diff --git a/.lane/memory/apps/host/src/cli.ts/01M4YY5SXJFQK8VXT78X1E0KAE-every-command-but-serve-must.md b/.lane/memory/apps/host/src/cli.ts/01M4YY5SXJFQK8VXT78X1E0KAE-every-command-but-serve-must.md
index e71d8b0e..9b9f24de 100644
--- a/.lane/memory/apps/host/src/cli.ts/01M4YY5SXJFQK8VXT78X1E0KAE-every-command-but-serve-must.md
+++ b/.lane/memory/apps/host/src/cli.ts/01M4YY5SXJFQK8VXT78X1E0KAE-every-command-but-serve-must.md
@@ -4,9 +4,9 @@ anchor: function main
 created: 2026-10-15T04:47:23Z
 norm: '1'
 sig: 7d5d3f63a3bddde4
-body_hash: 2df61fec47c0ebd8
-raw_hash: 0ee7581f4d71df17
-vouched: 2026-10-20T17:05:11Z
+body_hash: 33d554e96630bf6d
+raw_hash: f8aa0b8e89a37828
+vouched: 2026-10-20T17:10:51Z
 lines: 253-482
 ---
 
diff --git a/.lane/memory/apps/host/src/demo.ts/01M5D4PGYZHXCA8WY1C8ZF4NF7-synthetic-people-stay-in-the.md b/.lane/memory/apps/host/src/demo.ts/01M5D4PGYZHXCA8WY1C8ZF4NF7-synthetic-people-stay-in-the.md
new file mode 100644
index 00000000..fb1ec9a6
--- /dev/null
+++ b/.lane/memory/apps/host/src/demo.ts/01M5D4PGYZHXCA8WY1C8ZF4NF7-synthetic-people-stay-in-the.md
@@ -0,0 +1,12 @@
+---
+id: 01M5D4PGYZHXCA8WY1C8ZF4NF7
+anchor: '@file'
+created: 2026-10-20T17:10:44Z
+norm: '1'
+sig: e3b0c44298fc1c14
+body_hash: fead7ca7cb28760f
+raw_hash: 5b36bffc37f91339
+lines: 1-187
+---
+
+Synthetic people stay in the owner's own app frames (people, presence); never publish them to the directory, lobbies or peers
diff --git a/.lane/memory/apps/host/src/gateway.ts/01M4YSPPFYCZDP3MFXKC8YBNFE-lobby-presence-goes-to-the-o.md b/.lane/memory/apps/host/src/gateway.ts/01M4YSPPFYCZDP3MFXKC8YBNFE-lobby-presence-goes-to-the-o.md
index 1a1fc141..96cf98d6 100644
--- a/.lane/memory/apps/host/src/gateway.ts/01M4YSPPFYCZDP3MFXKC8YBNFE-lobby-presence-goes-to-the-o.md
+++ b/.lane/memory/apps/host/src/gateway.ts/01M4YSPPFYCZDP3MFXKC8YBNFE-lobby-presence-goes-to-the-o.md
@@ -4,8 +4,9 @@ anchor: function presenceChanged
 created: 2026-10-15T03:29:13Z
 norm: '1'
 sig: 65636cf5f3dc4666
-body_hash: b14172cdb315f14d
-raw_hash: 708e82787b7742b9
+body_hash: b5bb75b50aa22043
+raw_hash: f87da30c2926f8ef
+vouched: 2026-10-20T17:10:51Z
 lines: 217-222
 ---
 
diff --git a/.lane/memory/apps/host/src/gateway.ts/01M4YT9Z8YJ2ZWZCVB752WDCFF-workers-and-agent-shells-fin.md b/.lane/memory/apps/host/src/gateway.ts/01M4YT9Z8YJ2ZWZCVB752WDCFF-workers-and-agent-shells-fin.md
index 221d0b2a..2539861f 100644
--- a/.lane/memory/apps/host/src/gateway.ts/01M4YT9Z8YJ2ZWZCVB752WDCFF-workers-and-agent-shells-fin.md
+++ b/.lane/memory/apps/host/src/gateway.ts/01M4YT9Z8YJ2ZWZCVB752WDCFF-workers-and-agent-shells-fin.md
@@ -3,10 +3,10 @@ id: 01M4YT9Z8YJ2ZWZCVB752WDCFF
 anchor: function serve
 created: 2026-10-15T03:39:45Z
 norm: '1'
-sig: 9102a6912d6b112c
-body_hash: 7c58dffb06b79595
-raw_hash: 6bf75b65468de74e
-vouched: 2026-10-19T20:58:11Z
+sig: 171797818ef4d836
+body_hash: bbdb9eb136165a77
+raw_hash: db94b1c01ca466d2
+vouched: 2026-10-20T17:10:51Z
 lines: 668-751
 ---
 
diff --git a/.lane/memory/apps/host/src/gateway.ts/01M4ZH1NMBK54TCB970R3AJ1X1-a-loopback-host-must-not-cal.md b/.lane/memory/apps/host/src/gateway.ts/01M4ZH1NMBK54TCB970R3AJ1X1-a-loopback-host-must-not-cal.md
index 504101fc..674bc9aa 100644
--- a/.lane/memory/apps/host/src/gateway.ts/01M4ZH1NMBK54TCB970R3AJ1X1-a-loopback-host-must-not-cal.md
+++ b/.lane/memory/apps/host/src/gateway.ts/01M4ZH1NMBK54TCB970R3AJ1X1-a-loopback-host-must-not-cal.md
@@ -3,10 +3,10 @@ id: 01M4ZH1NMBK54TCB970R3AJ1X1
 anchor: function serve
 created: 2026-10-15T10:17:10Z
 norm: '1'
-sig: 9102a6912d6b112c
-body_hash: 7c58dffb06b79595
-raw_hash: 6bf75b65468de74e
-vouched: 2026-10-19T20:58:11Z
+sig: 171797818ef4d836
+body_hash: bbdb9eb136165a77
+raw_hash: db94b1c01ca466d2
+vouched: 2026-10-20T17:10:51Z
