Thank you for this series, Luke. I am learning a lot! There were a few nitpicks and random thoughts I thought I'd poke in here, just because :).

"CI" isn't automation as much as a practice of integrating various of branches of development together as frequently as possible ("continuously"). You could, theoretically, have CI (frequent integration with manual verification) without a pipeline, and a pipeline without CI (running it on long-lived branches). Automation helps make this practice less painful/safe and more viable.

a software development practice where members of a team integrate their work frequently... usually each person integrates at least once a day — leading to multiple integrations per day. Each integration is verified by an automated build (including test) to detect integration errors as quickly as possible.

@7 is equivalent to ^7.0.0 in composer/npm I believe. So authors will manually move those tags to the latest of the 7.x.x branch and that's how you ask for whatever's latest in that branch.

We've had issues with ubuntu-latest. Better to pin to a specific version to make upgrading to newer (especially major) versions of the OS more deliberate.

No Plans to Merge