A table's options and its size are read one way, in spec.ts, by the server, the tally and the replay; a game may seat fewer for some options

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

template/src/lib/components/Hall.svelte

@@ -14,6 +14,7 @@
 	import type { Report, RoomView, Tally } from '$lib/net/view';
 	import type { State } from '$lib/game';
 	import { game } from '$lib/game';
+	import { tableSize } from '$lib/game/spec';
 
 	let name = $state(playerName());
 	let code = $state('');
@@ -219,7 +220,7 @@
 		{/if}
 		<button type="button" class="commit primary" disabled={!ready || busy} onclick={() => open(() => Room.createWithBot(name.trim(), options))}>Play now against the bot</button>
 		<div class="ways">
-			<button type="button" class="quiet" disabled={!ready || busy} onclick={() => open(() => Room.create(name.trim(), game.seatIds.length, options))}>Open a table</button>
+			<button type="button" class="quiet" disabled={!ready || busy} onclick={() => open(() => Room.create(name.trim(), tableSize(game, options), options))}>Open a table</button>
 			<form class="joinform" onsubmit={join}>
 				<span class="or">or join one</span>
 				<input type="text" class="code" bind:value={code} maxlength="4" placeholder="CODE" autocapitalize="characters" autocomplete="off" aria-label="room code" />

template/src/lib/game/spec.test.ts

@@ -0,0 +1,22 @@
+import { describe, expect, it } from 'vitest';
+import { cleanOptions, tableSize, type TableOption } from './spec';
+
+const options: TableOption[] = [
+	{ key: 'length', label: 'Length', choices: [{ value: 'short', label: 'Short' }, { value: 'long', label: 'Long' }], default: 'short' }
+];
+
+describe('table options', () => {
+	it('keeps only declared options and offered choices, the rest at their defaults', () => {
+		expect(cleanOptions({ options }, { length: 'long', colour: 'red' })).toEqual({ length: 'long' });
+		expect(cleanOptions({ options }, { length: 'endless' })).toEqual({ length: 'short' });
+		expect(cleanOptions({ options }, null)).toEqual({ length: 'short' });
+	});
+
+	it('seats as many as the options allow, never more than the seats there are', () => {
+		const seatIds = ['A', 'B', 'C', 'D'];
+		expect(tableSize({ seatIds, options })).toBe(4);
+		const seatsFor = (o: Record<string, string>) => (o.length === 'short' ? 2 : 9);
+		expect(tableSize({ seatIds, options, seatsFor }, { length: 'short' })).toBe(2);
+		expect(tableSize({ seatIds, options, seatsFor }, { length: 'long' })).toBe(4);
+	});
+});

template/src/lib/game/spec.ts

@@ -48,6 +48,8 @@ export interface Preference {
 export interface GameSpec<State, Input> {
 	/** Seats in table order; the table takes at most this many. */
 	seatIds: SeatId[];
+	/** The most seats a table with these options takes, when an option makes it fewer than `seatIds`. */
+	seatsFor?(options: TableOptions): number;
 	/** What the host may choose when opening a table; empty for a game with one way to play. */
 	options?: TableOption[];
 	/** The game's own settings for the preferences panel. */
@@ -83,3 +85,24 @@ export interface GameSpec<State, Input> {
 	/** The game's own lines for the hall's tally, counted from a finished game: a label and how many it adds. */
 	tally?(state: State): Record<string, number>;
 }
+
+/**
+ * A table's options as the game will play them: only the options it
+ * declares, only the choices it offers, the rest at their defaults. The
+ * server, the tally and the ledger replay all read a room line through this,
+ * so each creates the same game from the same ledger.
+ */
+export function cleanOptions(game: Pick<GameSpec<unknown, unknown>, 'options'>, raw: unknown): TableOptions {
+	const given = (typeof raw === 'object' && raw !== null ? raw : {}) as Record<string, unknown>;
+	const options: TableOptions = {};
+	for (const o of game.options ?? []) {
+		const v = given[o.key];
+		options[o.key] = typeof v === 'string' && o.choices.some((c) => c.value === v) ? v : o.default;
+	}
+	return options;
+}
+
+/** The most seats a table with these options takes. */
+export function tableSize(game: Pick<GameSpec<unknown, unknown>, 'options' | 'seatIds' | 'seatsFor'>, raw?: unknown): number {
+	return Math.min(game.seatIds.length, game.seatsFor?.(cleanOptions(game, raw)) ?? game.seatIds.length);
+}