StdIn should be available()

[nipafx]

When reading from System.in, some extra code is needed to avoid blocking on empty input:

// prevent blocking
if (System.in.available() == 0)
	return new byte[0];
// input available ~> read
var reader = new BufferedReader(new InputStreamReader(System.in));
var input = reader.lines().collect(joining("\n"));

The standard I/O extension replaces System.in with StdIn, a subclass of InputStream that forwards read calls to a StringReader. But it doesn't forward or otherwise override other methods and so available() is called on InputStream, which returns 0. That means the blocking-prevention code above always leads to an empty array.

A fix would override available() (and potentially similar methods) but as far as I can see, it can't be forwarded to the underlying StringReader and so would require some unfortunate byte counting.