It's all good now!I wrote that the model checksum from http://jenkins.trisquel.info/makeiso-etiona/iso/trisquel-mini_9.0_amd64.iso.sha256 is acae2029[…]b589d9f9", but (now, at least) it's 60c36600[…]9f6d140b, the same as my last download's checksum output.
Also I noticed my first ISO download was smaller than the other tries, so perhaps that is why installation failed.
I still don't understand it, but I hope it will work now.
