The host has a hand on the other seat: once the game begins, Seats makes a transfer phrase for the other player, which gives the seat a new token when claimed, and gives the seat of a player who cannot go on to a housecarl, who plays the move it owes at once; the player's token opens nothing while it stands in, their page goes to the gallery with the reason and a claim box, and a rematch holds their seat without the housecarl; the server pings every socket and closes one a dead browser left open

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0141G6xqLeNRYEtviLWSB5Up

deploy/hnefatafl-reseat.sh

@@ -19,7 +19,7 @@ r = json.load(sys.stdin)
 if "error" in r: sys.exit(r["error"])
 print("room %s, %s" % (r["roomId"], "in play" if r["started"] else "not begun"))
 for s in r["seats"]:
-    when = "bot" if s["bot"] else "never moved or spoke" if s["lastActed"] is None else "last acted " + datetime.datetime.fromtimestamp(s["lastActed"] / 1000, datetime.timezone.utc).strftime("%Y-%m-%d %H:%M UTC")
+    when = "bot" if s["bot"] else ("a housecarl stands in; " if s.get("standIn") else "") + ("never moved or spoke" if s["lastActed"] is None else "last acted " + datetime.datetime.fromtimestamp(s["lastActed"] / 1000, datetime.timezone.utc).strftime("%Y-%m-%d %H:%M UTC"))
     print("  %-3s %-24s %s" % (s["id"], s["name"], when))
 '
 else

deploy/hnefatafl-visitors.sh

@@ -42,7 +42,7 @@ for f in glob.glob("/var/lib/hnefatafl/rooms/*.jsonl"):
         continue
     created = datetime.datetime.fromtimestamp(meta["createdAt"] / 1000, datetime.timezone.utc)
     humans, bots_seated, started, turns, last, over, talk = [], [], False, 0, created, None, 0
-    names = {}
+    names, seat_changes = {}, []
     for x in lines[1:]:
         if x["t"] == "seat":
             (bots_seated if x["bot"] else humans).append(x["name"])
@@ -56,12 +56,16 @@ for f in glob.glob("/var/lib/hnefatafl/rooms/*.jsonl"):
             last = datetime.datetime.fromtimestamp(x["at"] / 1000, datetime.timezone.utc)
         elif x["t"] == "chat":
             talk += 1
+        elif x["t"] == "standIn":
+            seat_changes.append("%s %s's seat to a housecarl" % (datetime.datetime.fromtimestamp(x["at"] / 1000, datetime.timezone.utc).strftime("%H:%M"), names.get(x["id"], x["id"])))
+        elif x["t"] == "reseat":
+            seat_changes.append("%s %s re-seated" % (datetime.datetime.fromtimestamp(x["at"] / 1000, datetime.timezone.utc).strftime("%H:%M"), names.get(x["id"], x["id"])))
         elif x["t"] == "over":
             over = "a draw" if x["winner"] is None else "%s won" % names.get(x["winner"], x["winner"])
     for h in humans:
         if h not in first_seen or created < first_seen[h]:
             first_seen[h] = created
-    rooms.append(dict(id=meta["id"], size=meta["seats"], created=created, humans=humans, bots=bots_seated, started=started, turns=turns, last=last, over=over, talk=talk))
+    rooms.append(dict(id=meta["id"], size=meta["seats"], created=created, humans=humans, bots=bots_seated, started=started, turns=turns, last=last, over=over, talk=talk, seat_changes=seat_changes))
 
 today = sorted([r for r in rooms if r["created"].strftime("%F") == day], key=lambda r: r["created"])
 names = sorted({h for r in today for h in r["humans"]})
@@ -78,4 +82,6 @@ for r in today:
         r["created"].strftime("%H:%M"), r["id"], seated, (" (%d seat%s empty)" % (empty, "" if empty == 1 else "s")) if empty else "",
         state, r["turns"], span, r["last"].strftime("%H:%M") if r["turns"] else "never",
         ("  %d line%s of talk" % (r["talk"], "" if r["talk"] == 1 else "s")) if r["talk"] else ""))
+    for change in r["seat_changes"]:
+        print("        %s" % change)
 PY

docs/conventions.md

@@ -47,6 +47,18 @@ README.
   which asks for the key in `/etc/<slug>/keeper.key`, made by the deploy and
   readable by root and the game's user alone. A spectator at a game in play
   is told both ways back, and the hall asks before forgetting a game in play.
+- **The host has a hand on the other seats**: once the game begins, *Seats*
+  in the host's masthead makes a transfer phrase for another person's seat
+  (claimed, it gives the seat a new token, as the keeper's link does), and
+  gives the seat of a player who cannot go on to a housecarl, who plays it
+  from the move the seat owes and does not speak in the person's name.
+  The person's token opens nothing while one stands in, with the reason;
+  their page goes to the gallery, where a claim box takes the host's
+  phrase. A rematch holds the person's seat and leaves the stand-in out.
+- **A dead browser's socket is closed**: the server pings every socket on
+  the protocol's own ping, which browsers answer by themselves, and closes
+  one silent for a whole round, so a crashed tab does not linger in the
+  gallery's count.
 - **Held seats are doubted before they are dropped**: the hall forgets a
   seat only on the second refusal in a row from the server. A restart, a
   stale answer or the wrong backend answer with ignorance, and ignorance

