type PhoneNumber = string & { __brand: "PhoneNumber" };

function parsePhone(input: string): PhoneNumber {
  if (!/^\+?\d{10,15}$/.test(input)) throw new Error(`Invalid: ${input}`);
  return input as PhoneNumber;
}

function sendSMS(to: PhoneNumber, body: string) {
  /* input is trusted */
}

// Don't — invalid combos representable
type State = { loading: boolean; user?: User; error?: string };

// Do — only valid states exist
type State =
  | { status: "loading" }
  | { status: "success"; user: User }
  | { status: "error"; error: string };

// Don't — duplicate shape, drifts when the row changes
type UserSummary = { id: string; email: Email };
function renderUser(u: UserSummary) {
  /* ... */
}

// Do — derive from the source of truth
type User = Awaited<ReturnType<typeof db.query.users.findFirst>>;
function renderUser(u: Pick<User, "id" | "email">) {
  /* ... */
}

// Don't — swap two args, still compiles
sendEmail("Welcome!", "Hi there");
// Do — order-independent, self-documenting
sendEmail({ to: "alice@x.com", body: "Hi there" });