Harden GitHub Pages demo deployment for stable latest-build links

[Copilot]

The README badge points to a stable demo/build/latest/ URL, but the Pages deployment was still fragile: the workflow published the SHA build and latest redirect in separate pushes, which could leave latest/ stale or missing and surface as a 404. This change makes the Pages publish atomic and adds retention controls for accumulated demo artifacts.

• Atomic Pages publish

  • Stage both outputs into one deploy tree:
    • demo/build/<short-sha>/index.html
    • demo/build/<short-sha>/hra.jsdos
    • demo/build/latest/index.html
  • Replace the two sequential peaceiris/actions-gh-pages publishes with a single publish to demo/build

• Stable latest-path verification

  • Add post-deploy smoke checks for:
    • https://luke-b.github.io/DosTest/demo/build/<short-sha>/
    • https://luke-b.github.io/DosTest/demo/build/latest/
  • Keep retries short so transient propagation delays are tolerated without materially slowing the workflow

• gh-pages retention / pruning

  • Check out gh-pages in the workflow and keep only the newest retained SHA build directories
  • Exclude latest/ from pruning
  • Guard the retain-count input and only commit/push when pruning actually changes the branch

• Workflow cleanup

  • Remove the old split-deploy path and its exclude_assets dependency
  • Make prune-step failure modes explicit so bad branch state surfaces as a workflow error instead of silently skewing retention

- name: Stage demo deployment
  run: |
    SHORT_SHA="${{ steps.sha.outputs.short }}"
    mkdir -p "staging/demo/build/${SHORT_SHA}" "staging/demo/build/latest"
    cp index.html "staging/demo/build/${SHORT_SHA}/index.html"
    cp hra.jsdos "staging/demo/build/${SHORT_SHA}/hra.jsdos"
    cp latest-redirect/index.html "staging/demo/build/latest/index.html"

- name: Deploy demo to gh-pages
  uses: peaceiris/actions-gh-pages@v4
  with:
    github_token: ${{ secrets.GITHUB_TOKEN }}
    publish_dir: ./staging/demo/build
    destination_dir: demo/build
    keep_files: true

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