server/src/index.ts

@@ -14,6 +14,8 @@
 //   POST /api/rooms/:id/challenge   {token}            call the keeper to a held seat; their phone rings
 //   POST /api/rooms/:id/rematch     {token}            a finished table opens the next one
 //   POST /api/rooms/:id/transfer    {token}            mint a phrase that carries this seat to another device
+//   POST /api/rooms/:id/phrase      {token, seat}      the host mints one for another person's seat, which re-seats it when claimed
+//   POST /api/rooms/:id/standin     {token, seat}      the host gives a person's seat to a bot for the rest of the game
 //   POST /api/transfer              {phrase}           claim one
 //   POST /api/rooms/:id/report      {token?, happened, expected}  a report to the keeper, pinned to the round
 //   POST /api/reports/:id/image     <image bytes>      a screenshot for a report just filed
@@ -81,6 +83,8 @@ const bells = new RateLimit(3, 60 * 60 * 1000);
 /** Claims on transfer phrases: a phrase is guessed, not brute-forced. */
 const claims = new RateLimit(10, 10 * 60 * 1000);
 const MAX_AUDIENCE = 30;
+/** How often each socket is asked to answer; one silent through a whole round is a browser gone, and is closed. */
+const PING_MS = Number(process.env.PING_MS ?? 30_000);
 const IDLE_ROOM_MS = 7 * 24 * 60 * 60 * 1000;
 setInterval(() => {
 	const n = rooms.evictIdle(IDLE_ROOM_MS);
@@ -307,6 +311,13 @@ async function handle(req: IncomingMessage, res: ServerResponse): Promise<void>
 	if (action === 'transfer') {
 		return send(res, 200, rooms.transfer(room, token));
 	}
+	if (action === 'phrase') {
+		return send(res, 200, rooms.hostPhrase(room, token, body.seat));
+	}
+	if (action === 'standin') {
+		rooms.standIn(room, token, body.seat);
+		return send(res, 200, rooms.view(room, rooms.seatOf(room, token).id));
+	}
 	if (action === 'report') {
 		if (!desk.allow(clientOf(req))) throw new RoomError(DESK_BUSY, 429);
 		const seat = token ? rooms.seatOf(room, token) : null;
@@ -352,11 +363,30 @@ server.on('upgrade', (req, socket, head) => {
 		};
 		const unsubscribe = seatId === SPECTATOR ? rooms.watch(room, onChange) : rooms.subscribe(room.id, onChange);
 		ws.on('close', unsubscribe);
+		answered.set(ws, true);
+		ws.on('pong', () => answered.set(ws, true));
 		// A socket's own error (a message over the limit, a malformed frame) closes that socket, never the server.
 		ws.on('error', () => ws.terminate());
 	});
 });
 
+/**
+ * A browser that died without closing (a crashed tab, a sleeping laptop, a dropped network) leaves its socket
+ * open until TCP gives up, counted in the gallery all the while. The protocol's own ping, which every browser
+ * answers by itself, finds it within two rounds.
+ */
+const answered = new WeakMap<WebSocket, boolean>();
+setInterval(() => {
+	for (const ws of wss.clients) {
+		if (!answered.get(ws)) {
+			ws.terminate();
+			continue;
+		}
+		answered.set(ws, false);
+		ws.ping();
+	}
+}, PING_MS).unref();
+
 server.listen(PORT, HOST, () => {
 	console.log(`hnefatafl server listening on http://${HOST}:${PORT}, rooms in ${DATA_DIR}`);
 });

server/src/rooms.test.ts

@@ -49,3 +49,58 @@ describe('rooms', () => {
 		expect(seats.find((s) => s.id !== mover)!.lastActed).toBeNull();
 	});
 });
+
+describe('the host and the other seat', () => {
+	it("gives a person's seat to a housecarl, who plays it whenever it owes the move, and the person's token opens nothing", () => {
+		const { rooms, room, ann, bo } = table();
+		rooms.standIn(room, ann, 'B');
+		expect(() => rooms.seatOf(room, bo)).toThrow(/gave your seat to a housecarl/);
+		expect(rooms.view(room, 'A').seats[1]).toEqual({ id: 'B', name: 'Bo', bot: true, standIn: true });
+		// Whoever moved first, the housecarl has answered, and the move is Ann's.
+		expect(rooms.waitingOn(room)).toEqual(['A']);
+		const before = room.resolved;
+		rooms.submit(room, ann, game.botInput(room.state!, 'A'), room.resolved);
+		expect(room.resolved).toBe(before + 2);
+		expect(rooms.waitingOn(room)).toEqual(['A']);
+	});
+
+	it("is the host's call alone, in a game under way, for the other person", () => {
+		const { rooms, room, ann, bo } = table();
+		expect(() => rooms.standIn(room, bo, 'A')).toThrow(/Only the player who opened/);
+		expect(() => rooms.standIn(room, ann, 'A')).toThrow(/keeps their own seat/);
+		expect(() => rooms.standIn(room, ann, 'Z')).toThrow(/No person sits/);
+		const lobby = rooms.create('Ann', 2);
+		rooms.join(lobby.room, 'Bo');
+		expect(() => rooms.standIn(lobby.room, lobby.token, 'B')).toThrow(/under way/);
+	});
+
+	it("gives the seat back by the host's phrase, with a new token, and a restart keeps both changes", () => {
+		const { rooms, room, ann, bo } = table();
+		rooms.standIn(room, ann, 'B');
+		expect(new Rooms(game, new Store(dir)).get(room.id).seats[1]).toMatchObject({ bot: true, standIn: true });
+		const claimed = rooms.claim(rooms.hostPhrase(room, ann, 'B').phrase);
+		expect(claimed.seat).toBe('B');
+		expect(rooms.seatOf(room, claimed.token).name).toBe('Bo');
+		expect(() => rooms.seatOf(room, bo)).toThrow(/opens no seat/);
+		const reopened = new Rooms(game, new Store(dir)).get(room.id);
+		expect(reopened.seats[1]).toEqual({ id: 'B', name: 'Bo', tokenHash: room.seats[1].tokenHash, bot: false });
+	});
+
+	it("re-seats a person whose browser lost the seat, by the host's phrase, once, and only the host makes one", () => {
+		const { rooms, room, ann, bo } = table();
+		expect(() => rooms.hostPhrase(room, bo, 'A')).toThrow(/Only the player who opened/);
+		expect(() => rooms.hostPhrase(room, ann, 'A')).toThrow(/No other person/);
+		const { phrase } = rooms.hostPhrase(room, ann, 'B');
+		const claimed = rooms.claim(phrase);
+		expect(claimed.token).not.toBe(bo);
+		expect(() => rooms.seatOf(room, bo)).toThrow(/opens no seat/);
+		expect(() => rooms.claim(phrase)).toThrow(/unknown or has expired/);
+	});
+
+	it("voids a phrase for the seat once a housecarl stands in", () => {
+		const { rooms, room, ann } = table();
+		const { phrase } = rooms.hostPhrase(room, ann, 'B');
+		rooms.standIn(room, ann, 'B');
+		expect(() => rooms.claim(phrase)).toThrow(/unknown or has expired/);
+	});
+});

