Utf8OutputStream

An OutputStream that buffers incomplete UTF-8 byte sequences across writes, forwarding only complete characters as strings to the underlying RpcConsole.

This is needed because upstream byte sources (e.g. mill.constants.ProxyStream) may split writes at arbitrary byte boundaries, potentially in the middle of multi-byte UTF-8 characters. Without buffering, such partial sequences would be converted to the Unicode replacement character (U+FFFD).