 lines: 830-948
 supersedes: 01M4Z2R1HEVDKEA8VEJ7XRJQ8F
 ---
diff --git a/.lane/memory/apps/host/src/gateway.ts/01M50KBA3ME0Q9274A639MK6KJ-gateway-sockets-must-never-d.md b/.lane/memory/apps/host/src/gateway.ts/01M50KBA3ME0Q9274A639MK6KJ-gateway-sockets-must-never-d.md
index e081a01b..5d9417a6 100644
--- a/.lane/memory/apps/host/src/gateway.ts/01M50KBA3ME0Q9274A639MK6KJ-gateway-sockets-must-never-d.md
+++ b/.lane/memory/apps/host/src/gateway.ts/01M50KBA3ME0Q9274A639MK6KJ-gateway-sockets-must-never-d.md
@@ -4,8 +4,9 @@ anchor: function websocket
 created: 2026-10-15T20:16:37Z
 norm: '1'
 sig: 1b462e5d3bc33728
-body_hash: aee7bf28626367fb
-raw_hash: 6675f75b614405d9
+body_hash: 39bbd535e37f47a0
+raw_hash: c1a585dfb617245a
+vouched: 2026-10-20T17:10:51Z
 lines: 673-737
 ---
 
diff --git a/.lane/memory/apps/host/src/gateway.ts/01M5D4BXMERGZ1EZ3EYAFM3YC4-worker-requests-worker-never.md b/.lane/memory/apps/host/src/gateway.ts/01M5D4BXMERGZ1EZ3EYAFM3YC4-worker-requests-worker-never.md
index 4ae0fc1d..4a35c64c 100644
--- a/.lane/memory/apps/host/src/gateway.ts/01M5D4BXMERGZ1EZ3EYAFM3YC4-worker-requests-worker-never.md
+++ b/.lane/memory/apps/host/src/gateway.ts/01M5D4BXMERGZ1EZ3EYAFM3YC4-worker-requests-worker-never.md
@@ -4,8 +4,9 @@ anchor: '@file'
 created: 2026-10-20T17:04:56Z
 norm: '1'
 sig: 1acdc0f6a0895ac5
-body_hash: 2cc87782e4d39750
-raw_hash: 2c0a05f043c689ac
+body_hash: f383b10cec21cd9b
+raw_hash: 9875bf699ce7d092
+vouched: 2026-10-20T17:10:51Z
 lines: 1-1153
 ---
 
diff --git a/apps/host/src/cli.ts b/apps/host/src/cli.ts
index 8c5fded2..40fe829b 100755
--- a/apps/host/src/cli.ts
+++ b/apps/host/src/cli.ts
@@ -84,8 +84,10 @@ const HELP = `ace — channels on this host
   ace directory [<url> | off]                    the team's directory, which lists every host's channels;
                                                  a running host checks it with ACE_SECRET first
   ace web [<url> | off]                          the deployed web app your devices may use with this host
-  ace serve [--port 4140] [--loopback]            serve the app and its WebSocket gateway;
-                                                 --loopback stays off the tailnet and the directory
+  ace serve [--port 4140] [--loopback] [--demo <script>]
+                                                serve the app and its WebSocket gateway;
+                                                 --loopback stays off the tailnet and the directory;
+                                                 --demo runs scripted synthetic teammates
   ace logs [--channel <ref>] [--trace <id>] [--level warn] [--since 10m] [--grep <text>]
            [-n 200] [--follow] [--json]              every process's logs, merged in time order
   ace open [--port 4140]                          open this host's authenticated app
@@ -122,6 +124,7 @@ const { values: flags, positionals } = parseArgs({
 		follow: { type: "boolean", short: "f" },
 		json: { type: "boolean" },
 		loopback: { type: "boolean" },
+		demo: { type: "string" },
 		help: { type: "boolean", short: "h" },
 	},
 });
@@ -488,7 +491,7 @@ async function main() {
 			return;
 		}
 		case "serve":
-			return serve(Number(flags.port || config.port), !!flags.loopback);
+			return serve(Number(flags.port || config.port), !!flags.loopback, flags.demo);
 		case "key": {
 			const name = rest[0];
 			if (!name || !/^[A-Z][A-Z0-9_]*$/.test(name)) {
diff --git a/apps/host/src/demo.ts b/apps/host/src/demo.ts
new file mode 100644
index 00000000..b52bf2de
--- /dev/null
+++ b/apps/host/src/demo.ts
@@ -0,0 +1,187 @@
+/**
+ * Demo mode: scripted synthetic teammates for recordings. They are present and act through the
+ * same paths real teammates do. Their messages, asks and reactions are ordinary channel requests
