Add bun:sqlite persistence layer

.gitignore

@@ -32,3 +32,5 @@ report.[0-9]_.[0-9]_.[0-9]_.[0-9]_.json
 
 # Finder (MacOS) folder config
 .DS_Store
+
+*.db

src/db.test.ts

@@ -0,0 +1,52 @@
+import { describe, it, expect, beforeEach, afterEach } from "bun:test";
+import { initDb, saveUpdate, getUpdates, close } from "./db";
+import { unlinkSync } from "fs";
+
+const TEST_DB = ":memory:";
+
+describe("db persistence", () => {
+	beforeEach(() => {
+		initDb(TEST_DB);
+	});
+
+	afterEach(() => {
+		close();
+	});
+
+	it("saves and retrieves updates for a room", () => {
+		const room = "test-room";
+		const update1 = new Uint8Array([1, 2, 3]);
+		const update2 = new Uint8Array([4, 5, 6]);
+
+		saveUpdate(room, update1);
+		saveUpdate(room, update2);
+
+		const updates = getUpdates(room);
+		expect(updates).toHaveLength(2);
+		expect(updates[0]).toEqual(update1);
+		expect(updates[1]).toEqual(update2);
+	});
+
+	it("returns empty array for unknown room", () => {
+		const updates = getUpdates("nonexistent");
+		expect(updates).toEqual([]);
+	});
+
+	it("rooms are isolated", () => {
+		const room1 = "room-one";
+		const room2 = "room-two";
+		const update1 = new Uint8Array([1, 1, 1]);
+		const update2 = new Uint8Array([2, 2, 2]);
+
+		saveUpdate(room1, update1);
+		saveUpdate(room2, update2);
+
+		const room1Updates = getUpdates(room1);
+		const room2Updates = getUpdates(room2);
+
+		expect(room1Updates).toHaveLength(1);
+		expect(room2Updates).toHaveLength(1);
+		expect(room1Updates[0]).toEqual(update1);
+		expect(room2Updates[0]).toEqual(update2);
+	});
+});

src/db.ts

@@ -0,0 +1,36 @@
+import { Database } from "bun:sqlite";
+
+let db: Database | null = null;
+
+export function initDb(path: string): void {
+	db = new Database(path);
+	db.exec(`
+		CREATE TABLE IF NOT EXISTS updates (
+			id INTEGER PRIMARY KEY AUTOINCREMENT,
+			room TEXT NOT NULL,
+			data BLOB NOT NULL,
+			created_at INTEGER DEFAULT (unixepoch())
+		);
+		CREATE INDEX IF NOT EXISTS idx_room ON updates(room);
+	`);
+}
+
+export function saveUpdate(room: string, data: Uint8Array): void {
+	if (!db) throw new Error("Database not initialized");
+	const stmt = db.prepare("INSERT INTO updates (room, data) VALUES (?, ?)");
+	stmt.run(room, data);
+}
+
+export function getUpdates(room: string): Uint8Array[] {
+	if (!db) throw new Error("Database not initialized");
+	const stmt = db.prepare("SELECT data FROM updates WHERE room = ? ORDER BY id ASC");
+	const rows = stmt.all(room) as Array<{ data: Uint8Array }>;
+	return rows.map(row => row.data);
+}
+
+export function close(): void {
+	if (db) {
+		db.close();
+		db = null;
+	}
+}