server/src/rooms.ts

@@ -17,9 +17,12 @@ export { SPECTATOR };
 export interface Seat {
 	id: SeatId;
 	name: string;
-	/** SHA-256 of the seat's token, hex; empty for a bot. */
+	/** SHA-256 of the seat's token, hex; empty for a bot. A seat a bot stands in for keeps the person's, which opens nothing while it does. */
 	tokenHash: string;
+	/** A bot plays this seat: one seated as a bot, or one standing in for a person. */
 	bot: boolean;
+	/** The host gave this person's seat to a bot; a phrase from the host, or the keeper, gives it back. */
+	standIn?: true;
 }
 
 function hashToken(token: string): string {
@@ -108,8 +111,8 @@ export class Rooms<State, Input> {
 	private listeners = new Map<string, Set<(room: Room<State>) => void>>();
 	/** Sockets watching from the gallery, by room. */
 	private gallery = new Map<string, number>();
-	/** Phrases waiting to be claimed, with the seat and the token they carry. */
-	private transfers = new Map<string, { roomId: string; seatId: SeatId; token: string; expiresAt: number }>();
+	/** Phrases waiting to be claimed, with the seat and the token they carry; the host's carry none, and re-seat on claim. */
+	private transfers = new Map<string, { roomId: string; seatId: SeatId; token: string | null; expiresAt: number }>();
 	private failedClaims = 0;
 	private failWindowStart = 0;
 
@@ -168,7 +171,8 @@ export class Rooms<State, Input> {
 	seatOf(room: Room<State>, token: string | undefined): Seat {
 		if (!token) throw new RoomError('That token opens no seat at this game.', 403);
 		const given = Buffer.from(hashToken(token), 'hex');
-		const seat = room.seats.find((s) => !s.bot && s.tokenHash.length === given.length * 2 && timingSafeEqual(Buffer.from(s.tokenHash, 'hex'), given));
+		const seat = room.seats.find((s) => s.tokenHash.length === given.length * 2 && timingSafeEqual(Buffer.from(s.tokenHash, 'hex'), given));
+		if (seat?.standIn) throw new RoomError('The host gave your seat to a housecarl, who plays on in your place. Ask them for a transfer phrase to take it back.', 403);
 		if (!seat) throw new RoomError('That token opens no seat at this game.', 403);
 		return seat;
 	}
@@ -257,9 +261,10 @@ export class Rooms<State, Input> {
 		const caller = this.seatOf(room, token);
 		if (!room.state || !this.game.over(room.state)) throw new RoomError('The game is not over yet.', 409);
 		if (room.rematch) return { roomId: room.rematch.to, seat: null, token: null, created: false };
-		const others = room.seats.filter((s) => !s.bot && s.id !== caller.id).map((s) => s.name);
+		// A person a bot stood in for is still one of the company; the stand-in does not follow.
+		const others = room.seats.filter((s) => (!s.bot || s.standIn) && s.id !== caller.id).map((s) => s.name);
 		const next = this.open(caller.name, room.size, room.options, { rematchOf: room.id, expected: others });
-		for (const bot of room.seats.filter((s) => s.bot)) this.sit(next.room, bot.name, true);
+		for (const bot of room.seats.filter((s) => s.bot && !s.standIn)) this.sit(next.room, bot.name, true);
 		this.commit(room, { t: 'rematch', at: Date.now(), to: next.room.id, by: caller.id });
 		return { roomId: next.room.id, seat: next.seat, token: next.token, created: true };
 	}
@@ -267,6 +272,22 @@ export class Rooms<State, Input> {
 	/** Mint a phrase that brings this seat to another device: four words, ten minutes, one use. */
 	transfer(room: Room<State>, token: string | undefined): { phrase: string; expiresAt: number } {
 		const seat = this.seatOf(room, token);
+		return this.mint(room.id, seat.id, token!);
+	}
+
+	/**
+	 * The host mints a phrase for another person's seat: for a player whose browser lost it, or to take it back
+	 * from a housecarl standing in. Claimed, it gives the seat a new token, so the old one opens nothing after.
+	 */
+	hostPhrase(room: Room<State>, token: string | undefined, seatId: unknown): { phrase: string; expiresAt: number } {
+		const host = this.seatOf(room, token);
+		if (host.id !== room.seats[0]?.id) throw new RoomError('Only the player who opened the table may make a phrase for another seat.', 403);
+		const seat = room.seats.find((s) => s.id === seatId && s.id !== host.id && (!s.bot || s.standIn));
+		if (!seat) throw new RoomError('No other person sits in that seat.', 404);
+		return this.mint(room.id, seat.id, null);
+	}
+
+	private mint(roomId: string, seatId: SeatId, token: string | null): { phrase: string; expiresAt: number } {
 		const now = Date.now();
 		for (const [phrase, t] of this.transfers) if (t.expiresAt < now) this.transfers.delete(phrase);
 		if (this.transfers.size >= 200) throw new RoomError('Too many transfers are pending; try again in a few minutes.', 429);
@@ -275,7 +296,7 @@ export class Rooms<State, Input> {
 			phrase = Array.from({ length: 4 }, () => TRANSFER_WORDS[randomBytes(1)[0] % TRANSFER_WORDS.length]).join('-');
 		} while (this.transfers.has(phrase));
 		const expiresAt = now + TRANSFER_TTL_MS;
-		this.transfers.set(phrase, { roomId: room.id, seatId: seat.id, token: token!, expiresAt });
+		this.transfers.set(phrase, { roomId, seatId, token, expiresAt });
 		return { phrase, expiresAt };
 	}
 