+ * that the channel admits by its own rules. Only their identities are made up, and only on this
+ * host: presence and people go to the owner's own app, never to the directory, lobbies or peers.
+ */
+import { readFileSync } from "node:fs";
+import { resolve } from "node:path";
+
+import type { Presence } from "@ace/directory/protocol";
+
+import type { Event } from "@ace/channel/protocol";
+
+import * as catalog from "./catalog";
+import { Connection, request } from "./client";
+import { failure, log } from "./log";
+import type { People } from "./protocol";
+
+type Person = {
+	/** The participant name their messages carry, like a Tailscale login. */
+	login: string;
+	/** Whose GitHub avatar and name the app shows for them. */
+	github: string;
+};
+
+type Target = { channel: string; chat?: number };
+
+/** `at` is seconds from the script's start; each step does one thing. */
+type Step =
+	& { at: number; who: string }
+	& (
+		| ({ open: true } & Target)
+		| ({ close: true } & Target)
+		| { away: boolean }
+		| { leave: true }
+		| ({ say: string } & Target)
+		| ({ ask: string } & Target)
+		/** Reacts to the chat's newest message or reply. */
+		| ({ react: string } & Target)
+	);
+
+export type Script = {
+	people: Record<string, Person>;
+	steps: Step[];
+	/** Seconds after the last step before the script starts over; once when absent. */
+	loop?: number;
+};
+
+type Here = { channels: Set<string>; away: boolean };
+
+let script: Script | undefined;
+const here = new Map<string, Here>();
+let project: (channel: string) => Promise<string>;
+let changed: () => void;
+/** Each listed channel's project, kept from each step so presence can be read synchronously. */
+const projects = new Map<string, string>();
+let timers: ReturnType<typeof setTimeout>[] = [];
+
+export function people(): People {
+	const found: People = {};
+	for (const person of Object.values(script?.people || {})) found[person.login] = person.github;
+	return found;
+}
+
+/** Synthetic people's presence by project, in the lobby's shape. */
+export function presence(): Record<string, Presence[]> {
+	const found: Record<string, Presence[]> = {};
+	for (const [who, state] of here) {
+		const person = script!.people[who]!;
+		const byProject = new Map<string, string[]>();
+		for (const channel of state.channels) {
+			const id = projects.get(channel);
+			if (!id) continue;
+			byProject.set(id, [...byProject.get(id) || [], channel]);
+		}
+		for (const [id, channels] of byProject) {
+			(found[id] ||= []).push({ login: person.github, host: "demo", channels, away: state.away });
+		}
+	}
+	return found;
+}
+
+function channelId(name: string): string {
+	const record = catalog.list().find((value) => value.name === name || value.id === name);
+	if (!record) throw new Error(`No channel ${name} on this host`);
+	return record.id;
+}
+
+async function present(who: string, target: Target) {
+	const id = channelId(target.channel);
+	projects.set(id, await project(id));
+	let state = here.get(who);
+	if (!state) here.set(who, state = { channels: new Set(), away: false });
+	state.channels.add(id);
+	state.away = false;
+	changed();
+	return id;
+}
+
+/** The chat's newest message or reply, read from the replayed transcript. */
+async function newest(id: string, chat?: number): Promise<number> {
+	const connection = await Connection.open(id);
+	try {
+		let entry: number | undefined;
+		const live = Promise.withResolvers<void>();
+		await connection.request({ op: "watch", ...(chat === undefined ? {} : { chat }) }, {
+			event(event: Event) {
+				if (event.kind === "message" || event.kind === "reply") entry = event.entry;
+				if (event.kind === "live") live.resolve();
+			},
