On Linux and macOS openUrl/openFolder spawned xdg-open/open and waited
for it on the UI thread: 50-300 ms per click where the opener forks and
exits, and on generic xdg-open sessions (sway, i3, WSLg, ...), which run
the browser or file manager as xdg-open's foreground child, the window
froze until the user closed that app. The opener is now left running
and a detached thread reaps it; the click returns at once.
Its stdin, stdout and stderr go to /dev/null again. That redirect was
lost in the switch to posix_spawnp, so a text-mode browser fallback
could take over the wallet's terminal.
The result now means "launched" rather than "exited 0" (no caller reads
it), and a non-zero opener exit is reported on stderr instead of in the
debug log. Windows (ShellExecute, which never waited) is unchanged.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>