModelRuntime.create();
+		const settingsManager = SettingsManager.create(location.cwd);
+		configureHarnessHttp(settingsManager);
+		const settings = createHarnessSettings(settingsManager);
+		const registry = createVacationRegistry();
+
+		const pendingReports: unknown[] = [];
+		let report: (error: unknown) => void = (error) => pendingReports.push(error);
+		harness = await Harness.open(
+			await openNodeSqliteStorage(location.database),
+			{
+				models: modelRuntime,
+				registry,
+				settings,
+				onReport: (error) => report(error),
+			},
+			context,
+		);
+		const initial = location.created ? await findInitialAgentModel(settingsManager, modelRuntime) : undefined;
+		const root = await harness.root(context, {
+			agent: {
+				// Only the vacation planner; the research subagent selects search itself.
+				extensions: [Vacation],
+				...(initial?.model === undefined ? {} : { model: initial.model }),
+				...(initial?.thinkingLevel === undefined ? {} : { thinkingLevel: initial.thinkingLevel }),
+			},
+		});
+		const label = (id: ConversationId): string => (id === root.id ? "main" : `subagent ${id}`);
+		const opened = harness;
+		const summaries: ConversationSummary[] = [];
+		let cursor: Cursor | undefined;
+		do {
+			const page = await opened.commit((tx) => tx.scanConversations({}, 256, cursor), context);
+			for (const { id } of page.items) summaries.push({ id, label: label(id), ...(await firstInput(opened, id)) });
+			cursor = page.next;
+		} while (cursor !== undefined);
+		let current: Conversation = root;
+		let conversation: AttachedReplicatedState<ConversationView> = await root.viewState(context);
+		const models = (): ModelSummary[] =>
+			modelRuntime.getAvailableSnapshot().map((model) => ({
+				provider: model.provider,
+				modelId: model.id,
+				name: model.name,
+				contextWindow: model.contextWindow,
+			}));
+
+		let state: DurableView = {
+			session: { id: location.id, directory: location.directory, cwd: location.cwd },
+			conversation: conversation.value,
+			conversations: summaries,
+			models: models(),
+			notices: [],
+		};
+		const listeners = new Set<() => void>();
+		let notifying = false;
+		// Commit listeners and Chord frames call this on the Session line; rendering runs afterwards, once per burst.
+		const update = (patch: Partial<DurableView>): void => {
+			state = { ...state, ...patch };
+			if (notifying) return;
+			notifying = true;
+			setImmediate(() => {
+				notifying = false;
+				for (const listener of listeners) listener();
+			});
+		};
+		let nextNotice = 1;
+		const notice = (level: Notice["level"], message: string): void => {
+			update({ notices: [...state.notices, { id: nextNotice++, level, message }].slice(-20) });
+		};
+		const fail = (error: unknown): void => notice("error", error instanceof Error ? error.message : String(error));
+		report = (error) => notice("warning", error instanceof Error ? error.message : String(error));
+		for (const error of pendingReports) report(error);
+		let unsubscribe = conversation.subscribe((value) => update({ conversation: value }));
+		// Subagents appear as their conversations are created. A commit listener only records; it calls no Session API.
+		const unsubscribeCommits = harness.subscribeCommits((publication) => {
+			let conversations = state.conversations;
+			for (const change of publication.changes) {
+				if (change.type === "conversation") {
+					conversations = [...conversations, { id: change.value.id, label: label(change.value.id) }];
+				} else if (change.type === "entry" && change.value.kind === "pi.user") {
+					const id = change.value.conversationId;
+					conversations = conversations.map((summary) =>
+						summary.id === id && summary.title === undefined ? { ...summary, ...titleOf(change.value) } : summary,
+					);
+				}
+			}
+			if (conversations !== state.conversations) update({ conversations });
+		});
+
+		let tasks: AttachedReplicatedState<TaskGraph> | undefined;
+		let unsubscribeTasks = (): void => {};
+		const closeTasks = (): void => {
+			unsubscribeTasks();
+			tasks?.dispose();
+			tasks = undefined;
+		};
+
+		let queue = Promise.resolve();
+		// One at a time, so toggles, switches, and key presses apply in order.
+		const command = (operation: () => Promise<void>): Promise<void> => {
+			queue = queue.then(operation).catch(fail);
+			return queue;
+		};
+		const watchAnswer = (submission: Submission): void => {
+			void submission.wait(context).then((settled) => {
+				if (settled.status === "unanswered" && settled.reason !== "aborted") {
+					notice(
+						"error",
+						`No answer: ${settled.reason}${settled.detail === undefined ? "" : ` ${JSON.stringify(settled.detail)}`}`,
+					);
+				}
+			}, fail);
+		};
+		const agentModel = () => {
+			const ref = agentOf(state.conversation).model;
+			const model = ref === undefined ? undefined : modelRuntime.getModel(ref.provider, ref.modelId);
+			if (model === undefined)
+				throw new Error(ref === undefined ? "No model selected" : "Current model is unavailable");
+			return model;
+		};
+		const controller: DurableController = {
+			submit: (text, whenBusy) =>
+				command(async () => watchAnswer(await current.submit({ type: "input", content: text, whenBusy }, context))),
+			compact: (instructions) =>
+				command(async () => {
+					const id = await current.compact(instructions, context);
+					// Report the outcome once it is known; the status line shows the compaction meanwhile.
+					void opened.waitForTask(id, context).then(async (receipt) => {
+						const outcome = receipt.state.outcome;
+						if (outcome.status === "completed") {
+							const { entryId, submissionId } = outcome.result;
+							// A summary written while busy is a submission: placed now, queued, or dropped as stale.
+							const status =
+								submissionId === undefined
+									? undefined
+									: (await (await opened.submission(submissionId, context))?.status(context))?.status;
+							notice(
+								"info",
+								entryId !== undefined || status === "done"
+									? "Compacted."