@@ -296,6 +317,10 @@ export class Rooms<State, Input> {
 		}
 		this.transfers.delete(phrase);
 		const room = this.get(t.roomId);
+		if (t.token === null) {
+			const { seat, token } = this.reseat(room, t.seatId);
+			return { roomId: room.id, seat: seat.id, token };
+		}
 		const seat = this.seatOf(room, t.token);
 		return { roomId: room.id, seat: seat.id, token: t.token };
 	}
@@ -351,27 +376,49 @@ export class Rooms<State, Input> {
 	}
 
 	/**
-	 * The keeper gives a person's seat a new token, for a player whose browser lost the old one. Whether the one
-	 * asking holds the seat is the keeper's judgment; this carries it out. The old token opens nothing after.
+	 * A person's seat gets a new token, for a player whose browser lost the old one, or one taking it back from a
+	 * bot standing in. Whether the one asking holds the seat is the keeper's judgment, or the host's in the phrase
+	 * they made; this carries it out. The old token opens nothing after.
 	 */
 	reseat(room: Room<State>, seatId: unknown): { seat: Seat; token: string } {
-		const seat = room.seats.find((s) => s.id === seatId && !s.bot);
+		const seat = room.seats.find((s) => s.id === seatId && (!s.bot || s.standIn));
 		if (!seat) throw new RoomError('No person sits in that seat.', 404);
 		const token = newId(18);
 		this.commit(room, { t: 'reseat', at: Date.now(), id: seat.id, tokenHash: hashToken(token) });
-		// A phrase minted with the old token would carry a seat that no longer answers to it.
-		for (const [phrase, t] of this.transfers) if (t.roomId === room.id && t.seatId === seat.id) this.transfers.delete(phrase);
+		this.voidPhrases(room, seat.id);
 		return { seat, token };
 	}
 
+	/**
+	 * The host gives a person's seat to a bot, for a player who cannot go on: the bot plays it from the next move
+	 * the seat owes, and the person's token opens nothing until a phrase from the host gives it back.
+	 */
+	standIn(room: Room<State>, token: string | undefined, seatId: unknown): void {
+		const host = this.seatOf(room, token);
+		if (host.id !== room.seats[0]?.id) throw new RoomError('Only the player who opened the table may give a seat to a housecarl.', 403);
+		if (!room.state || this.game.over(room.state)) throw new RoomError('Only a game under way needs a stand-in.', 409);
+		if (seatId === host.id) throw new RoomError('The host keeps their own seat.', 409);
+		const seat = room.seats.find((s) => s.id === seatId && !s.bot);
+		if (!seat) throw new RoomError('No person sits in that seat.', 404);
+		this.commit(room, { t: 'standIn', at: Date.now(), id: seat.id, by: host.id });
+		this.voidPhrases(room, seat.id);
+		// The move may have been this seat's.
+		if (this.waitingOn(room).length === 0) this.resolve(room);
+	}
+
+	/** A phrase minted for a seat whose token has changed hands would carry a seat that no longer answers to it. */
+	private voidPhrases(room: Room<State>, seatId: SeatId): void {
+		for (const [phrase, t] of this.transfers) if (t.roomId === room.id && t.seatId === seatId) this.transfers.delete(phrase);
+	}
+
 	/** The table as the keeper sees it before re-seating: who sits where, and when each person last moved or spoke. */
-	seatsForKeeper(room: Room<State>): { id: SeatId; name: string; bot: boolean; lastActed: number | null }[] {
+	seatsForKeeper(room: Room<State>): { id: SeatId; name: string; bot: boolean; standIn: boolean; lastActed: number | null }[] {
 		const last = new Map<SeatId, number>();
 		for (const line of this.store.read(room.id)) {
 			if (line.t === 'input' || line.t === 'chat') last.set(line.id, line.at);
 			else if (line.t === 'turn') for (const id of Object.keys(line.inputs)) last.set(id, line.at);
 		}
-		return room.seats.map((s) => ({ id: s.id, name: s.name, bot: s.bot, lastActed: s.bot ? null : (last.get(s.id) ?? null) }));
+		return room.seats.map((s) => ({ id: s.id, name: s.name, bot: s.bot && !s.standIn, standIn: !!s.standIn, lastActed: s.bot && !s.standIn ? null : (last.get(s.id) ?? null) }));
 	}
 
