A duel server: rooms, seat tokens, ledgers, and resolution when all have moved

Plain HTTP for actions and a websocket that only says "fetch again". A
room is its append-only ledger replayed from the top; the engine is
deterministic given the seed and the recorded inputs. Each seat sees a
view filtered to what the rules let it know. Bot seats are filled at
resolution time.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

server/src/store.ts

@@ -0,0 +1,42 @@
+// One append-only JSONL file per room. A room is its ledger replayed from the
+// top: the engine is deterministic given the seed and the recorded inputs, so
+// nothing else needs saving.
+
+import { appendFileSync, existsSync, mkdirSync, readFileSync, readdirSync } from 'node:fs';
+import { join } from 'node:path';
+import type { TurnInput, WizardId } from '../../src/lib/game/state';
+
+export type LedgerLine =
+	| { t: 'room'; id: string; seats: number; createdAt: number }
+	| { t: 'seat'; id: WizardId; name: string; token: string; bot: boolean }
+	| { t: 'start'; seed: number }
+	| { t: 'turn'; at: number; inputs: Record<WizardId, TurnInput> };
+
+export class Store {
+	constructor(private dir: string) {
+		mkdirSync(dir, { recursive: true });
+	}
+
+	private path(roomId: string): string {
+		return join(this.dir, `${roomId}.jsonl`);
+	}
+
+	append(roomId: string, line: LedgerLine): void {
+		appendFileSync(this.path(roomId), JSON.stringify(line) + '\n');
+	}
+
+	read(roomId: string): LedgerLine[] {
+		const path = this.path(roomId);
+		if (!existsSync(path)) return [];
+		return readFileSync(path, 'utf8')
+			.split('\n')
+			.filter((l) => l.trim())
+			.map((l) => JSON.parse(l) as LedgerLine);
+	}
+
+	roomIds(): string[] {
+		return readdirSync(this.dir)
+			.filter((f) => f.endsWith('.jsonl'))
+			.map((f) => f.slice(0, -'.jsonl'.length));
+	}
+}