fix: robust mermaid injection with utf-8 encoding and error check

build-slides.sh

@@ -33,4 +33,49 @@ else
     marpteam/marp-cli --html --output /home/marp/output "${REL_SLIDES[@]}"
 fi
 
+# Inject mermaid.js into any HTML that contains mermaid code blocks.
+# Marp emits fenced mermaid blocks as <pre><code class="language-mermaid">.
+# The script finds those elements, replaces them with <div class="mermaid">,
+# then loads and runs mermaid.js from CDN.
+inject_mermaid() {
+  local html_file="$1"
+  python3 - "$html_file" << 'PYEOF'
+import sys
+
+path = sys.argv[1]
+snippet = """\
+<script type="module">
+import mermaid from 'https://cdn.jsdelivr.net/npm/mermaid@11/dist/mermaid.esm.min.mjs';
+document.querySelectorAll('code.language-mermaid').forEach(el => {
+  const div = document.createElement('div');
+  div.className = 'mermaid';
+  div.textContent = el.textContent;
+  el.closest('pre').replaceWith(div);
+});
+mermaid.initialize({ startOnLoad: true, theme: 'dark' });
+</script>"""
+
+with open(path, encoding='utf-8') as f:
+    content = f.read()
+new_content = content.replace('</body>', snippet + '\n</body>', 1)
+if new_content == content:
+    print(f"Warning: </body> not found in {path}", file=sys.stderr)
+    sys.exit(1)
+with open(path, 'w', encoding='utf-8') as f:
+    f.write(new_content)
+PYEOF
+}
+
+if command -v python3 &>/dev/null; then
+  for html_file in "$OUTPUT_DIR"/*.html; do
+    [ -f "$html_file" ] || continue
+    if grep -q 'class="language-mermaid"' "$html_file"; then
+      inject_mermaid "$html_file"
+      echo "  Injected mermaid.js into $(basename "$html_file")"
+    fi
+  done
+else
+  echo "Warning: python3 not found — skipping mermaid injection"
+fi
+
 echo "Done — slides in $OUTPUT_DIR/"