refactor

backend/rules.py

@@ -50,14 +50,26 @@ async def load_learnstate() -> tuple[list[dict], dict[str, dict[str, set[str]]]]
     return await list_guides(), levels
 
 
+_content_cache: dict[str, tuple[float, dict | None]] = {}
+
+
 def _content_json(topic: str, fmt: str) -> dict | None:
+    """Guide-Content-JSON (kann MB groß sein), mtime-gecacht — /stats und /topics/progress
+    lasen die Datei bei JEDEM Frontend-Poll neu und synchron im Event-Loop."""
     path = guide_content_path(topic, fmt)
-    if not path.exists():
-        return None
     try:
-        return json.loads(path.read_text(encoding="utf-8"))
-    except ValueError:
+        mtime = path.stat().st_mtime
+    except OSError:
+        _content_cache.pop(str(path), None)
         return None
+    cached = _content_cache.get(str(path))
+    if cached is None or cached[0] != mtime:
+        try:
+            data = json.loads(path.read_text(encoding="utf-8"))
+        except ValueError:
+            data = None
+        _content_cache[str(path)] = (mtime, data)
+    return _content_cache[str(path)][1]