CI: reusable_build:

I think the || logic here is wrong. All packages are checked even if only a single package has changed in a (force) push. It would seem that any push event always triggers make package/check (if [ "${{ github.event_name }}" = "push" ])

      - name: Download and check packages
        if: inputs.build_all_modules == true || inputs.build_all_kmods == true || inputs.build_full == true
        shell: su buildbot -c "sh -e {0}"
        working-directory: openwrt
        run: |
          # With push events or check_packages_list set to 'all', check all packages
          if [ "${{ github.event_name }}" = "push" ] || [ "${{ inputs.check_packages_list }}" = "all" ]; then
            make package/download package/check FIXUP=1 -j$(nproc) BUILD_LOG=1 || ret=$? .github/workflows/scripts/show_build_failures.sh
          # With every other event check only changed packages (if provided)
          elif [ -n "${{ inputs.check_packages_list }}" ]; then
            for package in ${{ inputs.check_packages_list }}; do
              make package/$package/download package/$package/check FIXUP=1 -j$(nproc) BUILD_LOG=1 || ret=$? .github/workflows/scripts/show_build_failures.sh
            done
          fi

Also, if only checksums have changed in a Makefile, package/check FIXUP=1 seems to do nothing locally (to warrant a git add blah; git commit --amend ; git push --force).

Start with the reusable_build workflow step shown in the issue and the referenced .github/workflows/scripts/show_build_failures.sh script. Reproduce both a push with one changed package and a checksum-only Makefile change, using the shown make package/download package/check commands. Done means package checks follow the changed-package list when appropriate and checksum-only changes have defined check behavior.