There’s a wealth of reading available to you if you look up “trunk-based development” as a keyword. Likewise with “continuous integration” (the actual practice, not the build tooling). Jez Humble for instance has written extensively on this.
I know about this but haven't found an answer to my question. This was in part my motivation to post this question here.
You develop features behind compile or runtime flags and keep it off until it's ready to ship. This is what chromium.org does so that might be a more accessible way to see it in practice.
Yhere are a bunch of ways to land code that doesn’t get run yet, by adding new functions or default parameters and conditional logic.