Noob Mistakes

List of things to watch out for as a newbie (noob):

Gem-based themes must be over-ridden, not over-written

In your quest to customise your site, you might edit the default theme in-place (in-situ). Not a good idea. Which is to say, don’t edit the files at the global Gem home location, typically /home/<user>/gems/gems/minima-2.5.2

I realised this when I tried to publish to the CDN.
The CDN will pull the Gem theme from the Web, and your overwrites will never make it.

You need to instead, override any gem files by:
a) copying the file into the identical locaiton in your site project
b) editing the copy as desired

If you buggered your default Gem theme in-situ, restore it to pristine condition with

$ gem pristine minima

Better checkin the lockfile

Tracking Gemfile.lock helps guarantee configuration parity between local testing environment and the CDN web runner.
Else you might run into issues when a new version of a Gem is released.

Also on the CDN, activate runtime resolution by changing the deployment parameters from jekyll build to standard Bundler execution bundle exec jekyll build