fix(publish): free runner disk before build and retry docker push

Auto-tracking the newest Godot/Blender means most nightly runs now
build genuinely new multi-GB layers instead of hitting cache, and
nothing ever pruned old ones — the runner's disk fills up over
successive runs until a push fails. Prune before building, and retry
docker push a few times to ride out transient registry 500s.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitea/workflows/publish.yml

@@ -65,6 +65,15 @@ jobs:
         id: blender
         run: echo "url=$(./scripts/resolve-blender-url.sh)" >> "$GITHUB_OUTPUT"
 
+      # Now that this workflow tracks the newest Godot/Blender instead of one
+      # pinned version, most nightly runs build genuinely new multi-GB layers
+      # instead of hitting cache — nothing here ever pruned old ones, so the
+      # runner's disk fills up over successive runs until a push (a blob
+      # write) is what finally fails. Clear stale images/build cache first.
+      - name: Free up runner disk
+        if: steps.resolve.outputs.skip != 'true'
+        run: docker system prune -af --volumes
+
       - name: Build and push
         if: steps.resolve.outputs.skip != 'true'
         run: |
@@ -74,11 +83,26 @@ jobs:
             --build-arg GODOT_VERSION="$VERSION" \
             --build-arg BLENDER_URL="${{ steps.blender.outputs.url }}" \
             -t "${IMAGE}:${VERSION}" .
-          docker push "${IMAGE}:${VERSION}"
+
+          # Registry blob PUTs have been failing with transient 500s
+          # (unrelated to build correctness) — retry a few times before
+          # giving up.
+          push_with_retry() {
+            for attempt in 1 2 3; do
+              if docker push "$1"; then
+                return 0
+              fi
+              echo "::warning::docker push $1 failed (attempt $attempt/3), retrying..."
+              sleep $((attempt * 10))
+            done
+            return 1
+          }
+
+          push_with_retry "${IMAGE}:${VERSION}"
 
           if [ "${{ steps.resolve.outputs.update_latest }}" = "true" ]; then
             docker tag "${IMAGE}:${VERSION}" "${IMAGE}:latest"
-            docker push "${IMAGE}:latest"
+            push_with_retry "${IMAGE}:latest"
           fi
 
       # Gitea packages belong to the owner, not a repo, by default — pushing