- name: Checkout repository
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
 
+      - name: Check for leading BOM (Byte Order Mark)
+        id: bom
+        run: |
+          # Separate leading-BOM check (issue `#70` requirement).
+          # U+FEFF BOM at file start is a distinct check from general invisible characters.
+          # BOM as UTF-8 bytes: ef bb bf
+          set +e
+          find "$GITHUB_WORKSPACE" \
+            -not -path '*/.git/*' -not -path '*/node_modules/*' \
+            -not -path '*/.deno/*' -not -path '*/target/*' \
+            -not -path '*/_build/*' -not -path '*/deps/*' \
+            -not -path '*/external_corpora/*' -not -path '*/.lake/*' \
+            -type f \( -name '*.rs' -o -name '*.ex' -o -name '*.exs' -o -name '*.res' \
+              -o -name '*.js' -o -name '*.ts' -o -name '*.json' -o -name '*.toml' \
+              -o -name '*.yml' -o -name '*.yaml' -o -name '*.md' -o -name '*.adoc' \
+              -o -name '*.idr' -o -name '*.zig' -o -name '*.v' -o -name '*.jl' \
+              -o -name '*.gleam' -o -name '*.hs' -o -name '*.ml' -o -name '*.sh' \) \
+            -exec grep -aPl '^\xef\xbb\xbf' {} \; > /tmp/bom-results.txt 2>/dev/null
+          BOM_EXIT=$?
+          set -e
+
+          BOM_COUNT=$(wc -l < /tmp/bom-results.txt 2>/dev/null || echo 0)
+          echo "bom_count=$BOM_COUNT" >> "$GITHUB_OUTPUT"
+
+          # Emit warnings for files with leading BOM
+          while IFS= read -r filepath; do
+            [ -z "$filepath" ] && continue
+            REL_PATH="${filepath#$GITHUB_WORKSPACE/}"
+            echo "::warning file=${REL_PATH}::File starts with UTF-8 BOM (U+FEFF) - consider removing for better compatibility"
+          done < /tmp/bom-results.txt
+
+          if [ "${BOM_COUNT:-0}" -gt 0 ]; then
+            echo "::notice::$BOM_COUNT file(s) have leading BOM - advisory only"
+          fi
+
       - name: Scan for invisible characters
         id: lint
         run: |

 
       - name: Write summary
         run: |
+          echo "## Empty-Linter Results" >> "$GITHUB_STEP_SUMMARY"
+          echo "" >> "$GITHUB_STEP_SUMMARY"
+
+          # BOM check results
+          BOM_COUNT="${{ steps.bom.outputs.bom_count }}"
+          if [ "${BOM_COUNT:-0}" -gt 0 ] 2>/dev/null; then
+            echo "- **Leading BOM**: Found **${BOM_COUNT}** file(s) with UTF-8 BOM at start (advisory)" >> "$GITHUB_STEP_SUMMARY"
+          else
+            echo "- **Leading BOM**: :white_check_mark: No leading BOM detected" >> "$GITHUB_STEP_SUMMARY"
+          fi
+
+          # General invisible character results
           if [ "${{ steps.lint.outputs.ready }}" = "true" ]; then
             FINDINGS="${{ steps.lint.outputs.findings }}"
-            if [ "$FINDINGS" -gt 0 ] 2>/dev/null; then
-              echo "## Empty-Linter Results" >> "$GITHUB_STEP_SUMMARY"
-              echo "" >> "$GITHUB_STEP_SUMMARY"
-              echo "Found **${FINDINGS}** invisible character issue(s). See annotations above." >> "$GITHUB_STEP_SUMMARY"
+            BLOCKING="${{ steps.lint.outputs.blocking }}"
+            if [ "${BLOCKING:-0}" -gt 0 ] 2>/dev/null; then
+              echo "- **C0/NUL corruption**: :x: **${BLOCKING}** file(s) with blocking corruption" >> "$GITHUB_STEP_SUMMARY"
+            elif [ "$FINDINGS" -gt 0 ] 2>/dev/null; then
+              echo "- **Invisible Unicode**: Found **${FINDINGS}** file(s) (advisory)" >> "$GITHUB_STEP_SUMMARY"
             else
-              echo "## Empty-Linter Results" >> "$GITHUB_STEP_SUMMARY"
-              echo "" >> "$GITHUB_STEP_SUMMARY"
-              echo ":white_check_mark: No invisible character issues found." >> "$GITHUB_STEP_SUMMARY"
+              echo "- **Invisible characters**: :white_check_mark: No issues found" >> "$GITHUB_STEP_SUMMARY"
             fi
           else
-            echo "## Empty-Linter" >> "$GITHUB_STEP_SUMMARY"
-            echo "" >> "$GITHUB_STEP_SUMMARY"
-            echo "Skipped: empty-linter not available." >> "$GITHUB_STEP_SUMMARY"
+            echo "- **Invisible characters**: Skipped (empty-linter not available)" >> "$GITHUB_STEP_SUMMARY"
           fi
 
   # ---------------------------------------------------------------------------