 	/** The host sends a bot away before the game begins. People leave by not coming back. */
@@ -407,7 +454,8 @@ export class Rooms<State, Input> {
 
 	private resolve(room: Room<State>): void {
 		const inputs: Record<SeatId, unknown> = { ...room.pending };
-		for (const seat of room.seats) if (seat.bot && this.game.needsInput(room.state!, seat.id)) inputs[seat.id] = this.game.botInput(room.state!, seat.id);
+		// A move the person made before a bot stood in for them stands.
+		for (const seat of room.seats) if (seat.bot && this.game.needsInput(room.state!, seat.id) && !(seat.id in inputs)) inputs[seat.id] = this.game.botInput(room.state!, seat.id);
 		this.commit(room, { t: 'turn', at: Date.now(), inputs });
 		this.driveBots(room);
 	}
@@ -444,7 +492,7 @@ export class Rooms<State, Input> {
 			size: room.size,
 			me: seatId,
 			host: room.seats[0]?.id ?? seatId,
-			seats: room.seats.map((s) => ({ id: s.id, name: s.name, bot: s.bot })),
+			seats: room.seats.map((s) => ({ id: s.id, name: s.name, bot: s.bot, ...(s.standIn ? { standIn: true as const } : {}) })),
 			waitingOn: this.waitingOn(room),
 			turn: room.state ? this.game.turn(room.state) : null,
 			resolved: room.resolved,
@@ -512,7 +560,17 @@ export class Rooms<State, Input> {
 				break;
 			case 'reseat': {
 				const seat = room.seats.find((s) => s.id === line.id);
-				if (seat) seat.tokenHash = line.tokenHash;
+				if (!seat) break;
+				seat.tokenHash = line.tokenHash;
+				seat.bot = false;
+				delete seat.standIn;
+				break;
+			}
+			case 'standIn': {
+				const seat = room.seats.find((s) => s.id === line.id);
+				if (!seat) break;
+				seat.bot = true;
+				seat.standIn = true;
 				break;
 			}
 			case 'galleryTalk':

server/src/store.ts

@@ -11,8 +11,13 @@ export type LedgerLine =
 	| { t: 'room'; id: string; seats: number; createdAt: number; rematchOf?: string; expected?: string[]; options: TableOptions }
 	/** A seat holds only the hash of its token; the token itself goes once to the browser that earned it. A bot's hash is empty. */
 	| { t: 'seat'; id: SeatId; name: string; tokenHash: string; bot: boolean }
-	/** The keeper gave a person's seat a new token, for a player whose browser lost the old one; the old one opens nothing after. */
+	/**
+	 * A person's seat got a new token, from the keeper or a phrase the host made, for a player whose browser lost the
+	 * old one; the old one opens nothing after. A seat a housecarl was standing in for is the person's again.
+	 */
 	| { t: 'reseat'; at: number; id: SeatId; tokenHash: string }
+	/** The host gave a person's seat to a housecarl, who plays it from here on; a reseat gives it back. */
+	| { t: 'standIn'; at: number; id: SeatId; by: SeatId }
 	/** One seat's move for the round in progress, so a restart keeps it. The turn line that follows carries every input again. */
 	| { t: 'input'; at: number; id: SeatId; input: unknown }
 	/** A bot sent away by the host before the game began; its seat id is free again. */

src/lib/components/Hall.svelte

@@ -162,7 +162,7 @@
 		const g = games[held.roomId];
 		if (g === undefined) return 'looking';
 		if (g === null) return 'unreachable';
-		const others = g.seats.filter((s) => s.id !== held.seat).map((s) => (s.bot ? `${s.name} (a housecarl)` : s.name));
+		const others = g.seats.filter((s) => s.id !== held.seat).map((s) => (s.standIn ? `${s.name} (a housecarl stands in)` : s.bot ? `${s.name} (a housecarl)` : s.name));
 		if (!g.state) return `waiting to start${g.seats.length ? ` · ${g.seats.map((s) => s.name).join(', ')}` : ''}`;
 		if (g.over) {
 			if (g.over.winner === held.seat) return 'you won';

