Jekyll _site directory persistence limits

Jekyll generates a static site by processing source files and Liquid templates into a destination directory, typically _site. This directory serves as the final production-ready output of the build pipeline.

Because the build process is designed to reflect the current state of the source files and _config.yml settings, the destination folder is treated as ephemeral. This creates a specific constraint when managing assets that may be generated by external scripts or manual modifications outside the standard Jekyll build cycle.

Given that the regeneration process typically involves recreating the destination folder from the source state, what are the documented limits for preserving specific files within the _site directory across multiple builds? Is there a native configuration to exclude specific sub-directories in the output folder from being overwritten during the build process?