Robert Green wrote:
I noticed a small spot of water on the basement floor this morning and
looked up to see a tiny pinhole leak in the copper pipe (tube?)
directly above. It leaks a droplet every few hours, so it's
something that a rag is absorbing for now.

What's the best way to repair it? It's near a joist hanger strap and
I suspect the damage was causing by an errant hammer blow and not
inherent vice. But that's just a guess. For all I know, pinholes
are about to emerge throughout the house.

This is the first pinhole leak I've ever seen in the house. Every
other leak (and in a 70 year old house there have been a few) has
been at copper/iron union, a coupling or a valve.

Just cut the pipe at the leak, and solder a coupling onto the 2 ends.