diff --git a/.gitea/workflows/build.yml b/.gitea/workflows/build.yml
index d708e39..9fd121f 100644
--- a/.gitea/workflows/build.yml
+++ b/.gitea/workflows/build.yml
@@ -20,6 +20,46 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
+      - name: Preflight disk cleanup
+        shell: bash
+        run: |
+          set -euo pipefail
+
+          run_sudo() {
+            if command -v sudo >/dev/null 2>&1; then
+              sudo "$@"
+            else
+              "$@"
+            fi
+          }
+
+          free_mb() {
+            df -Pm "${1:-/}" | awk 'NR==2 {print $4}'
+          }
+
+          echo "Disk usage before cleanup:"
+          df -h
+
+          if command -v docker >/dev/null 2>&1; then
+            docker system prune -af --volumes || true
+            docker builder prune -af || true
+          fi
+
+          run_sudo rm -rf /tmp/* /var/tmp/* || true
+
+          if [ "$(free_mb /)" -lt 8192 ]; then
+            echo "Free disk space is below 8GB. Cleaning user build caches..."
+            rm -rf "$HOME/.gradle/caches" "$HOME/.gradle/wrapper/dists" "$HOME/.pub-cache/_temp" || true
+          fi
+
+          echo "Disk usage after cleanup:"
+          df -h
+
+          if [ "$(free_mb /)" -lt 4096 ]; then
+            echo "Free disk space is still below 4GB after cleanup. Runner disk is effectively full."
+            exit 1
+          fi
+
       - name: Checkout
         uses: actions/checkout@v4
         with:
@@ -68,6 +108,8 @@ jobs:
         run: |
           set -euo pipefail
 
+          rm -rf build dist .dart_tool android/.gradle
+
           pkg_dir="$PWD/dist/android"
           if [ -d "$pkg_dir" ]; then
             echo "Cleaning old Android build artifacts: $pkg_dir"
@@ -202,3 +244,15 @@ jobs:
             -H "Authorization: token $GITEA_TOKEN" \
             -F "attachment=@gongyun-app-release.apk" \
             "$assets_url?name=gongyun-app-release.apk"
+
+      - name: Post-build disk cleanup
+        if: always()
+        shell: bash
+        run: |
+          set -euo pipefail
+          rm -rf build dist .dart_tool android/.gradle android/app-release.jks android/key.properties || true
+          if command -v docker >/dev/null 2>&1; then
+            docker system prune -af --volumes || true
+            docker builder prune -af || true
+          fi
+          df -h