Beginner: infer context type

export type Ctx = { Variables: { session: Session | null } };

export const app = new Hono<Ctx>()
  .use(async (c, n) => {
    const token = getCookie(c, "session") ?? "";

    const session = await validateSession(token);

    c.set("session", session);

    await n();
  })
  .post(
    "/sign-out",
    async (c, n) => {
      if (!c.var.session) {
        throw new HTTPException(401, { message: "unauthorized" });
      }

      await n();
    },
    async (c) => {
      c.var.session; // currently Session | null but it should be Session
    },
  );