fix fallback to fresh retrieval on corrupted Redis cache

src/rag/router.py

@@ -116,9 +116,12 @@ class RetrievalRouter:
 
         cached = await redis.get(cache_key)
         if cached:
-            logger.info("returning cached retrieval results", source_hint=source_hint)
-            raw = json.loads(cached)
-            return [RetrievalResult(**r) for r in raw]
+            try:
+                raw = json.loads(cached)
+                logger.info("returning cached retrieval results", source_hint=source_hint)
+                return [RetrievalResult(**r) for r in raw]
+            except Exception:
+                logger.warning("corrupted retrieval cache, fetching fresh", cache_key=cache_key)
 
         results = await self._retrieve_uncached(query, user_id, source_hint, k)