fix: add max_items limit to fetch_all_edges to prevent unbounded memory growth

The fetch_all_nodes function has a max_items parameter (default 2000) to
prevent fetching too many items, but fetch_all_edges was missing this
safeguard. This could cause memory issues with graphs that have a large
number of edges.

Added _MAX_EDGES = 5000 as the default limit for edges, matching the
pattern already established for nodes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/utils/zep_paging.py

@@ -19,6 +19,7 @@ logger = get_logger('mirofish.zep_paging')
 
 _DEFAULT_PAGE_SIZE = 100
 _MAX_NODES = 2000
+_MAX_EDGES = 5000
 _DEFAULT_MAX_RETRIES = 3
 _DEFAULT_RETRY_DELAY = 2.0  # seconds, doubles each retry
 
@@ -106,6 +107,7 @@ def fetch_all_edges(
     client: Zep,
     graph_id: str,
     page_size: int = _DEFAULT_PAGE_SIZE,
+    max_items: int = _MAX_EDGES,
     max_retries: int = _DEFAULT_MAX_RETRIES,
     retry_delay: float = _DEFAULT_RETRY_DELAY,
 ) -> list[Any]:
@@ -132,6 +134,10 @@ def fetch_all_edges(
             break
 
         all_edges.extend(batch)
+        if len(all_edges) >= max_items:
+            all_edges = all_edges[:max_items]
+            logger.warning(f"Edge count reached limit ({max_items}), stopping pagination for graph {graph_id}")
+            break
         if len(batch) < page_size:
             break