🚀 go-pugleaf

Thanks for your answers, folks. You have confirmed what I suspected 
(but could not be sure).

Belt-and-braces - I synchronized the vector while I took a clone, then
enumerated the clone after releasing the sync-lock, and everything is 
fine now. 

I expected someome to ask if I intended other threads to be adding and
removing elements to a vector that I was enumerating. If you're 
interested, the answer is yes - the enumerating thread is just a 
periodic scan for unanswered requests that need retransmitting.
If it's just been added, it's not old enough to need resending, and
if it's being removed it has just been answered.

Thanks again.
Steve.