src/lib/components/SeatsSlip.svelte

@@ -0,0 +1,154 @@
+<script lang="ts">
+	// The host's hand on the other seats during a game: a transfer phrase for a
+	// player whose browser lost their seat, and a housecarl to play the seat of one
+	// who cannot go on, until a phrase gives it back.
+	import type { SeatId } from '$lib/game/spec';
+	import type { Room } from '$lib/net/room.svelte';
+
+	let { room, open = $bindable(false) }: { room: Room; open?: boolean } = $props();
+
+	const people = $derived(room.view.seats.filter((s) => s.id !== room.me && (!s.bot || s.standIn)));
+	let asked = $state<SeatId | null>(null);
+	let phrase = $state<{ name: string; phrase: string; expiresAt: number } | null>(null);
+	let error = $state('');
+
+	function close() {
+		open = false;
+		asked = null;
+		error = '';
+	}
+
+	async function makePhrase(seat: SeatId, name: string) {
+		error = '';
+		try {
+			const made = await room.hostPhrase(seat);
+			phrase = { name, ...made };
+			setTimeout(() => {
+				if (phrase?.phrase === made.phrase) phrase = null;
+			}, Math.max(0, made.expiresAt - Date.now()));
+		} catch (e) {
+			error = e instanceof Error ? e.message : 'The phrase could not be made.';
+		}
+	}
+
+	async function standIn(seat: SeatId) {
+		asked = null;
+		if (!(await room.standIn(seat))) error = room.error;
+	}
+
+	function phraseTitle(name: string, standIn: boolean): string {
+		const why = standIn ? `Brings ${name} back from the housecarl.` : `For when ${name}'s browser lost the seat, or they need to play from another device.`;
+		return `${why} You get four words to pass to them. Within ten minutes, they enter them in the hall, or in the claim box while watching this table, and sit back down as ${name}. The phrase works once, and the browser they used before stops opening the seat.`;
+	}
+</script>
+
+<svelte:window onkeydown={(e) => open && e.key === 'Escape' && close()} />
+
+{#if open}
+	<div class="scrim" role="presentation" onclick={(ev) => ev.target === ev.currentTarget && close()}>
+		<div class="slip" role="dialog" aria-labelledby="seats-heading">
+			<h2 id="seats-heading">The other seats</h2>
+			<p class="muted small">As the host, you can bring a player back to a seat their browser lost, or give the seat of one who cannot go on to a housecarl, who plays it at once.</p>
+			{#if people.length === 0}
+				<p class="muted">Nobody else at this table is a person.</p>
+			{/if}
+			<ul>
+				{#each people as s (s.id)}
+					<li>
+						<span class="name">{s.name}{#if s.standIn}<span class="muted note">a housecarl plays for them</span>{/if}</span>
+						<span class="ways">
+							<button type="button" class="quiet" title={phraseTitle(s.name, !!s.standIn)} onclick={() => makePhrase(s.id, s.name)}>{s.standIn ? 'Transfer phrase to take it back' : 'Make a transfer phrase'}</button>
+							{#if !s.standIn && !room.view.over}
+								{#if asked === s.id}
+									<button type="button" class="commit small" onclick={() => standIn(s.id)}>Yes, a housecarl plays for {s.name}</button>
+									<button type="button" class="link" onclick={() => (asked = null)}>no</button>
+								{:else}
+									<button type="button" class="quiet" title="A housecarl plays {s.name}'s seat from their next move, and their browser stops opening it. A transfer phrase gives it back." onclick={() => (asked = s.id)}>Give to a housecarl</button>
+								{/if}
+							{/if}
+						</span>
+					</li>
+				{/each}
+			</ul>
+			{#if phrase}
+				<p class="made">Give {phrase.name} this phrase to claim within ten minutes, in the hall or while watching this table: <b class="phrase">{phrase.phrase}</b>. It works once, and their old link stops opening the seat.</p>
+			{/if}
+			{#if error}<p class="warning">{error}</p>{/if}
+			<div class="actions"><button type="button" class="link" onclick={close}>close</button></div>
+		</div>
+	</div>
+{/if}
+
+<style>
+	.scrim {
+		position: fixed;
+		inset: 0;
+		z-index: 20;
+		background: rgba(0, 0, 0, 0.55);
+		display: grid;
+		grid-template-rows: minmax(0, 1fr);
+		place-items: center;
+		padding: 16px;
+	}
+
+	.slip {
+		width: min(100%, 34rem);
+		max-height: 100%;
+		overflow-y: auto;
+		background: var(--slate);
+		border: 1px solid var(--rule-strong);
+		border-radius: 6px;
+		padding: 1rem 1.2rem 1.2rem;
+	}
+
+	h2 {
+		font-size: 1.3rem;
+		margin-bottom: 0.4rem;
+	}
+
+	ul {
+		list-style: none;
+		padding: 0;
+		margin: 0.8rem 0 0;
+	}
+
+	li {
+		display: flex;
+		flex-wrap: wrap;
+		align-items: center;
+		justify-content: space-between;
+		gap: 0.4rem 1rem;
+		padding: 0.5rem 0;
+		border-bottom: 1px solid var(--rule);
+	}
+
+	.note {
+		margin-left: 0.5em;
+		font-style: italic;
+		font-size: 0.9em;
+	}
+
+	.ways {
+		display: flex;
+		flex-wrap: wrap;
+		align-items: center;
+		gap: 0.5rem;
+	}
+
+	.made {
+		margin-top: 0.8rem;
+	}
+
+	.phrase {
+		letter-spacing: 0.06em;
+		user-select: all;
+	}
+
+	.warning {
+		margin-top: 0.5rem;
+	}
+
+	.actions {
+		margin-top: 0.9rem;
+	}
+</style>

