diff --git a/src/web/websocket-auth.test.ts b/src/web/websocket-auth.test.ts
new file mode 100644
index 0000000..efd9a9d
--- /dev/null
+++ b/src/web/websocket-auth.test.ts
@@ -0,0 +1,74 @@
+import { describe, it, expect, beforeEach, afterEach } from "vitest";
+import express from "express";
+import http from "node:http";
+import { WebSocketServer, WebSocket as WSClient } from "ws";
+import { AddressInfo } from "node:net";
+import { createDatabase, type BotDatabase } from "../data/database.js";
+import { createUserStore } from "../data/users.js";
+import { createSessionStore } from "../data/sessions.js";
+import { validateSessionFromHeaders, SESSION_COOKIE_NAME } from "./auth/validateSession.js";
+
+function buildServer(sessions: ReturnType<typeof createSessionStore>) {
+  const app = express();
+  const server = http.createServer(app);
+  const wss = new WebSocketServer({ noServer: true });
+  wss.on("connection", (ws) => ws.send("hello"));
+  server.on("upgrade", (req, socket, head) => {
+    if (req.url !== "/ws") return socket.destroy();
+    const r = validateSessionFromHeaders(req.headers.cookie as string | undefined, sessions);
+    if (!r) {
+      socket.write("HTTP/1.1 401 Unauthorized\r\nConnection: close\r\n\r\n");
+      socket.destroy();
+      return;
+    }
+    wss.handleUpgrade(req, socket, head, (ws) => wss.emit("connection", ws, req));
+  });
+  return { server, wss };
+}
+
+describe("WebSocket auth at upgrade", () => {
+  let botDb: BotDatabase;
+  let httpServer: http.Server;
+  let port: number;
+  let validToken: string;
+
+  beforeEach(async () => {
+    botDb = createDatabase(":memory:");
+    const users = createUserStore(botDb.db);
+    const sessions = createSessionStore(botDb.db);
+    const u = await users.createUser("alice", "pw");
+    validToken = sessions.createSession(u.id).token;
+
+    const { server } = buildServer(sessions);
+    httpServer = server;
+    await new Promise<void>((resolve) => httpServer.listen(0, resolve));
+    port = (httpServer.address() as AddressInfo).port;
+  });
+
+  afterEach(async () => {
+    await new Promise<void>((resolve) => httpServer.close(() => resolve()));
+    botDb.close();
+  });
+
+  it("rejects upgrade without cookie (server-side close before open)", async () => {
+    const ws = new WSClient(`ws://127.0.0.1:${port}/ws`);
+    const result = await new Promise<string>((resolve) => {
+      ws.on("open", () => resolve("opened"));
+      ws.on("unexpected-response", (_req, res) => resolve(`status:${res.statusCode}`));
+      ws.on("error", () => resolve("error"));
+    });
+    expect(result).toMatch(/^status:401$|^error$/);
+  });
+
+  it("accepts upgrade with a valid cookie", async () => {
+    const ws = new WSClient(`ws://127.0.0.1:${port}/ws`, {
+      headers: { Cookie: `${SESSION_COOKIE_NAME}=${validToken}` },
+    });
+    const msg = await new Promise<string>((resolve, reject) => {
+      ws.on("message", (data) => resolve(data.toString()));
+      ws.on("error", reject);
+    });
+    expect(msg).toBe("hello");
+    ws.close();
+  });
+});