+									: status === "queued"
+										? "Compaction summary queued; it is placed at the next turn boundary."
+										: status === "unanswered"
+											? "Compaction summary dropped: the context changed under it."
+											: "Nothing to compact: the context fits in the recent window that is kept verbatim.",
+							);
+						} else if (outcome.status === "aborted") notice("info", "Compaction aborted.");
+						else
+							notice("error", `Compaction ${outcome.status}: ${outcome.error?.message ?? outcome.reason ?? ""}`);
+					}, fail);
+				}),
+			// Not queued: it waits until the conversation is idle.
+			abort: () => current.abort(context).catch(fail),
+			cycleThinking: () =>
+				command(async () => {
+					const model = agentModel();
+					if (!model.reasoning) throw new Error("Current model does not support thinking");
+					const levels = getSupportedThinkingLevels(model);
+					const level = agentOf(state.conversation).thinkingLevel ?? "off";
+					const next = levels[(levels.indexOf(level) + 1) % levels.length] ?? "off";
+					await current.configure({ thinkingLevel: next }, context);
+				}),
+			setModel: (ref) =>
+				command(async () => {
+					const model = modelRuntime.getModel(ref.provider, ref.modelId);
+					if (model === undefined) throw new Error(`Unknown model: ${ref.provider}/${ref.modelId}`);
+					const thinking: ModelThinkingLevel = agentOf(state.conversation).thinkingLevel ?? "off";
+					await current.configure({ model: ref, thinkingLevel: clampThinkingLevel(model, thinking) }, context);
+				}),
+			toggleTasks: () =>
+				command(async () => {
+					if (tasks !== undefined) {
+						closeTasks();
+						update({ tasks: undefined });
+						return;
+					}
+					const graph = await opened.taskGraph(context);
+					tasks = graph;
+					unsubscribeTasks = graph.subscribe((value) => update({ tasks: value }));
+				}),
+			switchConversation: (id) =>
+				command(async () => {
+					const next = await opened.conversation(id, context);
+					if (next === undefined) throw new Error(`Conversation ${id} does not exist`);
+					const nextState = await next.viewState(context);
+					unsubscribe();
+					conversation.dispose();
+					current = next;
+					conversation = nextState;
+					unsubscribe = nextState.subscribe((value) => update({ conversation: value }));
+				}),
+		};
+
+		const saved = agentOf(state.conversation).model;
+		if (saved === undefined) notice("warning", "No model configured; select one with /model.");
+		else if (modelRuntime.getModel(saved.provider, saved.modelId) === undefined) {
+			notice("warning", `Saved model is unavailable: ${saved.provider}/${saved.modelId}`);
+		}
+		if (initial?.fallbackMessage !== undefined) notice("info", initial.fallbackMessage);
+		// The task panel starts open; /tasks hides it.
+		await controller.toggleTasks();
+		// Recovered work from an interrupted turn continues now.
+		harness.resume();
+
+		let closing: Promise<void> | undefined;
+		return {
+			view: {
+				current: () => state,
+				subscribe: (listener) => {
+					listeners.add(listener);
+					return () => listeners.delete(listener);
+				},
+			},
+			controller,
+			settings: settingsManager,
+			close() {
+				closing ??= (async () => {
+					unsubscribe();
+					unsubscribeCommits();
+					conversation.dispose();
+					closeTasks();
+					try {
+						// Close writes no outcome: a running turn resumes with --continue.
+						await opened.close(context);
+					} finally {
+						await location.release();
+					}
+				})();
+				return closing;
+			},
+		};
+	} catch (error) {
+		await harness?.close(context).catch(() => {});
+		await location.release().catch(() => {});
+		throw error;
+	}
+}
diff --git a/packages/coding-agent/src/experimental/vacation/sessions.ts b/packages/coding-agent/src/experimental/vacation/sessions.ts
new file mode 100644
index 000000000..f5dabe2a9
--- /dev/null
+++ b/packages/coding-agent/src/experimental/vacation/sessions.ts
@@ -0,0 +1,56 @@
+import { createHash, randomUUID } from "node:crypto";
+import { mkdir, readdir, realpath } from "node:fs/promises";
+import { basename, join, resolve } from "node:path";
+import lockfile from "proper-lockfile";
+import { getAgentDir } from "../../config.ts";
+
+/** One session directory holding `session.sqlite`, locked by this process. */
+export interface SessionLocation {
+	id: string;
+	directory: string;
+	database: string;
+	cwd: string;
+	created: boolean;
+	release(): Promise<void>;
+}
+
+/** A new session for `cwd`, or its newest one with `continueSession`. */
+export async function selectSession(cwdInput: string, continueSession: boolean): Promise<SessionLocation> {
+	const cwd = await realpath(resolve(cwdInput));
+	const root = join(
+		getAgentDir(),
+		"experimental",
+		"vacation-sessions",
+		createHash("sha256").update(cwd).digest("hex").slice(0, 24),
+	);
+	await mkdir(root, { recursive: true });
+
+	let directory: string;
+	let created = false;
+	if (continueSession) {
+		const entries = await readdir(root, { withFileTypes: true });
+		const newest = entries
+			.filter((entry) => entry.isDirectory() && /^\d{13}-[0-9a-f-]{36}$/u.test(entry.name))
+			.map((entry) => entry.name)
+			.sort()
+			.at(-1);
+		if (!newest) throw new Error(`No vacation session exists for ${cwd}`);
+		directory = join(root, newest);
+	} else {
+		directory = join(root, `${String(Date.now()).padStart(13, "0")}-${randomUUID()}`);
+		await mkdir(directory);
+		created = true;
+	}
+
+	let release: () => Promise<void>;
+	try {
+		// A lock left by a crashed process goes stale after 10 s; wait that long before giving up.
