Checked errors

Use throws to tell callers which failures they need to handle. Anyone calling loadUser must catch UserNotFound and StorageFailure, or declare them on their own function so its caller can handle them:

function loadUser(string $id): string
    throws UserNotFound, StorageFailure

The caller in the editor handles UserNotFound but forgets StorageFailure. Press Check to see the compiler catch it, then add the missing catch block after the first one:

} catch (StorageFailure $error) {
    echo 'unavailable';
}

Check again and the file passes. Press Run to print maya, then try an empty ID to see the UserNotFound catch print guest. These are ordinary PHP exceptions; throws helps you catch a forgotten handler before the program runs.