Speed up CI container builds

Run bootstrap inside existing bits-ci container to avoid devenv setup
overhead. Push full closure to Attic cache so intermediate derivations
are available for future builds. Tag images as :latest for subsequent
bootstrap runs to pull.

Author: jcf

.forgejo/workflows/bootstrap.yml

@@ -19,6 +19,11 @@ jobs:
   build:
     name: Build
     runs-on: nixos
+    container:
+      image: git.lan.invetica.co.uk/jcf/bits-ci:latest
+      credentials:
+        username: jcf
+        password: ${{ github.token }}
 
     steps:
       - uses: actions/checkout@v4
@@ -35,14 +40,23 @@ jobs:
           image_path=$(.forgejo/scripts/build.sh bits-ci-amd64 2>&1 | .forgejo/scripts/filter-devenv.sh | head -1)
           echo "image_path=$image_path" >> "$GITHUB_OUTPUT"
 
-      - name: Push to Attic cache
-        run: attic push invetica:invetica "${{ steps.build.outputs.image_path }}"
+      - name: Push closure to Attic cache
+        run: nix-store -qR "${{ steps.build.outputs.image_path }}" | xargs attic push invetica:invetica
 
       - name: Push to Forgejo
         run: |
           version="$(date +%Y%m%d)-$(git rev-parse --short HEAD)"
+          image="git.lan.invetica.co.uk/jcf/bits-ci"
           skopeo copy \
             "docker-archive:${{ steps.build.outputs.image_path }}" \
-            "docker://git.lan.invetica.co.uk/jcf/bits-ci:$version" \
+            "docker://$image:$version" \
             --dest-creds="jcf:${{ github.token }}"
-          echo "Pushed git.lan.invetica.co.uk/jcf/bits-ci:$version"
+          skopeo copy \
+            "docker-archive:${{ steps.build.outputs.image_path }}" \
+            "docker://$image:latest" \
+            --dest-creds="jcf:${{ github.token }}"
+          echo ""
+          echo "✨ Images pushed!"
+          echo ""
+          echo "$image:$version"
+          echo "$image:latest"