ci: add concurrency group to prevent duplicate runner builds

.gitea/workflows/android-build.yml

@@ -4,6 +4,12 @@ on:
   push:
   workflow_dispatch:
 
+# Only one run per branch at a time. A new push cancels any in-progress run,
+# preventing duplicate builds when the runner picks up the same event twice.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 permissions:
   contents: write   # required for creating releases
   packages: write
@@ -94,11 +100,21 @@ jobs:
 
       - name: Build Debug APK
         working-directory: android
-        run: ./gradlew assembleDebug --no-daemon
+        run: |
+          # Retry up to 3 times to survive transient network errors when the
+          # Gradle wrapper downloads its distribution from GitHub CDN.
+          for attempt in 1 2 3; do
+            ./gradlew assembleDebug --no-daemon && break
+            [ "$attempt" -lt 3 ] && echo "Attempt $attempt failed — retrying in 30s..." && sleep 30 || exit 1
+          done
 
       - name: Build Release APK (unsigned — no signing key required)
         working-directory: android
-        run: ./gradlew assembleRelease --no-daemon
+        run: |
+          for attempt in 1 2 3; do
+            ./gradlew assembleRelease --no-daemon && break
+            [ "$attempt" -lt 3 ] && echo "Attempt $attempt failed — retrying in 30s..." && sleep 30 || exit 1
+          done
 
       # ── 9. Upload APKs as workflow artifacts ─────────────────────────────────
       - name: Upload APKs as artifacts