CI: add Android runner disk cleanup and space guards

.github/workflows/android-build.yml

@@ -37,7 +37,6 @@ jobs:
         with:
           distribution: temurin
           java-version: ${{ env.JAVA_VERSION }}
-          cache: gradle
 
       - name: Set up Flutter
         uses: subosito/flutter-action@v2
@@ -46,6 +45,39 @@ jobs:
           channel: stable
           cache: true
 
+      - name: Free runner disk space
+        shell: bash
+        run: |
+          set -euo pipefail
+          echo '--- Disk usage before cleanup ---'
+          df -h /
+          echo '--- Largest top-level directories ---'
+          sudo du -xhd1 / 2>/dev/null | sort -h | tail -n 15 || true
+
+          # GitHub-hosted Ubuntu images contain many preinstalled SDKs and
+          # toolchains that MotorSignal does not use. Remove only disposable
+          # software; keep Android SDK command-line tools, platform-tools,
+          # the active API/build-tools, CMake and NDK installations intact.
+          sudo rm -rf /usr/share/dotnet \
+            /usr/local/share/powershell \
+            /opt/ghc \
+            /usr/local/.ghcup \
+            /usr/local/lib/android/sdk/emulator \
+            /usr/local/lib/android/sdk/system-images
+
+          sudo apt-get clean || true
+          sudo rm -rf /var/lib/apt/lists/*
+          docker system prune -af --volumes 2>/dev/null || true
+
+          echo '--- Disk usage after cleanup ---'
+          df -h /
+          AVAILABLE_KB="$(df --output=avail / | tail -n 1 | tr -d ' ')"
+          MIN_AVAILABLE_KB=$((5 * 1024 * 1024))
+          if [ "$AVAILABLE_KB" -lt "$MIN_AVAILABLE_KB" ]; then
+            echo "ERROR: less than 5 GiB remains on the runner after cleanup."
+            exit 1
+          fi
+
       - name: Create Flutter local.properties
         shell: bash
         run: |
@@ -86,6 +118,7 @@ jobs:
           flutter doctor -v
           java -version
           sdkmanager --list_installed | grep -E 'platforms;android-37|build-tools;37|platform-tools' || true
+          df -h /
 
       - name: Get dependencies
         run: flutter pub get
@@ -97,7 +130,12 @@ jobs:
         run: flutter test
 
       - name: Build debug APK
-        run: flutter build apk --debug
+        shell: bash
+        run: |
+          set -euo pipefail
+          df -h /
+          flutter build apk --debug
+          df -h /
 
       - name: Verify debug APK
         shell: bash
@@ -135,7 +173,6 @@ jobs:
         with:
           distribution: temurin
           java-version: ${{ env.JAVA_VERSION }}
-          cache: gradle
 
       - name: Set up Flutter
         uses: subosito/flutter-action@v2
@@ -144,6 +181,37 @@ jobs:
           channel: stable
           cache: true
 
+      - name: Free runner disk space
+        shell: bash
+        run: |
+          set -euo pipefail
+          echo '--- Disk usage before cleanup ---'
+          df -h /
+          echo '--- Largest top-level directories ---'
+          sudo du -xhd1 / 2>/dev/null | sort -h | tail -n 15 || true
+
+          # Keep only software relevant to the Android build. Android SDK
+          # command-line tools, active SDK/build-tools, CMake and NDK are kept.
+          sudo rm -rf /usr/share/dotnet \
+            /usr/local/share/powershell \
+            /opt/ghc \
+            /usr/local/.ghcup \
+            /usr/local/lib/android/sdk/emulator \
+            /usr/local/lib/android/sdk/system-images
+
+          sudo apt-get clean || true
+          sudo rm -rf /var/lib/apt/lists/*
+          docker system prune -af --volumes 2>/dev/null || true
+
+          echo '--- Disk usage after cleanup ---'
+          df -h /
+          AVAILABLE_KB="$(df --output=avail / | tail -n 1 | tr -d ' ')"
+          MIN_AVAILABLE_KB=$((5 * 1024 * 1024))
+          if [ "$AVAILABLE_KB" -lt "$MIN_AVAILABLE_KB" ]; then
+            echo "ERROR: less than 5 GiB remains on the runner after cleanup."
+            exit 1
+          fi
+
       - name: Create Flutter local.properties
         shell: bash
         run: |
@@ -223,10 +291,20 @@ jobs:
             -alias "$KEY_ALIAS" >/dev/null
 
       - name: Build release APK
-        run: flutter build apk --release
+        shell: bash
+        run: |
+          set -euo pipefail
+          df -h /
+          flutter build apk --release
+          df -h /
 
       - name: Build release App Bundle
-        run: flutter build appbundle --release
+        shell: bash
+        run: |
+          set -euo pipefail
+          df -h /
+          flutter build appbundle --release
+          df -h /
 
       - name: Verify release artifacts and signatures
         shell: bash