diff --git a/docker-build-nix/README.md b/docker-build-nix/README.md
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+# docker-build-nix
+
+Build and push Docker/OCI images generated by Nix flakes, with Attic cache integration.
+
+## Features
+
+- **Reproducible builds**: Uses Nix flakes for bit-for-bit identical images
+- **Attic caching**: Pushes build artifacts to your Attic cache for faster subsequent builds
+- **Nix store optimization**: Leverages Nix's existing binary caches (nixos.org + your Attic)
+- **Smaller images**: Nix `dockerTools.buildLayeredImage` creates optimized layers
+
+## Usage
+
+### Basic example
+
+```yaml
+name: Build Docker Image
+on:
+  push:
+    branches: [main]
+
+jobs:
+  build:
+    runs-on: nix  # Requires runner with Nix
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: https://git.toph.so/toph/ci-actions/docker-build-nix@main
+        with:
+          flake-output: .#dojo-image
+          image-name: toph/dojo
+          registry-password: ${{ secrets.GITEA_TOKEN }}
+        env:
+          ATTIC_TOKEN: ${{ secrets.ATTIC_TOKEN }}
+```
+
+### Multiple images
+
+```yaml
+jobs:
+  build-web:
+    runs-on: nix
+    steps:
+      - uses: actions/checkout@v4
+      - uses: https://git.toph.so/toph/ci-actions/docker-build-nix@main
+        with:
+          flake-output: .#dojo-image
+          image-name: toph/dojo
+          image-tag: main
+          registry-password: ${{ secrets.GITEA_TOKEN }}
+        env:
+          ATTIC_TOKEN: ${{ secrets.ATTIC_TOKEN }}
+
+  build-agent:
+    runs-on: nix
+    steps:
+      - uses: actions/checkout@v4
+      - uses: https://git.toph.so/toph/ci-actions/docker-build-nix@main
+        with:
+          flake-output: .#agent-image
+          image-name: toph/dojo/agent
+          image-tag: main
+          registry-password: ${{ secrets.GITEA_TOKEN }}
+        env:
+          ATTIC_TOKEN: ${{ secrets.ATTIC_TOKEN }}
+```
+
+## Inputs
+
+| Input | Required | Default | Description |
+|-------|----------|---------|-------------|
+| `flake-output` | ✅ | - | Nix flake output (e.g., `.#dojo-image`) |
+| `image-name` | ✅ | - | Target image name (e.g., `user/repo`) |
+| `registry-password` | ✅ | - | Registry password/token |
+| `image-tag` | ❌ | `main` | Image tag |
+| `registry` | ❌ | `git.toph.so` | Docker registry |
+| `registry-username` | ❌ | `${{ gitea.actor }}` | Registry username |
+| `cache-name` | ❌ | `ci` | Attic cache name |
+| `attic-endpoint` | ❌ | `https://cache.toph.so` | Attic endpoint |
+
+## Environment Variables
+
+| Variable | Required | Description |
+|----------|----------|-------------|
+| `ATTIC_TOKEN` | Optional | Attic token for pushing to cache. If not set, skips cache push. |
+
+## How It Works
+
+1. **Build with Nix**: Runs `nix build <flake-output>` which uses Nix caching
+2. **Push to Attic**: Uploads the entire build closure to your Attic cache
+3. **Load to Docker**: Loads the OCI tarball into local Docker daemon
+4. **Tag & Push**: Tags and pushes to your Docker registry
+
+## Example Flake
+
+Your `flake.nix` should export image outputs:
+
+```nix
+{
+  outputs = { self, nixpkgs }:
+    let
+      pkgs = import nixpkgs { system = "x86_64-linux"; };
+    in
+    {
+      packages.x86_64-linux = {
+        # Your app
+        default = pkgs.callPackage ./package.nix { };
+
+        # OCI image
+        dojo-image = pkgs.dockerTools.buildLayeredImage {
+          name = "dojo";
+          tag = "latest";
+          contents = [ self.packages.x86_64-linux.default ];
+          config = {
+            Cmd = [ "${self.packages.x86_64-linux.default}/bin/dojo" ];