+		release = await lockfile.lock(directory, {
+			realpath: false,
+			retries: { retries: 12, minTimeout: 1000, maxTimeout: 1000 },
+		});
+	} catch (error) {
+		throw new Error(`Session is already open in another process: ${directory}`, { cause: error });
+	}
+	return { id: basename(directory), directory, database: join(directory, "session.sqlite"), cwd, created, release };
+}
diff --git a/packages/coding-agent/src/experimental/vacation/tui.ts b/packages/coding-agent/src/experimental/vacation/tui.ts
new file mode 100644
index 000000000..397b276cb
--- /dev/null
+++ b/packages/coding-agent/src/experimental/vacation/tui.ts
@@ -0,0 +1,655 @@
+import type { AssistantMessage, ToolResultMessage, Usage, UserMessage } from "@earendil-works/pi-ai";
+import type {
+	ConversationId,
+	EntryRecord,
+	InboxState,
+	LiveState,
+	TaskGraph,
+	TaskGraphNode,
+	UsageState,
+} from "@earendil-works/pi-durable";
+import {
+	Box,
+	type Component,
+	Container,
+	type Focusable,
+	fuzzyFilter,
+	getKeybindings,
+	Input,
+	Markdown,
+	ProcessTerminal,
+	ScrollView,
+	type SelectItem,
+	SelectList,
+	type SelectListTheme,
+	Spacer,
+	setCapabilityOverrides,
+	setKeybindings,
+	Text,
+	TruncatedText,
+	TuiAltScreen,
+	VStack,
+} from "@earendil-works/pi-tui";
+import { getAgentDir } from "../../config.ts";
+import { KeybindingsManager } from "../../core/keybindings.ts";
+import type { SettingsManager } from "../../core/settings-manager.ts";
+import { createAllToolRenderers } from "../../core/tools/renderers/index.ts";
+import { AssistantMessageComponent } from "../../modes/interactive/components/assistant-message.ts";
+import { CustomEditor } from "../../modes/interactive/components/custom-editor.ts";
+import { DynamicBorder } from "../../modes/interactive/components/dynamic-border.ts";
+import { formatTokens } from "../../modes/interactive/components/footer.ts";
+import { keyText } from "../../modes/interactive/components/keybinding-hints.ts";
+import { type StatusIndicator, WorkingStatusIndicator } from "../../modes/interactive/components/status-indicator.ts";
+import { ToolExecutionComponent, type ToolRenderers } from "../../modes/interactive/components/tool-execution.ts";
+import { UserMessageComponent } from "../../modes/interactive/components/user-message.ts";
+import { getEditorTheme, getMarkdownTheme, initTheme, theme } from "../../modes/interactive/theme/theme.ts";
+import { InteractiveThemeController } from "../../modes/interactive/theme/theme-controller.ts";
+import { agentOf, type DurableController, type DurableView, type DurableViewSource } from "./runtime.ts";
+
+const SELECT_THEME: SelectListTheme = {
+	selectedPrefix: (text) => theme.fg("accent", text),
+	selectedText: (text) => theme.fg("accent", text),
+	description: (text) => theme.fg("muted", text),
+	scrollInfo: (text) => theme.fg("dim", text),
+	noMatch: (text) => theme.fg("warning", text),
+};
+
+/** A filterable list in place of the editor. */
+class ListSelector extends Container implements Focusable {
+	readonly #input = new Input();
+	readonly #listContainer = new Container();
+	readonly #items: SelectItem[];
+	readonly #onSelect: (value: string) => void;
+	readonly #onCancel: () => void;
+	#list: SelectList;
+	#focused = false;
+
+	constructor(title: string, items: SelectItem[], onSelect: (value: string) => void, onCancel: () => void) {
+		super();
+		this.#items = items;
+		this.#onSelect = onSelect;
+		this.#onCancel = onCancel;
+		this.#list = this.#build(items);
+		this.addChild(new DynamicBorder());
+		this.addChild(new Spacer(1));
+		this.addChild(new Text(theme.fg("accent", theme.bold(title)), 1, 0));
+		this.addChild(this.#input);
+		this.addChild(new Spacer(1));
+		this.addChild(this.#listContainer);
+		this.addChild(new DynamicBorder());
+	}
+
+	get focused(): boolean {
+		return this.#focused;
+	}
+	set focused(value: boolean) {
+		this.#focused = value;
+		this.#input.focused = value;
+	}
+
+	handleInput(data: string): void {
+		const keybindings = getKeybindings();
+		const forwarded = ["tui.select.up", "tui.select.down", "tui.select.confirm", "tui.select.cancel"] as const;
+		if (forwarded.some((action) => keybindings.matches(data, action))) {
+			this.#list.handleInput(data);
+			return;
+		}
+		this.#input.handleInput(data);
+		const query = this.#input.getValue();
+		const filtered =
+			query.length === 0 ? this.#items : fuzzyFilter(this.#items, query, (item) => `${item.label} ${item.value}`);
+		this.#list = this.#build(filtered);
+	}
+
+	#build(items: SelectItem[]): SelectList {
+		const list = new SelectList(items, 10, SELECT_THEME);
+		list.onSelect = (item) => this.#onSelect(item.value);
+		list.onCancel = this.#onCancel;
+		this.#listContainer.clear();
+		this.#listContainer.addChild(list);
+		return list;
+	}
+}
+
+/** The summary that replaced earlier context: collapsed to one line until expanded. */
+class CompactionComponent extends Box {
+	readonly #summary: string;
+
+	constructor(summary: string, expanded: boolean) {
+		super(1, 1, (text) => theme.bg("customMessageBg", text));
+		this.#summary = summary;
+		this.setExpanded(expanded);
+	}
+
+	setExpanded(expanded: boolean): void {
+		this.clear();
+		this.addChild(new Text(theme.fg("customMessageLabel", theme.bold("[compaction]")), 0, 0));
+		this.addChild(new Spacer(1));
+		this.addChild(
+			expanded
