fix: plan mode flexibility (#517)

Co-authored-by: Letta <noreply@letta.com>

src/tools/impl/ExitPlanMode.ts

@@ -9,6 +9,10 @@ export async function exit_plan_mode(): Promise<{ message: string }> {
   // The UI layer checks if the plan file exists and auto-rejects if not
   return {
     message:
-      "User has approved your plan. You can now start coding.\nStart with updating your todo list if applicable",
+      "User has approved your plan. You can now start coding.\n" +
+      "Start with updating your todo list if applicable.\n\n" +
+      "Tip: If this plan will be referenced in the future by your future-self, " +
+      "other agents, or humans, consider renaming the plan file to something easily " +
+      "identifiable with a timestamp (e.g., `2026-01-auth-refactor.md`) rather than the random name.",
   };
 }