src/lib/net/client.ts

@@ -146,6 +146,9 @@ export function makeApi<State, Input>() {
 		rematch: (roomId: string, token: string) =>
 			call<{ roomId: string; seat: SeatId | null; token: string | null; created: boolean }>('POST', `/api/rooms/${roomId}/rematch`, { token }),
 		transfer: (roomId: string, token: string) => call<{ phrase: string; expiresAt: number }>('POST', `/api/rooms/${roomId}/transfer`, { token }),
+		/** The host's phrase for another person's seat; claimed, it re-seats them. */
+		hostPhrase: (roomId: string, token: string, seat: SeatId) => call<{ phrase: string; expiresAt: number }>('POST', `/api/rooms/${roomId}/phrase`, { token, seat }),
+		standIn: (roomId: string, token: string, seat: SeatId) => call<View>('POST', `/api/rooms/${roomId}/standin`, { token, seat }),
 		claim: (phrase: string) => call<{ roomId: string; seat: SeatId; token: string }>('POST', '/api/transfer', { phrase }),
 		report: (roomId: string, token: string, happened: string, expected: string) =>
 			call<{ id: string }>('POST', `/api/rooms/${roomId}/report`, { token, happened, expected }),

src/lib/net/room.svelte.ts

@@ -5,7 +5,7 @@
 import { game } from '$lib/game';
 import { SPECTATOR, type SeatId, type TableOptions } from '$lib/game/spec';
 import type { Input, State } from '$lib/game';
-import { makeApi, rememberSeat, watchRoom, type HeldSeat } from './client';
+import { makeApi, rememberSeat, ServerError, watchRoom, type HeldSeat } from './client';
 import { markTalkSeen } from './talk';
 import type { RoomView } from './view';
 
@@ -38,6 +38,8 @@ export class Room {
 	error = $state('');
 	/** A move is on its way to the server. */
 	sending = $state(false);
+	/** The server stopped taking this seat's token while the page was open, and why; the page goes to the gallery. */
+	lost = $state('');
 
 	constructor(view: RoomView<State>, token: string) {
 		this.view = view;
@@ -72,7 +74,10 @@ export class Room {
 		const refresh = () => {
 			fetchView()
 				.then((v) => this.apply(v))
-				.catch((e: Error) => (this.error = e.message));
+				.catch((e: Error) => {
+					if (e instanceof ServerError && e.status === 403 && !this.spectating) this.lost = e.message;
+					else this.error = e.message;
+				});
 		};
 		return watchRoom(this.roomId, this.token, refresh, (open) => (this.connected = open));
 	}
@@ -134,6 +139,16 @@ export class Room {
 		return api.transfer(this.roomId, this.token);
 	}
 
+	/** Host only: a phrase for another person's seat, which gives it a new token when claimed. */
+	hostPhrase(seat: SeatId): Promise<{ phrase: string; expiresAt: number }> {
+		return api.hostPhrase(this.roomId, this.token, seat);
+	}
+
+	/** Host only: a housecarl plays this person's seat for the rest of the game, until a phrase gives it back. */
+	standIn(seat: SeatId): Promise<boolean> {
+		return this.act(() => api.standIn(this.roomId, this.token, seat), 'The seat could not be given to a housecarl.');
+	}
+
 	async submit(input: Input): Promise<boolean> {
 		this.sending = true;
 		try {

src/lib/net/view.ts

@@ -20,7 +20,8 @@ export interface RoomView<State> {
 	me: SeatId;
 	/** The player who opened the table and may begin the game. */
 	host: SeatId;
-	seats: { id: SeatId; name: string; bot: boolean }[];
+	/** Who sits where; `standIn` marks a person's seat the host gave to a bot, which plays it until they take it back. */
+	seats: { id: SeatId; name: string; bot: boolean; standIn?: true }[];
 	/** Seats that still have to move before the round resolves. */
 	waitingOn: SeatId[];
 	/** Rounds played so far; a move is sent with the count it was made against. */

src/routes/guide/+page.svelte

@@ -35,7 +35,7 @@
 		<h2>The table</h2>
 		<p>
 			Whoever opened the table is its host, and begins the game once a second player has sat or a housecarl has been seated. A friend who opens the link takes the other seat. The
-			masthead's <em>Transfer seat</em> gives four words that bring your seat to another device, and when a game is over anyone at the table may call for a rematch.
+			masthead's <em>Transfer seat</em> gives four words that bring your seat to another device, and when a game is over anyone at the table may call for a rematch. During a game the host's <em>Seats</em> makes the same four words for the other player, if their browser loses the seat, and can hand that seat to a housecarl when they cannot go on. Their four words bring them back.
 		</p>
 	</section>
 

src/routes/join/[code]/+page.svelte

@@ -4,9 +4,10 @@
 	import Board from '$lib/components/Board.svelte';
 	import Lobby from '$lib/components/Lobby.svelte';
 	import ReportSlip from '$lib/components/ReportSlip.svelte';
+	import SeatsSlip from '$lib/components/SeatsSlip.svelte';
 	import Preferences from '$lib/components/Preferences.svelte';
 	import { rememberSeat, seatFor, seatInLink, ServerError, trustSeat, type HeldSeat } from '$lib/net/client';
-	import { NAME_MAX, playerName, rememberName, Room } from '$lib/net/room.svelte';
+	import { api, NAME_MAX, playerName, rememberName, Room } from '$lib/net/room.svelte';
 
 	const roomId = $derived((page.params.code ?? '').toUpperCase());
 