+				? new Markdown(this.#summary, 0, 0, getMarkdownTheme(), {
+						color: (text: string) => theme.fg("customMessageText", text),
+					})
+				: new Text(
+						theme.fg("customMessageText", "Earlier context summarized (") +
+							theme.fg("dim", keyText("app.tools.expand")) +
+							theme.fg("customMessageText", " to expand)"),
+						0,
+						0,
+					),
+		);
+	}
+}
+
+interface Handlers {
+	submit(text: string): void;
+	followUp(text: string): void;
+	abort(): void;
+	exit(): void;
+	selectModel(): void;
+	cycleThinking(): void;
+}
+
+class DurableTui {
+	static readonly #renderers: Record<string, ToolRenderers> = createAllToolRenderers();
+	readonly #ui: TuiAltScreen;
+	readonly #chat = new Container();
+	readonly #tasks = new Container();
+	readonly #queue = new Container();
+	readonly #notices = new Container();
+	readonly #footer = new Container();
+	readonly #footerStats = new Text("", 1, 0);
+	readonly #footerHints = new Text("", 1, 0);
+	readonly #editorContainer = new Container();
+	readonly #editor: CustomEditor;
+	readonly #cwd: string;
+	/** The newest card per call ID; provider call IDs may repeat across turns. */
+	readonly #tools = new Map<string, ToolExecutionComponent>();
+	/** Every card shown, also older ones whose call ID a later turn reused. */
+	readonly #cards: ToolExecutionComponent[] = [];
+	/** Call IDs whose cards the streaming answer created; its entry takes them over. */
+	readonly #streamingCalls = new Set<string>();
+	readonly #summaries: CompactionComponent[] = [];
+	/** Tool output and summaries shown in full; toggled like pi. */
+	#expanded = false;
+	#renderedEntryIds: number[] = [];
+	#streaming: AssistantMessageComponent | undefined;
+	#indicator: StatusIndicator | undefined;
+	#statusText = "";
+	/** Set when the transcript was rebuilt: the next render repaints the screen and shows the end. */
+	#rebuilt = false;
+	#transcript: ScrollView;
+
+	constructor(cwd: string, handlers: Handlers) {
+		this.#cwd = cwd;
+		this.#ui = new TuiAltScreen(new ProcessTerminal(), false, getAgentDir());
+		const keybindings = KeybindingsManager.create();
+		setKeybindings(keybindings);
+		this.#editor = new CustomEditor(this.#ui, getEditorTheme(), keybindings, {
+			paddingX: 1,
+			embedWorkingStatus: true,
+		});
+		this.#editor.onSubmit = handlers.submit;
+		this.#editor.onEscape = handlers.abort;
+		this.#editor.onCtrlD = handlers.exit;
+		this.#editor.onAction("app.clear", handlers.exit);
+		this.#editor.onAction("app.model.select", handlers.selectModel);
+		this.#editor.onAction("app.thinking.cycle", handlers.cycleThinking);
+		this.#editor.onAction("app.tools.expand", () => {
+			this.#expanded = !this.#expanded;
+			for (const component of [...this.#cards, ...this.#summaries]) component.setExpanded(this.#expanded);
+			this.#ui.requestRender();
+		});
+		this.#editor.onAction("app.message.followUp", () => {
+			const text = this.#editor.getText().trim();
+			if (!text) return;
+			this.#editor.setText("");
+			handlers.followUp(text);
+		});
+
+		this.#editorContainer.addChild(this.#editor);
+		this.#footer.addChild(this.#footerStats);
+		this.#footer.addChild(this.#footerHints);
+		// One empty line between the transcript and everything below it.
+		const content = new Container();
+		content.addChild(this.#chat);
+		content.addChild(new Spacer(1));
+		const transcript = new ScrollView(content, { follow: "end", primary: true, overscroll: "chain" });
+		this.#transcript = transcript;
+		const dock = new VStack([
+			{ component: this.#tasks, shrink: 1, minSize: 0 },
+			{ component: this.#queue, shrink: 1, minSize: 0 },
+			{ component: this.#notices, shrink: 1, minSize: 0 },
+			{ component: this.#editorContainer, shrink: 1, minSize: 3 },
+			{ component: this.#footer, shrink: 1, minSize: 0 },
+		]);
+		for (const component of [
+			this.#chat,
+			this.#tasks,
+			this.#queue,
+			this.#notices,
+			this.#editorContainer,
+			this.#footer,
+		]) {
+			this.#ui.addChild(component);
+		}
+		this.#ui.setLayoutRoot(
+			new VStack([
+				{ component: transcript, basis: 0, grow: 1, shrink: 1, minSize: 1 },
+				{ component: dock, basis: "auto", grow: 0, shrink: 1, minSize: 1 },
+			]),
+		);
+		this.#ui.setFocus(this.#editor);
+	}
+
+	get ui(): TuiAltScreen {
+		return this.#ui;
+	}
+
+	start(): void {
+		this.#ui.start();
+	}
+
+	stop(): void {
+		this.#discardTools();
+		this.#indicator?.dispose();
+		this.#ui.stop();
+	}
+
+	/** Finish every card: a running bash card keeps a timer until it gets a final result. */
+	#discardTools(): void {
+		for (const component of this.#cards) component.updateResult({ content: [], isError: false }, false);
+		this.#cards.length = 0;
+		this.#tools.clear();
+		this.#streamingCalls.clear();
+	}
+
+	mount(component: Component): void {
+		this.#editorContainer.clear();
+		this.#editorContainer.addChild(component);
+		this.#ui.setFocus(component);
+		this.#ui.requestRender();
+	}
+
+	restoreEditor(): void {
+		this.mount(this.#editor);
+	}
+
+	apply(view: DurableView): void {
+		const live = (view.conversation.docs["pi.live"] ?? {}) as LiveState;
+		this.#syncTranscript(view.conversation.entries);
+		const message = live.generation?.message as AssistantMessage | undefined;
+		// A partial without its entry was dropped, for example by a retry: render the transcript again.
