More annotation added to the program

backend/routed_layout_preview.py

@@ -24,12 +24,16 @@ def create_routed_layout_svg(
 
     layout = yaml.safe_load(yaml_content) or {}
     cell_name = str(layout.get("name") or "layout")
+    # mxpic_router is kept as a sibling repository, so the backend adds it to
+    # sys.path only when the local checkout is available.
     router_root = os.path.abspath(os.path.join(os.path.dirname(__file__), "..", "..", "mxpic_router"))
     if os.path.isdir(router_root) and router_root not in sys.path:
         sys.path.insert(0, router_root)
     from mxpic_router import build_project_gds
 
     os.makedirs(os.path.dirname(output_path), exist_ok=True)
+    # Build into a temporary GDS first, then convert the generated top cell into
+    # the SVG preview consumed by the canvas.
     with tempfile.TemporaryDirectory(prefix="mxpic_routed_preview_") as temp_dir:
         temp_gds = os.path.join(temp_dir, f"{cell_name}.gds")
         build_project_gds(
@@ -49,7 +53,10 @@ def create_routed_layout_svg(
 
 
 def layout_has_links(yaml_content: str) -> bool:
+    """Detect whether a layout YAML document contains routed bundle links."""
     layout = yaml.safe_load(yaml_content) or {}
+    # Any bundle link means preview generation must use the routed builder
+    # instead of simple component placement.
     for bundle in (layout.get("bundles") or {}).values():
         links = bundle.get("links") or []
         if links: