Re: action=warn does not work on copy:

[Bob]

Thanks for the tip.  Adding that to the copy: instruction did the
trick.  It also caused me to stumble onto the inform setting in the
control: section, which will also be useful.

But that brings up another question:  How do you learn about these
things?  The reference manual does list the inform= option for copy:
and file:, but there's no description of what it does.  Do you just
have to try it and see?