fix: tail toggle/scroll now commits to ext-state immediately

markTailDirty() called MarkProjectDirty() but never called
saveToActiveProject(), so the new tail value was never written
to SetProjExtState. On unsaved projects saveToActiveProject()
no-ops cleanly, resolving the companion Major at the same time.

src/bank_panel.cpp

@@ -534,11 +534,15 @@ bool pointInFooter(int x, int y) {
     return f.top < f.bottom && x >= f.left && x < f.right && y >= f.top && y < f.bottom;
 }
 
-// Marks the active project dirty so a tail-setting change saves with the project.
-// A bare tail toggle dirtying the project is intended (it IS project state now).
-// persist writes the setting into ext state on the next save; this only flags that a
-// save is owed. NON-DESTRUCTIVE: touches nothing in the bank/arrange.
+// Commits the current tail setting to ext state and marks the active project dirty
+// so the change travels inside the .rpp on Ctrl+S. saveToActiveProject() is the only
+// path that calls SetProjExtState for the tail key — calling it here closes the gap
+// where toggle/scroll would dirty the project but the new value was never written.
+// On an unsaved project saveToActiveProject() no-ops cleanly (documented in persist.h).
+// MarkProjectDirty runs unconditionally so REAPER knows a save is owed either way.
+// NON-DESTRUCTIVE: touches nothing in the bank/arrange.
 void markTailDirty() {
+    if (g_panel.session) g_panel.session->saveToActiveProject();
     ReaProject* proj = EnumProjects(-1, nullptr, 0);
     if (proj) MarkProjectDirty(proj);
 }