A 30 GiB disk (23 GiB free) failed install: pool = 90% of free = 20.7
GiB, leaving 2.3 GiB — under the 3 GiB reserve, so 10-incus.sh died
with "too little free space". Any disk with < 30 GiB free was
uninstallable.
Now the pool is shrunk in 512 MiB steps (down to a 1 GiB floor) until
the 3 GiB host reserve holds, instead of aborting. A small pool beats
no pool. Verified on the 30 GiB Ubuntu 24.04 test host: 19.5 GiB pool
created, install completes, full test suite passes.
Co-authored-by: CommandCodeBot <noreply@commandcode.ai>