So, I figured out my case, I hope this helps anyone else with the same issue
for some forsaken reason I had
# intelworkaround
export MESA_LOADER_DRIVER_OVERRIDE=i965
in my ~/.profile, which forced mesa to look for i965, failing since it has been
removed in testing, and falling back to SW rendering. you can check if you have
the same issue by using MESA_LOADER_DRIVER_OVERRIDE=iris (if iris is the one
corresponding to your intel graphics):
:~$ xdriinfo
libGL error: MESA-LOADER: failed to open i965: /usr/lib/dri/i965_dri.so: cannot
open shared object file: No such file or directory (search paths
/usr/lib/x86_64-linux-gnu/dri:\$${ORIGIN}/dri:/usr/lib/dri, suffix _dri)
libGL error: failed to load driver: i965
Screen 0: swrast
:~$ MESA_LOADER_DRIVER_OVERRIDE=iris xdriinfoScreen 0: iris
now HW acceleration is back and my sanity has been restored.
there should be a way of tracking insidious workarounds like that. one day
something breaks, you slap a quick workaround to have a working computer, but
the non-standard config stays there to bite you in the rear months/years later