+          };
+        };
+      };
+    };
+}
+```
+
+## Prerequisites
+
+- **Nix runner**: Runner with `nix` label using `docker://registry.toph.so/nix-runner:latest`
+- **Attic cache**: Optional but recommended for caching (`cache.toph.so`)
+- **ATTIC_TOKEN**: Set in Forgejo secrets if you want cache push
+- **GITEA_TOKEN**: Auto-available in Forgejo Actions
+
+## Comparison with docker-build
+
+| Feature | docker-build | docker-build-nix |
+|---------|-------------|------------------|
+| Build method | Docker | Nix |
+| Reproducibility | Layer-dependent | Byte-for-byte |
+| Caching | S3 layers | Attic derivations |
+| Image size | Larger | Optimized |
+| Runner | Any | Requires Nix |
+
+## See Also
+
+- [docker-build](../docker-build/) - Traditional Docker builds with S3 cache
+- [push-nix-cache](../push-nix-cache/) - Push arbitrary Nix paths to Attic
diff --git a/docker-build-nix/action.yaml b/docker-build-nix/action.yaml
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+name: Build and Push Docker Image from Nix
+description: Build OCI image with Nix flake, push to registry with Attic caching
+
+inputs:
+  flake-output:
+    description: 'Nix flake output for the OCI image (e.g., .#dojo-image)'
+    required: true
+
+  image-name:
+    description: 'Target image name in registry (e.g., git.toph.so/user/repo)'
+    required: true
+
+  image-tag:
+    description: 'Image tag'
+    required: false
+    default: 'main'
+
+  registry:
+    description: 'Docker registry'
+    required: false
+    default: 'git.toph.so'
+
+  registry-username:
+    description: 'Registry username'
+    required: false
+    default: ${{ gitea.actor }}
+
+  registry-password:
+    description: 'Registry password/token'
+    required: true
+
+  cache-name:
+    description: 'Attic cache name to push build artifacts'
+    required: false
+    default: 'ci'
+
+  attic-endpoint:
+    description: 'Attic cache endpoint'
+    required: false
+    default: 'https://cache.toph.so'
+
+runs:
+  using: composite
+  steps:
+    - name: Build OCI image with Nix
+      shell: bash
+      run: |
+        echo "Building ${{ inputs.flake-output }}..."
+        nix build "${{ inputs.flake-output }}" --print-build-logs
+
+    - name: Push build artifacts to Attic cache
+      shell: bash
+      if: env.ATTIC_TOKEN != ''
+      env:
+        ATTIC_TOKEN: ${{ env.ATTIC_TOKEN }}
+      run: |
+        # Configure attic client
+        mkdir -p ~/.config/attic
+        cat > ~/.config/attic/config.toml <<EOF
+        [servers.cache]
+        endpoint = "${{ inputs.attic-endpoint }}"
+        token = "${ATTIC_TOKEN}"
+        EOF
+
+        # Push entire closure to cache
+        attic push "${{ inputs.cache-name }}" ./result
+
+    - name: Load image into Docker
+      shell: bash
+      run: |
+        echo "Loading OCI image into Docker..."
+        docker load < ./result
+
+    - name: Tag and push to registry
+      shell: bash
+      run: |
+        # Extract image name from the loaded output
+        IMAGE_ID=$(docker images --format "{{.Repository}}:{{.Tag}}" | head -n1)
+        echo "Loaded image: $IMAGE_ID"
+
+        # Tag with target name
+        TARGET_IMAGE="${{ inputs.registry }}/${{ inputs.image-name }}:${{ inputs.image-tag }}"
+        echo "Tagging as: $TARGET_IMAGE"
+        docker tag "$IMAGE_ID" "$TARGET_IMAGE"
+
+        # Login and push
+        echo "${{ inputs.registry-password }}" | docker login ${{ inputs.registry }} -u ${{ inputs.registry-username }} --password-stdin
+        docker push "$TARGET_IMAGE"