+		if (message === undefined && this.#streaming !== undefined) this.#rebuild(view.conversation.entries);
+		if (message !== undefined) this.#syncStreaming(message);
+		for (const slot of live.tools ?? []) {
+			if (slot.status === "pending") continue;
+			const component = this.#tool(slot.name, slot.callId);
+			component.setArgsComplete();
+			if (slot.status !== "running") continue;
+			component.markExecutionStarted();
+			const child = (slot.details as { conversationId?: number } | undefined)?.conversationId;
+			if (slot.output === undefined && child !== undefined) {
+				const text = `Subagent ${child} is working. /agents switches to it.`;
+				component.updateResult({ content: [{ type: "text", text }], details: slot.details, isError: false }, true);
+			} else if (slot.output !== undefined) {
+				component.updateResult(
+					{ content: [{ type: "text", text: slot.output }], details: slot.details, isError: false },
+					true,
+				);
+			}
+		}
+		this.#syncTasks(view.tasks);
+		this.#syncQueue((view.conversation.docs["pi.inbox"] ?? { items: [] }) as InboxState);
+		this.#syncNotices(view);
+		this.#editor.borderColor = theme.getThinkingBorderColor(agentOf(view.conversation).thinkingLevel ?? "off");
+		this.#syncStatus(live);
+		this.#syncFooter(view);
+		if (this.#rebuilt) this.#transcript.scrollToEnd();
+		this.#ui.requestRender(this.#rebuilt);
+		this.#rebuilt = false;
+	}
+
+	#syncTasks(graph: TaskGraph | undefined): void {
+		this.#tasks.clear();
+		if (graph === undefined) return;
+		const nodes = Object.values(graph.tasks);
+		const lines: string[] = [theme.fg("accent", `Tasks (${nodes.length} live, /tasks to hide)`)];
+		// A conversation-owned task sits under the task that owns its conversation, when that task is live.
+		const owned = new Set(nodes.flatMap((node) => node.conversations));
+		const children = (node: TaskGraphNode) =>
+			nodes.filter(
+				(candidate) =>
+					candidate.owner === node.id ||
+					(candidate.owner === undefined && node.conversations.includes(candidate.conversationId)),
+			);
+		const visit = (node: TaskGraphNode, depth: number): void => {
+			lines.push(`${"  ".repeat(depth + 1)}${describeTask(node)}`);
+			for (const child of children(node)) visit(child, depth + 1);
+		};
+		for (const node of nodes) {
+			if (node.owner === undefined && !owned.has(node.conversationId)) visit(node, 0);
+		}
+		for (const line of lines) this.#tasks.addChild(new TruncatedText(theme.fg("muted", line), 1, 0));
+	}
+
+	#syncQueue(inbox: InboxState): void {
+		this.#queue.clear();
+		for (const item of inbox.items) {
+			const text =
+				item.mode === "write" ? `<${String(item.entry.kind)}>` : userText(item.content as UserMessage["content"]);
+			this.#queue.addChild(new TruncatedText(theme.fg("muted", `[${item.mode}] ${text}`), 1, 0));
+		}
+	}
+
+	#syncNotices(view: DurableView): void {
+		this.#notices.clear();
+		for (const item of view.notices.slice(-4)) {
+			const color = item.level === "error" ? "error" : item.level === "warning" ? "warning" : "muted";
+			this.#notices.addChild(new TruncatedText(theme.fg(color, item.message), 1, 0));
+		}
+	}
+
+	#syncStatus(live: LiveState): void {
+		const generation = live.generation;
+		const compaction = live.compactions?.[0];
+		const runningTool = live.tools?.find((slot) => slot.status === "running");
+		let text = "";
+		if (generation?.retry !== undefined) {
+			text = `Retrying (attempt ${generation.attempt + 1}): ${generation.retry.error}`;
+		} else if (generation?.deferred !== undefined) text = "Waiting for deferred response...";
+		else if (compaction !== undefined) {
+			text = compaction.retry
+				? `Retrying ${compaction.reason} compaction (attempt ${compaction.attempt + 1})...`
+				: `Compacting (${compaction.reason})...`;
+		} else if (runningTool !== undefined) text = `Running ${runningTool.name}... (esc to abort)`;
+		else if (live.run !== undefined) text = "Working... (esc to abort)";
+		if (text === this.#statusText) return;
+		this.#statusText = text;
+		this.#indicator?.dispose();
+		this.#indicator = text
+			? new WorkingStatusIndicator(this.#ui, text, undefined, (part) => this.#editor.borderColor(part))
+			: undefined;
+		this.#editor.setWorkingStatusIndicator(this.#indicator);
+	}
+
+	#syncFooter(view: DurableView): void {
+		const agent = agentOf(view.conversation);
+		const usage = totalUsage((view.conversation.docs["pi.usage"] ?? { models: {}, tools: {} }) as UsageState);
+		const stats: string[] = [];
+		if (usage.input) stats.push(`↑${formatTokens(usage.input)}`);
+		if (usage.output) stats.push(`↓${formatTokens(usage.output)}`);
+		if (usage.cacheRead) stats.push(`R${formatTokens(usage.cacheRead)}`);
+		if (usage.cacheWrite) stats.push(`W${formatTokens(usage.cacheWrite)}`);
+		stats.push(`$${usage.cost.total.toFixed(3)}`);
+		const contextWindow =
+			view.models.find((model) => model.provider === agent.model?.provider && model.modelId === agent.model.modelId)
+				?.contextWindow ?? 0;
+		if (contextWindow > 0) {
+			const tokens = contextTokens(view.conversation.entries);
+			const percent = tokens === undefined ? undefined : (tokens / contextWindow) * 100;
+			const text = `${percent === undefined ? "?" : percent.toFixed(1)}%/${formatTokens(contextWindow)}`;
+			stats.push(percent !== undefined && percent > 90 ? theme.fg("error", text) : text);
+		}
+		this.#footerStats.setText(theme.fg("dim", `${stats.join(" ")}  ${view.session.cwd}`));
+		const model = agent.model === undefined ? "no model" : `${agent.model.provider}/${agent.model.modelId}`;
+		const shown = view.conversations.find((candidate) => candidate.id === view.conversation.conversation.id);
+		const label = shown?.label ?? `conversation ${view.conversation.conversation.id}`;
+		this.#footerHints.setText(
+			`${theme.fg(label === "main" ? "dim" : "accent", label)}${theme.fg(
+				"dim",
+				` · ${model} · thinking:${agent.thinkingLevel ?? "off"} (${keyText("app.thinking.cycle")}) · ${keyText("app.model.select")} or /model · /agents · /compact · /tasks · ${keyText("app.message.followUp")} follow-up · ${keyText("app.clear")} exit`,
+			)}`,
+		);
+	}
+
+	#syncTranscript(entries: readonly EntryRecord[]): void {
+		// Compaction and resets replace the head of the active transcript.
