filter build targets to require a dockerfile

.github/workflows/build.yml

@@ -33,6 +33,18 @@ jobs:
 
           # Discover lanes: immediate subdirs under docker/
           mapfile -t ALL_LANES < <(find docker -mindepth 1 -maxdepth 1 -type d | sort)
+          # Filter to only directories that contain a Dockerfile (real lanes)
+          FILTERED_LANES=()
+          SKIPPED_LANES=()
+          for _d in "${ALL_LANES[@]}"; do
+            if [[ -f "${_d}/Dockerfile" ]]; then
+              FILTERED_LANES+=("${_d}")
+            else
+              SKIPPED_LANES+=("${_d}")
+            fi
+          done
+          ALL_LANES=("${FILTERED_LANES[@]}")
+
           # Also capture lane basenames (e.g. '7.4', 'nginx') for stable naming
           ALL_NAMES=()
           for _d in "${ALL_LANES[@]}"; do