Rehashes every page the host's GamendWeb.Sitemap.Source reports and moves
the <lastmod> date only for those whose content actually changed.
mix gamend.sitemap.lastmod # rewrite the manifest
mix gamend.sitemap.lastmod --check # fail if it is stale
mix gamend.sitemap.lastmod --dry-run # report changes, write nothing
mix gamend.sitemap.lastmod --notify # rewrite, then tell IndexNowRun it whenever content lands — after a translation sync, before a deploy — and commit the result. The manifest is data, not a build artifact: it is the only record of when a page reached its current state, so regenerating it from scratch on a fresh checkout would lose every date. Do not gitignore it.
--check belongs in CI next to mix gamend.settings.env_example --check: it
fails when content was edited without restamping, which is the mistake that
leaves the sitemap advertising dates that no longer match the pages.
The list of changed keys is printed so it can be fed to a change notifier —
see GamendWeb.IndexNow.