ci: cache pub deps, filter jobs by path, and speed up release builds

CI (every push/PR):
- pub-cache cached keyed on pubspec.lock
- dorny/paths-filter skips the Flutter job for Go-only changes and
  vice versa (skipped required checks count as passing)

Release:
- gomobile installed from the go.mod-pinned x/mobile version instead
  of @latest (reproducible, covered by the setup-go cache; verified
  locally that go.sum already satisfies cmd/gomobile)
- Android bind targets arm/arm64/amd64 only - 386 dropped, amd64 kept
  so the universal APK still runs on x86_64 emulators
- NDK r29 cached; docker prune dropped from the free-space step
- Flutter pinned to 3.41.5 (matches .fvmrc/ci.yml) in both build jobs
  plus pub-cache caching; xcodeproj gem installed only when missing

.github/workflows/ci.yml

@@ -11,9 +11,41 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
+  changes:
+    name: Detect changed paths
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: read
+    outputs:
+      dart: ${{ steps.filter.outputs.dart }}
+      go: ${{ steps.filter.outputs.go }}
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v6
+
+      - name: Filter paths
+        uses: dorny/paths-filter@v3
+        id: filter
+        with:
+          filters: |
+            dart:
+              - 'lib/**'
+              - 'test/**'
+              - 'assets/**'
+              - 'pubspec.yaml'
+              - 'pubspec.lock'
+              - 'analysis_options.yaml'
+              - 'l10n.yaml'
+              - '.github/workflows/ci.yml'
+            go:
+              - 'go_backend/**'
+              - '.github/workflows/ci.yml'
+
   flutter:
     name: Flutter analyze & test
     runs-on: ubuntu-latest
+    needs: changes
+    if: needs.changes.outputs.dart == 'true'
 
     steps:
       - name: Checkout repository
@@ -27,6 +59,13 @@ jobs:
           channel: "stable"
           cache: true
 
+      - name: Cache pub dependencies
+        uses: actions/cache@v5
+        with:
+          path: ~/.pub-cache
+          key: pub-${{ runner.os }}-${{ hashFiles('pubspec.lock') }}
+          restore-keys: pub-${{ runner.os }}-
+
       - name: Get Flutter dependencies
         run: flutter pub get
 
@@ -39,6 +78,8 @@ jobs:
   go:
     name: Go vet & test
     runs-on: ubuntu-latest
+    needs: changes
+    if: needs.changes.outputs.go == 'true'
 
     defaults:
       run:

.github/workflows/release.yml

@@ -47,15 +47,14 @@ jobs:
     steps:
       - name: Free disk space
         run: |
-          # Remove large unused tools (~15GB total)
+          # Remove large unused tools (~15GB total). Docker prune was dropped:
+          # it took 1-2 minutes and the rm below already frees enough.
           sudo rm -rf /usr/share/dotnet
           sudo rm -rf /opt/ghc
           sudo rm -rf /opt/hostedtoolcache/CodeQL
           sudo rm -rf /usr/local/share/boost
           sudo rm -rf /usr/share/swift
           sudo rm -rf /usr/local/.ghcup
-          # Clean docker images
-          sudo docker image prune --all --force
           # Show available space
           df -h
 
@@ -84,6 +83,12 @@ jobs:
           key: gradle-${{ runner.os }}-${{ hashFiles('**/*.gradle*', '**/gradle-wrapper.properties') }}
           restore-keys: gradle-${{ runner.os }}-
 
+      - name: Cache Android NDK
+        uses: actions/cache@v5
+        with:
+          path: /usr/local/lib/android/sdk/ndk/29.0.14206865
+          key: ndk-29.0.14206865
+
       - name: Install Android SDK & NDK
         run: |
           # Use pre-installed Android SDK on GitHub runners
@@ -101,24 +106,38 @@ jobs:
           echo "ANDROID_NDK_HOME=$ANDROID_HOME/ndk/29.0.14206865" >> $GITHUB_ENV
 
       - name: Install gomobile
+        working-directory: go_backend
         run: |
-          go install golang.org/x/mobile/cmd/gomobile@latest
+          # Installed from inside the module so the go.mod-pinned x/mobile
+          # version is used (reproducible + covered by the setup-go cache).
+          go install golang.org/x/mobile/cmd/gomobile
           gomobile init
 
       - name: Build Go backend for Android
         working-directory: go_backend
         run: |
           mkdir -p ../android/app/libs
-          gomobile bind -target=android -androidapi 24 -o ../android/app/libs/gobackend.aar .
+          # arm/arm64 for shipped APKs, amd64 so the universal APK still works
+          # on x86_64 emulators; 386 devices no longer exist.
+          gomobile bind -target=android/arm,android/arm64,android/amd64 -androidapi 24 -o ../android/app/libs/gobackend.aar .
         env:
           CGO_ENABLED: 1
 
       - name: Setup Flutter
         uses: subosito/flutter-action@v2
         with:
+          # Keep in sync with .fvmrc and ci.yml
+          flutter-version: "3.41.5"
           channel: "stable"
           cache: true
 
+      - name: Cache pub dependencies
+        uses: actions/cache@v5
+        with:
+          path: ~/.pub-cache
+          key: pub-${{ runner.os }}-${{ hashFiles('pubspec.lock') }}
+          restore-keys: pub-${{ runner.os }}-
+
       - name: Get Flutter dependencies
         run: flutter pub get
 
@@ -191,8 +210,10 @@ jobs:
           restore-keys: pods-${{ runner.os }}-
 
       - name: Install gomobile
+        working-directory: go_backend
         run: |
-          go install golang.org/x/mobile/cmd/gomobile@latest
+          # go.mod-pinned x/mobile version (reproducible + cached by setup-go).
+          go install golang.org/x/mobile/cmd/gomobile
           gomobile init
 
       - name: Build Go backend for iOS
@@ -210,8 +231,9 @@ jobs:
 
       - name: Add XCFramework to Xcode project
         run: |
-          # Install xcodeproj gem for modifying Xcode project
-          sudo gem install xcodeproj
+          # xcodeproj usually ships with the preinstalled CocoaPods; only
+          # install it when missing.
+          gem list -i xcodeproj >/dev/null || sudo gem install xcodeproj
 
           # Create Ruby script to add framework
           cat > add_framework.rb << 'EOF'
@@ -251,9 +273,18 @@ jobs:
       - name: Setup Flutter
         uses: subosito/flutter-action@v2
         with:
+          # Keep in sync with .fvmrc and ci.yml
+          flutter-version: "3.41.5"
           channel: "stable"
           cache: true
 
+      - name: Cache pub dependencies
+        uses: actions/cache@v5
+        with:
+          path: ~/.pub-cache
+          key: pub-${{ runner.os }}-${{ hashFiles('pubspec.lock') }}
+          restore-keys: pub-${{ runner.os }}-
+
       - name: Get Flutter dependencies
         run: flutter pub get