@@ -21,6 +22,11 @@
 	/** A phrase minted to carry this seat to another device, while it lasts. */
 	let phrase = $state<{ phrase: string; expiresAt: number } | null>(null);
 	let rematching = $state(false);
+	let seatsOpen = $state(false);
+	/** Why this browser's seat no longer opens, when the server said so; shown while watching. */
+	let seatLost = $state('');
+	let claimPhrase = $state('');
+	let claiming = $state(false);
 
 	const link = $derived(`${location.origin}/join/${roomId}`);
 	const watching = $derived(room?.spectating ?? false);
@@ -44,7 +50,17 @@
 			});
 		// Only the server's refusal of the held token lets a link in: a dropped connection is not a lost seat.
 		const refused = (e: unknown) => e instanceof ServerError && e.status === 403;
-		const arrive = held ? Room.resume(id, held).catch((e: Error) => (sent && refused(e) ? take(sent) : Promise.reject(e))) : sent ? take(sent).catch(() => Room.watch(id)) : Room.watch(id);
+		// A held seat the server refuses, with no link to replace it, is watched from the gallery, with the reason.
+		const watchRefused = (e: Error) => {
+			seatLost = e.message;
+			return Room.watch(id);
+		};
+		seatLost = '';
+		const arrive = held
+			? Room.resume(id, held).catch((e: Error) => (sent && refused(e) ? take(sent) : refused(e) ? watchRefused(e) : Promise.reject(e)))
+			: sent
+				? take(sent).catch(() => Room.watch(id))
+				: Room.watch(id);
 		joining = !held && !sent;
 		if (!held) name = playerName();
 		arrive
@@ -62,6 +78,36 @@
 		return r.connect();
 	});
 
+	// The seat stopped opening while the page was open (the host gave it to a housecarl): watch on from the gallery.
+	$effect(() => {
+		const r = room;
+		if (!r?.lost) return;
+		seatLost = r.lost;
+		Room.watch(r.roomId)
+			.then((w) => (room = w))
+			.catch((e: Error) => (error = e.message));
+	});
+
+	/** Sit back down by a phrase: the host's, or one this seat minted on another device. */
+	async function claim(e: SubmitEvent) {
+		e.preventDefault();
+		claiming = true;
+		error = '';
+		try {
+			const got = await api.claim(claimPhrase.trim());
+			rememberSeat(got.roomId, { seat: got.seat, token: got.token });
+			trustSeat(got.roomId);
+			claimPhrase = '';
+			seatLost = '';
+			if (got.roomId === roomId) room = await Room.resume(roomId, { seat: got.seat, token: got.token });
+			else await goto(`/join/${got.roomId}`);
+		} catch (err) {
+			error = err instanceof Error ? err.message : 'The phrase could not be claimed.';
+		} finally {
+			claiming = false;
+		}
+	}
+
 	async function takeSeat(e: SubmitEvent) {
 		e.preventDefault();
 		busy = true;
@@ -137,6 +183,9 @@
 			{#if !watching}
 				<button type="button" class="quiet" title="A phrase that brings this seat to another device" onclick={transfer}>Transfer seat</button>
 			{/if}
+			{#if room.isHost && room.started}
+				<button type="button" class="quiet" title="Bring a player back to a seat their browser lost, or give a seat to a housecarl" onclick={() => (seatsOpen = true)}>Seats</button>
+			{/if}
 		{/if}
 		<button type="button" class="quiet" onclick={() => (prefsOpen = true)}>Preferences</button>
 		<a class="quiet" href={room ? `/guide?room=${roomId}` : '/guide'}>How to play</a>
@@ -151,6 +200,7 @@
 <Preferences bind:open={prefsOpen} />
 {#if room}
 	<ReportSlip {room} bind:open={reporting} />
+	{#if room.isHost}<SeatsSlip {room} bind:open={seatsOpen} />{/if}
 {/if}
 
 {#if error}
@@ -189,8 +239,19 @@
 	</section>
 {/if}
 
+{#if room?.started && !seatLost && room.view.seats.some((s) => s.standIn)}
+	<p class="notice muted">A housecarl plays for {room.view.seats.filter((s) => s.standIn).map((s) => s.name).join(', ')}, at the host's word, until a transfer phrase from the host brings them back.</p>
+{/if}
+
 {#if watching && room?.started && !room.view.over}
-	<p class="notice muted">Had a seat at this table on another device? Transfer it from there and claim the phrase in the hall, or <a href="mailto:eric@ericwagoner.com?subject={encodeURIComponent(`My seat in room ${roomId}`)}">write to the keeper</a> for a link that brings it back.</p>
+	<div class="notice muted">
+		{#if seatLost}<p>{seatLost} Claim it here, or <a href="mailto:eric@ericwagoner.com?subject={encodeURIComponent(`My seat in room ${roomId}`)}">write to the keeper</a>.</p>
+		{:else}<p>Had a seat at this table? Ask the host for a transfer phrase, or make one on the device that still holds the seat, and claim it here. Or <a href="mailto:eric@ericwagoner.com?subject={encodeURIComponent(`My seat in room ${roomId}`)}">write to the keeper</a> for a link that brings it back.</p>{/if}
+		<form class="sit" onsubmit={claim}>
+			<input type="text" bind:value={claimPhrase} placeholder="the four-word phrase" autocomplete="off" aria-label="transfer phrase" />
+			<button type="submit" class="quiet" disabled={claiming || claimPhrase.trim().split(/[\s-]+/).length < 4}>Claim the seat</button>
+		</form>
+	</div>
 {/if}
 
 {#if room && !room.started}