I'm at loss what to do to fix the issue: how does ECL have
early_signal_signal_error set as signal callback even before cl_boot was
Based on your platform specifications, this cannot happen. Signal handlers are installed only when cl_boot is launched -- this might not always be the same on other platforms, such as Windows, but on Debian/x86_64 it is.
Are you sure the signal does not happen _inside_ cl_boot()? Or because one thread is calling cl_boot() and another one is generating the signals?