diff --git a/core/models.py b/core/models.py
index fe85d36..ba13f18 100644
--- a/core/models.py
+++ b/core/models.py
@@ -290,13 +290,11 @@ def has_open_children(conn: sqlite3.Connection, task_id: str, visited: set[str]
     return False
 
 
-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()
+def _do_cascade(conn: sqlite3.Connection, task_id: str, visited: set[str]) -> None:
+    """Recursive upward cascade without transaction management — no commits."""
     if task_id in visited:
         return
-    visited = visited | {task_id}
+    visited.add(task_id)
     task = get_task(conn, task_id)
     if not task:
         return
@@ -314,8 +312,19 @@ def _check_parent_completion(conn: sqlite3.Connection, task_id: str, visited: se
             "UPDATE tasks SET status = 'done', completed_at = ?, updated_at = ? WHERE id = ?",
             (now, now, parent_id),
         )
+        _do_cascade(conn, parent_id, visited)
+
+
+def _check_parent_completion(conn: sqlite3.Connection, task_id: str, visited: set[str] | None = None) -> None:
+    """Cascade-check upward: promote all ready parents to 'done' in one atomic transaction."""
+    if visited is None:
+        visited = set()
+    try:
+        _do_cascade(conn, task_id, visited)
         conn.commit()
-        _check_parent_completion(conn, parent_id, visited)
+    except Exception:
+        conn.rollback()
+        raise
 
 
 VALID_TASK_SORT_FIELDS = frozenset({