diff --git a/core/models.py b/core/models.py
index b21b1af..48077d2 100644
--- a/core/models.py
+++ b/core/models.py
@@ -274,19 +274,29 @@ def get_children(conn: sqlite3.Connection, task_id: str) -> list[dict]:
     return _rows_to_list(rows)
 
 
-def has_open_children(conn: sqlite3.Connection, task_id: str) -> bool:
+def has_open_children(conn: sqlite3.Connection, task_id: str, visited: set[str] | None = None) -> bool:
     """Recursively check if task has any open (not done/cancelled) descendants."""
+    if visited is None:
+        visited = set()
+    if task_id in visited:
+        return False
+    visited = visited | {task_id}
     children = get_children(conn, task_id)
     for child in children:
         if child["status"] not in ("done", "cancelled"):
             return True
-        if has_open_children(conn, child["id"]):
+        if has_open_children(conn, child["id"], visited):
             return True
     return False
 
 
-def _check_parent_completion(conn: sqlite3.Connection, task_id: str) -> None:
+def _check_parent_completion(conn: sqlite3.Connection, task_id: str, visited: set[str] | None = None) -> None:
     """Cascade-check upward: if parent is 'revising' and all children closed → promote to 'done'."""
+    if visited is None:
+        visited = set()
+    if task_id in visited:
+        return
+    visited = visited | {task_id}
     task = get_task(conn, task_id)
     if not task:
         return
@@ -305,7 +315,7 @@ def _check_parent_completion(conn: sqlite3.Connection, task_id: str) -> None:
             (now, now, parent_id),
         )
         conn.commit()
-        _check_parent_completion(conn, parent_id)
+        _check_parent_completion(conn, parent_id, visited)
 
 
 VALID_TASK_SORT_FIELDS = frozenset({