The deploy never removes a deleted file from gh-pages (keep_files: true) #28

publish.yml deploys with peaceiris/actions-gh-pages@v4 and keep_files: true, so that a push to main does not wipe the live pr-N preview folders. The side effect is that the deploy never removes anything from gh-pages: a file deleted from the source stays on the site.

This has already happened once. #11 deleted six dataset files from lectures/_static on 2026-09-01. Three deploys later they were still served, byte-identical to the deleted files, and #27 had to remove them from gh-pages by hand on 2026-09-29. About 194 figure PNGs that were orphaned the same way are still on the branch.

One structural fix is for the deploy job to check out gh-pages, run rsync -a --delete --exclude 'pr-*/' of the build output over it, and push. Deleted files then go, and the previews stay. Alternatively, keep keep_files and add a cleanup step that can tell a preview folder from a stale file.

This is not urgent, because nothing reads the orphans today. It will bite again the next time a lecture or an asset is deleted.

Found during the datasets-migration close-out (QuantEcon/workspace-lectures#40).