+		if (this.#renderedEntryIds.some((id, index) => entries[index]?.id !== id)) this.#rebuild(entries);
+		for (const entry of entries.slice(this.#renderedEntryIds.length)) {
+			this.#addEntry(entry);
+			this.#renderedEntryIds.push(entry.id);
+		}
+	}
+
+	#rebuild(entries: readonly EntryRecord[]): void {
+		this.#chat.clear();
+		this.#discardTools();
+		this.#summaries.length = 0;
+		this.#rebuilt = true;
+		this.#renderedEntryIds = [];
+		this.#streaming = undefined;
+		for (const entry of entries) {
+			this.#addEntry(entry);
+			this.#renderedEntryIds.push(entry.id);
+		}
+	}
+
+	#addEntry(entry: EntryRecord): void {
+		const message = entry.model?.[0];
+		if (entry.kind === "pi.user" && message?.role === "user") {
+			this.#chat.addChild(new Spacer(1));
+			this.#chat.addChild(new UserMessageComponent(userText(message.content)));
+		} else if (entry.kind === "pi.assistant" && message?.role === "assistant") {
+			const component = this.#streaming ?? new AssistantMessageComponent();
+			if (this.#streaming === undefined) this.#chat.addChild(component);
+			this.#streaming = undefined;
+			component.updateContent(message, false);
+			// Only a tool-calling answer runs its calls; an aborted, failed, or truncated one never does.
+			const ran = message.stopReason === "toolUse";
+			for (const content of message.content) {
+				if (content.type !== "toolCall") continue;
+				const streamed = this.#streamingCalls.has(content.id);
+				// Only cards the stream already showed are kept for calls that never run.
+				if (!ran && !streamed) continue;
+				const card = this.#tool(content.name, content.id, content.arguments, !streamed);
+				card.setArgsComplete();
+				if (!ran) {
+					const text = "Not run: the answer was interrupted.";
+					card.updateResult({ content: [{ type: "text", text }], isError: true }, false);
+				}
+			}
+			this.#streamingCalls.clear();
+		} else if (entry.kind === "pi.tool-result" && message?.role === "toolResult") {
+			const result = message as ToolResultMessage;
+			this.#tool(result.toolName, result.toolCallId).updateResult(result);
+		} else if (entry.kind === "pi.compaction") {
+			const summary = new CompactionComponent(
+				message?.role === "user" ? userText(message.content) : "",
+				this.#expanded,
+			);
+			this.#summaries.push(summary);
+			this.#chat.addChild(new Spacer(1));
+			this.#chat.addChild(summary);
+		} else if (entry.kind === "pi.reset") this.#addText("[new context]");
+	}
+
+	#syncStreaming(message: AssistantMessage): void {
+		if (this.#streaming === undefined) {
+			this.#streaming = new AssistantMessageComponent();
+			this.#chat.addChild(this.#streaming);
+		}
+		this.#streaming.updateContent(message, true);
+		for (const content of message.content) {
+			if (content.type !== "toolCall") continue;
+			this.#tool(content.name, content.id, content.arguments, !this.#streamingCalls.has(content.id));
+			this.#streamingCalls.add(content.id);
+		}
+	}
+
+	#addText(text: string): void {
+		this.#chat.addChild(new Spacer(1));
+		this.#chat.addChild(new Text(theme.fg("muted", text), 1, 0));
+	}
+
+	/** The card of a call; `fresh` starts a new one for a call ID an earlier turn used. */
+	#tool(name: string, callId: string, args?: unknown, fresh = false): ToolExecutionComponent {
+		const existing = fresh ? undefined : this.#tools.get(callId);
+		if (existing !== undefined) {
+			if (args !== undefined) existing.updateArgs(args);
+			return existing;
+		}
+		const component = new ToolExecutionComponent(
+			name,
+			callId,
+			args ?? {},
+			{},
+			DurableTui.#renderers[name],
+			this.#ui,
+			this.#cwd,
+		);
+		component.setExpanded(this.#expanded);
+		this.#chat.addChild(component);
+		this.#cards.push(component);
+		this.#tools.set(callId, component);
+		return component;
+	}
+}
+
+function describeTask(node: TaskGraphNode): string {
+	const state = node.state;
+	const status =
+		state.status === "waiting"
+			? `waiting on ${state.on.join(", ")}`
+			: state.status === "completing"
+				? `completing (${state.outcome})`
+				: `${state.status} ${state.phase}`;
+	const flags = [node.background ? "background" : "", node.abortRequested ? "aborting" : ""].filter(Boolean);
+	const owned = node.conversations.length > 0 ? ` owns conversation ${node.conversations.join(", ")}` : "";
+	return `${node.kind} #${node.id}: ${status}${flags.length > 0 ? ` [${flags.join(", ")}]` : ""}${owned}`;
+}
+
+function userText(content: UserMessage["content"]): string {
+	if (typeof content === "string") return content;
+	return content
+		.filter((block) => block.type === "text")
+		.map((block) => block.text)
+		.join("");
+}
+
+function totalUsage(state: UsageState): Usage {
+	const total: Usage = {
+		input: 0,
+		output: 0,
+		cacheRead: 0,
+		cacheWrite: 0,
+		totalTokens: 0,
+		cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
+	};
+	for (const usage of [...Object.values(state.models), ...Object.values(state.tools)]) {
+		total.input += usage.input;
+		total.output += usage.output;
+		total.cacheRead += usage.cacheRead;
+		total.cacheWrite += usage.cacheWrite;
+		total.cost.total += usage.cost.total;
+	}
+	return total;
+}
+
+/** Context size from the newest successful answer after the newest compaction; unknown before one. */
+function contextTokens(entries: readonly EntryRecord[]): number | undefined {
+	// Kept entries follow the summary in the view but are older than it; only later answers measure the new context.
