diff --git a/web/src/sdk/room.test.ts b/web/src/sdk/room.test.ts
new file mode 100644
index 0000000..b724d08
--- /dev/null
+++ b/web/src/sdk/room.test.ts
@@ -0,0 +1,141 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+import { Room } from "./room";
+
+const transport = vi.hoisted(() => ({
+  create: vi.fn(),
+}));
+
+vi.mock("partysocket", () => ({
+  PartySocket: vi.fn(function createSocket(options: unknown) {
+    return transport.create(options);
+  }),
+}));
+
+/** Emits only explicit test events; never opens a network connection. */
+class FakeSocket extends EventTarget {
+  readyState = 0;
+  bufferedAmount: number | undefined = 0;
+  readonly sent: unknown[] = [];
+  readonly close = vi.fn(() => this.transition("close", 3));
+
+  send(raw: string): void {
+    this.sent.push(JSON.parse(raw));
+  }
+
+  transition(event: "open" | "close" | "error", state: number): void {
+    this.readyState = state;
+    this.dispatchEvent(new Event(event));
+  }
+}
+
+describe("Room connection lifecycle", () => {
+  let socket: FakeSocket;
+  let room: Room;
+
+  beforeEach(() => {
+    vi.useFakeTimers();
+    vi.stubGlobal("window", globalThis);
+    vi.stubGlobal("WebSocket", { OPEN: 1 });
+    vi.spyOn(performance, "now").mockReturnValue(100);
+    socket = new FakeSocket();
+    transport.create.mockReturnValue(socket);
+    room = new Room("wss://relay.invalid/", "BCDFGH");
+  });
+
+  afterEach(() => {
+    room.close();
+    expect(vi.getTimerCount()).toBe(0);
+    vi.useRealTimers();
+    vi.restoreAllMocks();
+    vi.unstubAllGlobals();
+    transport.create.mockReset();
+  });
+
+  it("joins the stable display room and pings immediately then every two seconds", () => {
+    expect(transport.create).toHaveBeenCalledWith({
+      host: "relay.invalid",
+      room: "BCDFGH",
+    });
+    expect(room.code).toBe("BCDFGH");
+    expect(room.connectionState).toBe("connecting");
+    expect(room.isOpen).toBe(false);
+    expect(socket.sent).toEqual([]);
+
+    const connected = vi.fn();
+    room.on("conn", connected);
+    socket.transition("open", 1);
+
+    expect(connected).toHaveBeenCalledWith("open");
+    expect(room.connectionState).toBe("open");
+    expect(room.isOpen).toBe(true);
+    expect(socket.sent).toEqual([
+      { v: 1, type: "join", role: "display" },
+      { v: 1, type: "ping", t: 100 },
+    ]);
+    vi.advanceTimersByTime(1999);
+    expect(socket.sent).toHaveLength(2);
+    vi.mocked(performance.now).mockReturnValue(2100);
+    vi.advanceTimersByTime(1);
+    expect(socket.sent.at(-1)).toEqual({ v: 1, type: "ping", t: 2100 });
+  });
+
+  it("stops on close and rejoins on reconnect with exactly one ping loop", () => {
+    const states: string[] = [];
+    const unsubscribe = room.on("conn", (state) => states.push(state));
+    socket.transition("open", 1);
+    socket.transition("close", 3);
+    expect(room.connectionState).toBe("closed");
+    expect(vi.getTimerCount()).toBe(0);
+    vi.advanceTimersByTime(6000);
+    expect(socket.sent).toHaveLength(2);
+
+    socket.transition("error", 0);
+    expect(room.connectionState).toBe("connecting");
+    socket.transition("open", 1);
+    // A repeated open event must replace the interval rather than duplicate it.
+    socket.transition("open", 1);
+    expect(vi.getTimerCount()).toBe(1);
+    expect(
+      socket.sent.filter((msg) => (msg as { type: string }).type === "join")
+    ).toHaveLength(3);
+    const beforeTick = socket.sent.length;
+    vi.advanceTimersByTime(2000);
+    expect(socket.sent).toHaveLength(beforeTick + 1);
+    expect(states).toEqual(["open", "closed", "connecting", "open", "open"]);
+    unsubscribe();
+    room.close();
+    expect(socket.close).toHaveBeenCalledOnce();
+    expect(states).toHaveLength(5);
+    expect(room.connectionState).toBe("closed");
+    vi.advanceTimersByTime(6000);
+    expect(socket.sent).toHaveLength(beforeTick + 1);
+  });
+
+  it("sends start and recording control only while open and exposes backpressure", () => {
+    const recording = {
+      v: 1,
+      type: "rec",
+      action: "arm",
+      sessionId: "fixture-session",
+      anchorMs: 100,
+    } as const;
+    room.start();
+    room.sendRec(recording);
+    expect(socket.sent).toEqual([]);
+    socket.bufferedAmount = undefined;
+    expect(room.bufferedAmount).toBe(0);
+
+    socket.transition("open", 1);
+    socket.bufferedAmount = 4096;
+    expect(room.bufferedAmount).toBe(4096);
+    room.start();
+    room.sendRec(recording);
+    expect(socket.sent.slice(2)).toEqual([{ v: 1, type: "start" }, recording]);
+    room.close();
+    expect(room.isOpen).toBe(false);
+    room.start();
+    room.sendRec(recording);
+    expect(socket.sent).toHaveLength(4);
+  });
+});