A flat-file website is easy to move when its source, configuration, and media are easy to find. A fresh checkout is a good test. Can you figure out which files are meant to be edited and which are recreated by the build?

Separate content from build output

Keep Markdown posts, templates, site configuration, and the dependency lockfile with the source. Decide where the original images live, and check that a fresh build can find them. Keep machine-specific settings and credentials outside Git so the same checkout can be used in different environments.

Generated HTML and compiled assets have their own lifecycle. If a hosting service needs those files in a deployment branch, let the build write them there. Fix the Markdown, template, or stylesheet at its source so the next export carries the correction forward.

Try building from a clean checkout occasionally. A missing dependency or a file that exists only on your workstation is much easier to discover during a rehearsal than during a release.