So? All the letters in this string are “just text”: "\u0000\u0089\uDEAD\uD9BF\uDFFF" JSON itself allows putting sequences of escape characters in the str

So? All the letters in this string are “just text”: "\u0000\u0089\uDEAD\uD9BF\uDFFF" JSON itself allows putting sequences of escape characters in the string that don’t unescape to valid Unicode. That’s fine, because the strings aren’t required to represent any particular encoding: it’s up to a layer higher than JSON to be opinionated about that. I wouldn’t want my shell’s pipeline buffers to reject data it doesn’t like, why should a JSON serializer?