The open chat thread called std::localtime at least twice per message
per frame (two day keys for grouping), and more for day separators and
time labels. On glibc every call re-checks the timezone with a stat of
/etc/localtime. The chat time helpers now use util::localTime() from
the new util/local_time.h: localtime_r (localtime_s on Windows), with
no per-call timezone check and no shared static result buffer.
glibc's localtime_r reads the timezone only once, so local_time.h also
adds util::refreshTimezone() (tzset) for caches to call when they
rebuild. Nothing calls it yet; its first caller is the chat thread's
grouping-flags cache in the next commit.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
DanSandClaude Opus 5.5
a69380817e