gtkmm sets both the C and the C++ global locale from the environment, so
an unguarded stream writes "0,35" on a German desktop and groups 1920 as
"1.920" — neither of which the reader, or any other JSON reader, can take
back. Both the writer and the number parser now work in the classic
locale: the writer imbues its stream, and the parser uses from_chars
rather than stod, JSON having a point for a decimal mark whatever the
user's mark is.
The seed is read from the digits it was written as rather than from the
double they parsed into: a 64-bit seed has more bits than a double has
mantissa, and a seed that comes back off by a few is a project that no
longer renders its own picture.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
