diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index affa8b6..5a9f669 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -108,10 +108,18 @@ jobs:
       - uses: docker/setup-qemu-action@v3
       - uses: docker/setup-buildx-action@v3
 
+      - name: DEBUG registry username source
+        run: |
+          echo "Selected registry username source: $SOURCE"
+        # Do NOT echo the username or any secret values — only indicate which source will be used
+        env:
+          SOURCE: ${{ inputs.REGISTRY_USER != '' && 'inputs' || secrets.REGISTRY_USER != '' && 'secrets' || vars.REGISTRY_USER != '' && 'vars' || 'actor' }}
+
       - uses: docker/login-action@v3
         with:
           registry: gitea.auvem.com
-          username: ${{ inputs.REGISTRY_USER }}
+          # Resolve username in this order: workflow input -> repo/secret -> repo var -> actor
+          username: ${{ inputs.REGISTRY_USER != '' && inputs.REGISTRY_USER || secrets.REGISTRY_USER != '' && secrets.REGISTRY_USER || vars.REGISTRY_USER != '' && vars.REGISTRY_USER || github.actor }}
           password: ${{ secrets.REGISTRY_TOKEN }}
 
       - name: Derive image name and tags