Thanks for all the replies, I have solved the problem. When making my initial configuration before running, I made the following typo:
maximum_object_size 32768 MB
Oops. (I meant KB, not MB!) Apparently, this causes squid to not cache anything. Not sure why. Perhaps there should be some range checking or validation on this configuration field.
After changing it to KB, all is well.
TIA,
Tom