+	const compacted = Math.max(0, ...entries.filter((entry) => entry.kind === "pi.compaction").map((entry) => entry.id));
+	for (const entry of [...entries].reverse()) {
+		const message = entry.model?.[0];
+		if (entry.id < compacted || entry.kind !== "pi.assistant" || message?.role !== "assistant") continue;
+		if (message.stopReason === "aborted" || message.stopReason === "error") continue;
+		const usage = message.usage;
+		return usage.totalTokens || usage.input + usage.output + usage.cacheRead + usage.cacheWrite;
+	}
+	return undefined;
+}
+
+export async function runDurableTui(
+	source: DurableViewSource,
+	controller: DurableController,
+	settings: SettingsManager,
+): Promise<void> {
+	setCapabilityOverrides(settings.getTerminalCapabilityOverrides());
+	// The system theme until the controller resolves the user's theme against the terminal's colors.
+	initTheme();
+	let exit = (): void => {};
+	const exited = new Promise<void>((resolve) => {
+		exit = resolve;
+	});
+	let view!: DurableTui;
+
+	const selectModel = (): void => {
+		const snapshot = source.current();
+		const current = agentOf(snapshot.conversation).model;
+		const isCurrent = (model: { provider: string; modelId: string }) =>
+			model.provider === current?.provider && model.modelId === current.modelId;
+		const items: SelectItem[] = [...snapshot.models]
+			.sort((left, right) => Number(isCurrent(right)) - Number(isCurrent(left)))
+			.map((model) => ({
+				value: `${model.provider}/${model.modelId}`,
+				label: model.modelId,
+				description: model.provider,
+			}));
+		const selector = new ListSelector(
+			"Select model:",
+			items,
+			(value) => {
+				view.restoreEditor();
+				const separator = value.indexOf("/");
+				void controller.setModel({ provider: value.slice(0, separator), modelId: value.slice(separator + 1) });
+			},
+			() => view.restoreEditor(),
+		);
+		view.mount(selector);
+	};
+
+	const selectConversation = (): void => {
+		const snapshot = source.current();
+		const items: SelectItem[] = [...snapshot.conversations].reverse().map((candidate) => ({
+			value: String(candidate.id),
+			label: candidate.label,
+			description: `${candidate.id === snapshot.conversation.conversation.id ? "(shown) " : ""}${candidate.title ?? ""}`,
+		}));
+		const selector = new ListSelector(
+			"Switch to:",
+			items,
+			(value) => {
+				view.restoreEditor();
+				void controller.switchConversation(Number(value) as ConversationId);
+			},
+			() => view.restoreEditor(),
+		);
+		view.mount(selector);
+	};
+
+	view = new DurableTui(source.current().session.cwd, {
+		submit: (text) => {
+			const trimmed = text.trim();
+			if (!trimmed) return;
+			if (trimmed === "/model") return selectModel();
+			if (trimmed === "/tasks") return void controller.toggleTasks();
+			if (trimmed === "/agents") return selectConversation();
+			if (trimmed === "/compact" || trimmed.startsWith("/compact ")) {
+				const instructions = trimmed.slice("/compact".length).trim();
+				return void controller.compact(instructions || undefined);
+			}
+			void controller.submit(trimmed, "steer");
+		},
+		followUp: (text) => void controller.submit(text, "followUp"),
+		abort: () => void controller.abort(),
+		exit,
+		selectModel,
+		cycleThinking: () => void controller.cycleThinking(),
+	});
+
+	// pi's theme handling: the theme setting (also light/dark pairs) resolved against the terminal's reported colors.
