A move names the round it was made for; a stale one is refused

The room counts rounds played and sends the count in its view; a page
sends it back with each move, and the server refuses a move whose count
is behind (a slow connection, a second click, a stale tab), or that has
no count at all (an old page, told to reload). Before, such a move was
taken as the move for the next round. Found in Dip's acceptance run.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Jm2auWk6RP71CjaAb4FMoG

server/src/index.ts

@@ -247,7 +247,7 @@ async function handle(req: IncomingMessage, res: ServerResponse): Promise<void>
 	}
 	if (action === 'turn') {
 		const token = typeof body.token === 'string' ? body.token : undefined;
-		rooms.submit(room, token, body.input);
+		rooms.submit(room, token, body.input, body.resolved);
 		const seat = rooms.seatOf(room, token);
 		return send(res, 200, rooms.view(room, seat.id));
 	}

server/src/rooms.ts

@@ -51,6 +51,8 @@ export interface Room {
 	/** Inputs received for the turn in progress, by seat. */
 	pending: Record<WizardId, TurnInput>;
 	chat: ChatLine[];
+	/** Turns played so far, time stops included; a move names the count it was made against. */
+	resolved: number;
 	/** Bumped on every change a client might want to see. */
 	seq: number;
 	updatedAt: number;
@@ -92,7 +94,7 @@ const TRANSFER_FAIL_LIMIT = 20;
 
 /** A table with nobody seated yet. */
 function blank(id: string, size: number, createdAt: number, rematchOf: string | null, expected: string[], seq = 0): Room {
-	return { id, size, createdAt, seats: [], galleryTalk: false, challenge: null, expected, rematch: null, rematchOf, state: null, pending: {}, chat: [], seq, updatedAt: createdAt };
+	return { id, size, createdAt, seats: [], galleryTalk: false, challenge: null, expected, rematch: null, rematchOf, state: null, pending: {}, chat: [], resolved: 0, seq, updatedAt: createdAt };
 }
 
 export function normalizeCode(raw: string): string {
@@ -315,11 +317,18 @@ export class Rooms {
 		this.commit(room, { t: 'unseat', id: seat.id });
 	}
 
-	/** Record a seat's move on the ledger, so a restart keeps it; resolve the turn once nobody else is awaited. */
-	submit(room: Room, token: string | undefined, raw: unknown): void {
+	/**
+	 * Record a seat's move on the ledger, so a restart keeps it; resolve the turn once nobody else is awaited.
+	 * `resolved` is how many turns the page had seen played when the gestures were made: gestures that
+	 * arrive after their turn was played (a slow connection, a second click, a stale tab) are refused
+	 * rather than taken as the next turn's.
+	 */
+	submit(room: Room, token: string | undefined, raw: unknown, resolved?: unknown): void {
 		const seat = this.seatOf(room, token);
 		if (!room.state) throw new RoomError('The duel has not begun: seats are still empty.', 409);
 		if (room.state.over) throw new RoomError('The duel is over.', 409);
+		if (typeof resolved !== 'number') throw new RoomError('This page is out of date. Reload it to see the duel as it stands.', 409);
+		if (resolved !== room.resolved) throw new RoomError('Those gestures were made for a turn that has already been played. Your page will catch up.', 409);
 		if (!waitingOn(room).includes(seat.id)) throw new RoomError('It is not your move.', 409);
 		this.commit(room, { t: 'input', at: Date.now(), id: seat.id, input: cleanInput(raw) });
 		if (waitingOn(room).length === 0) this.resolve(room);
@@ -356,6 +365,7 @@ export class Rooms {
 			host: room.seats[0]?.id ?? seatId,
 			seats: room.seats.map((s) => ({ id: s.id, name: s.name, bot: s.bot })),
 			waitingOn: waitingOn(room),
+			resolved: room.resolved,
 			state: room.state ? viewFor(room.state, seatId) : null,
 			chat: room.chat,
 			audience: this.gallery.get(room.id) ?? 0,
@@ -450,6 +460,7 @@ function apply(room: Room, line: LedgerLine): void {
 			if (!room.state) return;
 			room.state = resolveTurn(room.state, line.inputs);
 			room.pending = {};
+			room.resolved += 1;
 			break;
 		case 'over':
 			break;