add cache for build

.github/actions/nix-devshell/action.yml

@@ -12,6 +12,14 @@ inputs:
       "Commands to run inside the devshell (executed with bash -lc)."
     required: false
     default: ""
+  cachix_cache:
+    description: "Optional Cachix cache name to use (e.g. myorg). Requires `cachix_auth` for private caches."
+    required: false
+    default: ""
+  cachix_auth:
+    description: "Optional Cachix auth token used to access private caches (pass via secrets)."
+    required: false
+    default: ""
 
 runs:
   using: "composite"
@@ -29,6 +37,27 @@ runs:
         fi
         nix --version
 
+    - name: (Optional) Configure Cachix binary cache
+      if: ${{ inputs.cachix_cache != '' }}
+      shell: bash
+      run: |
+        set -euo pipefail
+        # install cachix CLI if absent (via nix)
+        if ! command -v cachix >/dev/null 2>&1; then
+          if command -v nix >/dev/null 2>&1; then
+            nix profile install nixpkgs#cachix || true
+          else
+            echo "nix not available - cannot install cachix"
+            exit 1
+          fi
+        fi
+        # authenticate if auth token provided (for private caches)
+        if [ -n "${{ inputs.cachix_auth }}" ]; then
+          echo "${{ inputs.cachix_auth }}" | cachix authtoken - || true
+        fi
+        # use the provided cachix cache
+        cachix use "${{ inputs.cachix_cache }}" || true
+
     - name: Prebuild devshell
       if: ${{ inputs.prebuild == 'true' }}
       shell: bash

.github/workflows/android.yaml

@@ -14,10 +14,47 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v6
 
+      - name: Cache Nix store/cache
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cache/nix
+            ~/.nix-profile
+            ~/.local/share/nix
+          key: ${{ runner.os }}-nix-${{ hashFiles('flake.lock','flake.nix') }}
+          restore-keys: |
+            ${{ runner.os }}-nix-
+
+      - name: Cache Flutter Pub
+        uses: actions/cache@v4
+        with:
+          path: ~/.pub-cache
+          key: ${{ runner.os }}-pub-${{ hashFiles('pubspec.lock','pubspec.yaml') }}
+          restore-keys: |
+            ${{ runner.os }}-pub-
+
+      - name: Cache Gradle
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.gradle/caches
+            ~/.gradle/wrapper
+            android/.gradle
+          key: ${{ runner.os }}-gradle-${{ hashFiles('android/gradle.properties','android/gradle/wrapper/gradle-wrapper.properties') }}
+          restore-keys: |
+            ${{ runner.os }}-gradle-
+
       - name: Prepare Nix devshell
         uses: ./.github/actions/nix-devshell
         with:
           prebuild: "true"
+          cachix_cache: ${{ secrets.CACHIX_CACHE }}
+          cachix_auth: ${{ secrets.CACHIX_AUTH_TOKEN }}
+
+      - name: Restore Dart packages
+        uses: ./.github/actions/nix-devshell
+        with:
+          commands: flutter pub get
 
       - name: Collect Translation Files
         uses: ./.github/actions/nix-devshell