Capture runner build failures

.gitea/workflows/build.yml

@@ -20,7 +20,10 @@ jobs:
           java-version: '21'
 
       - name: Build
-        run: ./gradlew build --stacktrace --no-configuration-cache
+        shell: bash
+        run: |
+          set -o pipefail
+          ./gradlew build --stacktrace --no-configuration-cache 2>&1 | tee build.log
 
       - name: Upload mod jar
         uses: actions/upload-artifact@v3
@@ -29,6 +32,22 @@ jobs:
           name: explosionoverhaul-neoforge-build
           path: |
             build/libs/**
+            build.log
+
+      - name: Publish failure log branch
+        if: failure()
+        shell: bash
+        run: |
+          set -euo pipefail
+          git config user.name "gitea-actions"
+          git config user.email "actions@git.wilkensxl.de"
+          git checkout --orphan build-failure
+          git rm -rf . || true
+          mkdir -p logs
+          cp build.log logs/build.log
+          git add logs/build.log
+          git commit -m "Update build failure log [skip ci]"
+          git push --force origin HEAD:build-failure
 
       - name: Publish private test jar branch
         if: success()