Last night I had to run:
```
$ sudo apt update && sudo apt install resolvconf
```
So, I could sensibly connect to the Internet.
Obviously, that was because `resolvconf` somehow became uninstalled. That deduction came after a fair few hours flapping about. The only conclusion I can come to is that the last but one `$ sudo apt update && sudo apt upgrade` removed `resolvconf` ...
I'm more than happy to run any diagnostic stuff, but I'm unsure how to obtain a transaction history from `apt`