+			closed: (error) => live.reject(new Error(error)),
+		});
+		await live.promise;
+		if (entry === undefined) throw new Error(`Nothing to react to in ${id}`);
+		return entry;
+	} finally {
+		connection.close();
+	}
+}
+
+async function run(step: Step) {
+	const person = script!.people[step.who];
+	if (!person) throw new Error(`No person ${step.who} in the script`);
+	const author = person.login;
+	if ("leave" in step) {
+		here.delete(step.who);
+		return changed();
+	}
+	if ("away" in step) {
+		const state = here.get(step.who);
+		if (state) state.away = step.away;
+		return changed();
+	}
+	if ("close" in step) {
+		here.get(step.who)?.channels.delete(channelId(step.channel));
+		return changed();
+	}
+	const id = await present(step.who, step);
+	const chat = step.chat === undefined ? {} : { chat: step.chat };
+	if ("say" in step) return void await request(id, { op: "say", author, text: step.say, ...chat });
+	// An ask returns once admitted; the run continues in the channel as anyone's would.
+	if ("ask" in step) return void await request(id, { op: "ask", author, text: step.ask, ...chat });
+	if ("react" in step) {
+		const entry = await newest(id, step.chat);
+		await request(id, { op: "react", author, entry, emoji: step.react, ...chat });
+	}
+}
+
+function schedule() {
+	const steps = [...script!.steps].sort((a, b) => a.at - b.at);
+	let last = 0;
+	for (const step of steps) {
+		last = Math.max(last, step.at);
+		timers.push(setTimeout(() => {
+			log("info", "demo.step", { who: step.who, at: step.at });
+			run(step).catch((error) =>
+				log("warn", "demo.step.failed", { at: step.at, ...failure(error) })
+			);
+		}, step.at * 1000));
+	}
+	if (script!.loop === undefined) return;
+	timers.push(setTimeout(() => {
+		timers = [];
+		here.clear();
+		changed();
+		schedule();
+	}, (last + script!.loop) * 1000));
+}
+
+/** Starts the script in `file`; the returned function stops it and takes everyone away. */
+export function start(
+	file: string,
+	options: { project(channel: string): Promise<string>; changed(): void },
+): () => void {
+	script = JSON.parse(readFileSync(resolve(file), "utf8")) as Script;
+	({ project, changed } = options);
+	log("info", "demo.start", { file, people: Object.keys(script.people).length });
+	console.log(`Demo mode: ${Object.keys(script.people).join(", ")} from ${file}`);
+	changed();
+	schedule();
+	return () => {
+		for (const timer of timers) clearTimeout(timer);
+		timers = [];
+		here.clear();
+		script = undefined;
+	};
+}
diff --git a/apps/host/src/gateway.ts b/apps/host/src/gateway.ts
index f5c8066c..eeda124a 100644
--- a/apps/host/src/gateway.ts
+++ b/apps/host/src/gateway.ts
@@ -10,6 +10,7 @@ import * as catalog from "./catalog";
 import { Connection } from "./client";
 import * as compute from "./compute";
 import { config } from "./config";
+import * as demo from "./demo";
 import { diagnostics } from "./diagnostics";
 import * as directory from "./directory";
 import { retryLoginShell, shell } from "./environment";
@@ -296,6 +297,7 @@ function people(): People {
 	const known: People = {};
 	for (const host of directory.read().hosts) if (host.github) known[host.login] = host.github;
 	Object.assign(known, peers.people());
+	Object.assign(known, demo.people());
 	const own = github.login(loginChanged);
 	if (own) known[catalog.user] = own;
 	return known;
@@ -355,9 +357,18 @@ function lobbyChanged(): void {
 
 let presenceSent = "";
 
+/** Lobby presence, with demo mode's synthetic people beside the real ones. */
+function present(): Record<string, Presence[]> {
+	const found = { ...lobby.presence() };
+	for (const [project, people] of Object.entries(demo.presence())) {
+		found[project] = [...found[project] || [], ...people];
+	}
