The guest passes and expects UTF-8 names, but on Windows opendir and
readdir used MinGW's narrow dirent API, which works in the ANSI code
page: opendir failed for a directory whose name is outside the code page,
and readdir returned names as ANSI bytes, with "?" for characters the code
page lacks. Use _wopendir and _wreaddir there and convert each name to
UTF-8.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>