+	const themes = new InteractiveThemeController(view.ui, {
+		getSettingsManager: () => settings,
+		showError: (message) => console.error(message),
+		onChanged: () => view.ui.requestRender(),
+	});
+	const unsubscribe = source.subscribe(() => view.apply(source.current()));
+	view.start();
+	themes.applyFromSettings();
+	view.apply(source.current());
+	await exited;
+	unsubscribe();
+	themes.dispose();
+	view.stop();
+}
diff --git a/packages/coding-agent/src/experimental/vacation/vacation.ts b/packages/coding-agent/src/experimental/vacation/vacation.ts
new file mode 100644
index 000000000..d6fc87513
--- /dev/null
+++ b/packages/coding-agent/src/experimental/vacation/vacation.ts
@@ -0,0 +1,142 @@
+import { setTimeout as sleep } from "node:timers/promises";
+import { Type } from "@earendil-works/pi-ai";
+import {
+	AssistantEntry,
+	type ConversationId,
+	configure,
+	defineExtension,
+	defineTask,
+	defineTool,
+	section,
+} from "@earendil-works/pi-durable";
+
+// ─── search: slow, fake, and safe to rerun ──────────────────────────────────
+
+/** Canned results; each topic takes a different time, so a crash can land between them. */
+const SEARCHES = {
+	weather: {
+		seconds: 6,
+		results: ["Saturday: 24°C and sunny", "Sunday: 21°C, a short shower around 3 pm"],
+	},
+	museums: {
+		seconds: 10,
+		results: [
+			"Kunsthistorisches Museum: open 10-18, book a time slot",
+			"Belvedere: Klimt's The Kiss, quietest before 11",
+			"Albertina: Monet to Picasso, open until 21 on Friday",
+		],
+	},
+	trains: {
+		seconds: 30,
+		results: ["Railjet from Salzburg: 2h 22m, every 30 min", "Nightjet from Munich: arrives 06:20"],
+	},
+} as const;
+
+const search = defineTool({
+	name: "search",
+	description:
+		"Search travel information about a city. Topics: weather, museums, trains. Slow; call several in parallel.",
+	parameters: Type.Object({
+		topic: Type.Union([Type.Literal("weather"), Type.Literal("museums"), Type.Literal("trains")]),
+		city: Type.String(),
+	}),
+	// Only reads, so a call cut off by a crash simply runs again.
+	replay: "safe",
+	execute: async (args, api, context) => {
+		const found = SEARCHES[args.topic];
+		const steps = Math.ceil(found.seconds / 2);
+		for (let step = 1; step <= steps; step++) {
+			api.output(`searching ${args.topic} in ${args.city}: source ${step}/${steps}\n`);
+			await sleep(2000, undefined, { signal: context.abortSignal });
+		}
+		for (const result of found.results) api.output(`- ${result}\n`);
+		return {};
+	},
+});
+
+/** What the research subagent gets: only `search`. */
+export const Search = defineExtension({ name: "vacation-search", tools: [search] });
+
+// ─── research: a background subagent that reports back ──────────────────────
+
+type ResearchState = { phase: "deliver" } | { phase: "report"; report: string };
+
+/** Delivers the task to its subagent and posts the report to the main conversation as a new message. */
+const Research = defineTask<{ task: string }, ResearchState, null>({
+	name: "vacation.research",
+	version: 1,
+	initial: () => ({ phase: "deliver" }),
+	phases: {
+		deliver: async (task, runtime, context) => {
+			// The subagent's conversation is owned by this task. No Session call may run inside a commit.
+			let owned: ConversationId | undefined;
+			await runtime.commit(async (tx) => {
+				owned = (await tx.scanConversations({ ownerTaskId: task.id }, 1)).items[0]?.id;
+				return undefined;
+			}, context);
+			const child = await runtime.conversation(owned!, context);
+			// A rerun after a crash gets the same submission back.
+			const request = { type: "input", content: task.input.task, requestId: `research:${task.id}` } as const;
+			const settled = await (await child!.submit(request, context)).wait(context);
+			await runtime.commit(async (tx) => {
+				let report = `[research report] The research failed: ${settled.status === "unanswered" ? settled.reason : "?"}`;
+				if (settled.status === "done" && settled.type === "input") {
+					const message = (await tx.entry(AssistantEntry, settled.answer))?.model?.[0];
+					const text =
+						message?.role === "assistant"
+							? message.content.flatMap((part) => (part.type === "text" ? [part.text] : [])).join("")
+							: "";
+					report = `[research report] ${text}`;
+				}
+				return { status: "running", checkpoint: { phase: "report", report } };
+			}, context);
+		},
+		report: async (task, runtime, context) => {
+			const main = await runtime.conversation(runtime.conversationId, context);
+			const report = { type: "input", content: task.state.checkpoint.report, whenBusy: "followUp" } as const;
+			await main!.submit({ ...report, requestId: `research-report:${task.id}` }, context);
+			await runtime.commit(() => ({ status: "terminal", outcome: { status: "completed", result: null } }), context);
+		},
+	},
+	abort: (_task, runtime, context) =>
+		runtime.commit(() => ({ status: "terminal", outcome: { status: "aborted" } }), context),
+});
+
+const research = defineTool({
+	name: "research",
+	description:
+		"Start a research subagent in the background. It searches while you keep talking with the user; its report arrives later as a message starting with [research report].",
+	parameters: Type.Object({ task: Type.String({ description: "What to research, with the city and dates" }) }),
+	execute: async (args, api, context) => {
+		await api.commit(async (tx) => {
+			// Background: the main conversation stays free while the research runs.
+			const owner = await tx.createTask(
+				Research,
+				{ task: args.task },
+				{ ownership: { kind: "conversation" }, background: true },
+			);
+			const child = await tx.createConversation({ ownership: { kind: "task", taskId: owner } });
+			await configure(tx, child.id, {
+				extensions: [Search],
+				instructions:
+					"You are a research subagent for a vacation planner. Search weather, museums, and trains in parallel, in one step, then report the findings in a few short bullet points.",
+			});
+		}, context);
+		return { content: [{ type: "text", text: "Research started in the background." }] };
+	},
+});
+
+/** What the main conversation gets: the prompt, `research`, and the task that delivers its report. */
+export const Vacation = defineExtension({
+	name: "vacation",
+	tools: [research],
+	tasks: [Research],
+	sections: [
+		section(
+			"preamble",
+			() =>
+				"You are a friendly vacation planning assistant. Keep answers short. Hand all research to the research tool; while it runs, keep chatting with the user. When a [research report] arrives, turn it into a short plan.",
+			{ tag: false },
+		),
+	],
+});