+	return found;
+}
+
 /** Lobby presence reaches only the owner's app; peers never see it. */
 function presenceChanged(): void {
-	const frame = JSON.stringify({ presence: lobby.presence() } satisfies HostFrame);
+	const frame = JSON.stringify({ presence: present() } satisfies HostFrame);
 	if (frame === presenceSent) return;
 	presenceSent = frame;
 	for (const socket of sockets) if (!socket.data.peer) socket.send(frame);
@@ -828,7 +839,7 @@ function websocket(): Bun.WebSocketHandler<Client> {
 			void queue(async () => {
 				socket.send(JSON.stringify({ projects: await projects.list() } satisfies HostFrame));
 				socket.send(JSON.stringify({ people: people() } satisfies HostFrame));
-				socket.send(JSON.stringify({ presence: lobby.presence() } satisfies HostFrame));
+				socket.send(JSON.stringify({ presence: present() } satisfies HostFrame));
 			});
 		},
 		async message(socket, raw) {
@@ -1022,7 +1033,7 @@ async function listen(port: number): Promise<Server<Client>> {
  * entry, or lobby presence. A second host on this machine would otherwise publish under the
  * machine's tailnet name.
  */
-export async function serve(port: number, loopback = false): Promise<never> {
+export async function serve(port: number, loopback = false, script?: string): Promise<never> {
 	config.port = port;
 	config.loopback = loopback;
 	// Channel workers and agent shells reach this listener for the owner's windows.
@@ -1120,6 +1131,15 @@ export async function serve(port: number, loopback = false): Promise<never> {
 	} else if (!loopback) {
 		console.log("Tailscale is not running; channels stay on this machine");
 	}
+	if (script) {
+		cleanup.push(demo.start(script, {
+			project: projectOfChannel,
+			changed: () => {
+				peopleChanged();
+				presenceChanged();
+			},
+		}));
+	}
 	mkdirSync(join(catalog.home, "channels"), { recursive: true });
 	// Workers create and remove their sockets; tell clients when a channel starts or retires.
 	const watcher = watch(join(catalog.home, "channels"), { recursive: true }, (_, file) => {
diff --git a/docs/demo.md b/docs/demo.md
new file mode 100644
index 00000000..501656dd
--- /dev/null
+++ b/docs/demo.md
@@ -0,0 +1,37 @@
+# Demo mode
+
+`ace serve --demo <script.json>` runs scripted synthetic teammates on this host, for recordings.
+They are present in projects and channels, and they post, ask agents and react through ordinary
+channel requests, which each channel admits by its own rules: an ask needs the channel's agent
+access on, as a real teammate's would. Only their identities are made up, and only in the owner's
+own app; the directory, lobbies and peers never see them.
+
+Seed the channels first with `ace import` (see [channel data](data.md#seeds)).
+
+```json
+{
+	"people": {
+		"alex": { "login": "alex", "github": "octocat" }
+	},
+	"steps": [
+		{ "at": 0, "who": "alex", "open": true, "channel": "checkout" },
+		{ "at": 3, "who": "alex", "say": "pushed a fix, can someone check?", "channel": "checkout" },
+		{
+			"at": 6,
+			"who": "alex",
+			"ask": "does the fix handle a missing quantity?",
+			"channel": "checkout"
+		},
+		{ "at": 9, "who": "alex", "react": "👀", "channel": "checkout" },
+		{ "at": 30, "who": "alex", "away": true },
+		{ "at": 60, "who": "alex", "leave": true }
+	],
+	"loop": 30
+}
+```
+
+- `login` is the author their messages carry; `github` picks the avatar and name the app shows.
+- `at` is seconds from the start. `loop` restarts the script that many seconds after its last step.
+- Steps: `open`/`close` a channel (present there), `away` true or false, `leave`, `say`, `ask`, and
+  `react`, which reacts to the chat's newest message or reply. Acting opens the channel first.
+  `chat` targets a chat other than the root.