diff --git a/ai/shared.md b/ai/shared.md
index eb2bd6b..d2872ea 100644
--- a/ai/shared.md
+++ b/ai/shared.md
@@ -20,8 +20,9 @@ these rules.
 - Persisted schedules must not reference their source set or selected level.
   Persisted assignments must not reference their source elements. Later
   source edits or deletions must not change an existing schedule.
-- Schedule recalculation must preserve completed work while redistributing
-  unfinished assignments across the remaining dates.
+- Schedule recalculation must preserve completed work and the schedule's
+  original start date. Treat the requested start as the boundary for
+  redistributing unfinished assignments, and update the target date.
 - Planned features in `README.md` are future ideas, not authorized scope.
 - The Laravel backend exists under `backend/`.
 - The standalone Vue frontend exists under `frontend/website/`.