perf(docker): parallelize multi-arch build and improve layer caching

Split the single docker job into a matrix (amd64/arm64) that builds in
parallel, then merge via docker-manifest job. Also restructure the
Dockerfile to pre-compile dependencies with dummy sources so the dep
layer is cached by GHA when only application code changes.

.github/workflows/release.yml

@@ -108,7 +108,7 @@ jobs:
           args: --target ${{ matrix.target }}
 
   publish:
-    needs: [build, docker]
+    needs: [build, docker-manifest]
     runs-on: ubuntu-latest
     steps:
       - name: Publish draft release
@@ -318,6 +318,10 @@ jobs:
 
   docker:
     runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        platform: [linux/amd64, linux/arm64]
     steps:
       - uses: actions/checkout@v4
 
@@ -333,18 +337,58 @@ jobs:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
 
+      - name: Build and push by digest
+        id: build
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          platforms: ${{ matrix.platform }}
+          outputs: type=image,name=${{ secrets.DOCKERHUB_USERNAME }}/dbx,push-by-digest=true,name-canonical=true,push=true
+          cache-from: type=gha,scope=${{ matrix.platform }}
+          cache-to: type=gha,scope=${{ matrix.platform }},mode=max
+
+      - name: Export digest
+        run: |
+          mkdir -p /tmp/digests
+          digest="${{ steps.build.outputs.digest }}"
+          touch "/tmp/digests/${digest#sha256:}"
+
+      - name: Upload digest
+        uses: actions/upload-artifact@v4
+        with:
+          name: digests-${{ matrix.platform == 'linux/amd64' && 'amd64' || 'arm64' }}
+          path: /tmp/digests/*
+          if-no-files-found: error
+          retention-days: 1
+
+  docker-manifest:
+    needs: docker
+    runs-on: ubuntu-latest
+    steps:
+      - name: Download digests
+        uses: actions/download-artifact@v4
+        with:
+          path: /tmp/digests
+          pattern: digests-*
+          merge-multiple: true
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Login to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
       - name: Extract version from tag
         id: version
         run: echo "version=${GITHUB_REF_NAME#v}" >> "$GITHUB_OUTPUT"
 
-      - name: Build and push
-        uses: docker/build-push-action@v6
-        with:
-          context: .
-          platforms: linux/amd64,linux/arm64
-          push: true
-          tags: |
-            ${{ secrets.DOCKERHUB_USERNAME }}/dbx:${{ steps.version.outputs.version }}
-            ${{ secrets.DOCKERHUB_USERNAME }}/dbx:latest
-          cache-from: type=gha
-          cache-to: type=gha,mode=max
+      - name: Create manifest list and push
+        working-directory: /tmp/digests
+        run: |
+          docker buildx imagetools create \
+            -t ${{ secrets.DOCKERHUB_USERNAME }}/dbx:${{ steps.version.outputs.version }} \
+            -t ${{ secrets.DOCKERHUB_USERNAME }}/dbx:latest \
+            $(printf '${{ secrets.DOCKERHUB_USERNAME }}/dbx@sha256:%s ' *)

Dockerfile

@@ -23,17 +23,31 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     && rustup target add x86_64-unknown-linux-gnu aarch64-unknown-linux-gnu \
     && rm -rf /var/lib/apt/lists/*
 
+# Copy dependency manifests only and create dummy sources to pre-compile dependencies.
+# This layer is cached by GHA as long as Cargo.toml/Cargo.lock don't change.
 COPY Cargo.toml Cargo.lock ./
-COPY crates/ crates/
-COPY src-web/ src-web/
-RUN mkdir -p src-tauri/src && echo 'fn main() {}' > src-tauri/src/main.rs && echo 'pub fn run() {}' > src-tauri/src/lib.rs
+COPY crates/dbx-core/Cargo.toml crates/dbx-core/
+COPY src-web/Cargo.toml src-web/
 COPY src-tauri/Cargo.toml src-tauri/
+RUN mkdir -p crates/dbx-core/src && echo '' > crates/dbx-core/src/lib.rs \
+    && mkdir -p src-web/src && echo 'fn main() {}' > src-web/src/main.rs \
+    && mkdir -p src-tauri/src && echo 'fn main() {}' > src-tauri/src/main.rs && echo 'pub fn run() {}' > src-tauri/src/lib.rs
+
 COPY src-tauri/build.rs src-tauri/
 COPY src-tauri/tauri.conf.json src-tauri/
 
-RUN --mount=type=cache,target=/usr/local/cargo/registry,id=cargo-registry-$TARGETARCH \
-    --mount=type=cache,target=/app/target,id=cargo-target-$TARGETARCH \
-    case "$TARGETARCH" in \
+RUN case "$TARGETARCH" in \
+      amd64) rust_target=x86_64-unknown-linux-gnu ;; \
+      arm64) rust_target=aarch64-unknown-linux-gnu ;; \
+      *) echo "Unsupported TARGETARCH: $TARGETARCH" >&2; exit 1 ;; \
+    esac && \
+    cargo zigbuild --release -p dbx-web --target "$rust_target" || true
+
+# Copy real sources and rebuild (only application code recompiles)
+COPY crates/ crates/
+COPY src-web/ src-web/
+
+RUN case "$TARGETARCH" in \
       amd64) rust_target=x86_64-unknown-linux-gnu ;; \
       arm64) rust_target=aarch64-unknown-linux-gnu ;; \
       *) echo "Unsupported TARGETARCH: $TARGETARCH" >&2; exit 1 ;; \