Toxe
And 'hey Presto..!', all the files are back, the Project can be launched and run again..! Crisis over, and a lesson learned. At no point, in any of the docs I've consulted, is there any mention of the files 'going away'. Yes, it would appear that they were safe, but I don't see how I could continue work on the Project if the files are not where I expect them to be. This 'Checkout' has returned all, at the (small...) price of forcing Godot to re-import everything (maybe not a Bad Thing itself, but just extra time spent loading it into Godot...).
Many thanks, obviously, for having worked out how to rectify the situation. I'll have to do quite a lot more experimenting with GIT, on even smaller 'Test' Projects, until I'm confident that it's doing the job I want it to do, under my mastery. Meanwhile, I'll continue my Project 'zipping' for back-up.
Thanks again, and (of course...) Happy New Year (to all...).