Narrow the mode switch's persist to the one key it changes

A switch wrote all seven ext-state keys to record that view_state moved,
re-serializing the bank book and the tracking ledger for nothing. Both entry
surfaces now take saveViewStateOnly; every other caller keeps the full save.

src/shell/actions/design_view_actions.cpp

@@ -133,11 +133,17 @@ std::vector<RetagItem> selectedRetagItems() {
     return items;
 }
 
+// Which keys the following persist has to write. A mode switch changes `view_state`
+// and nothing else, and it is the one action here a user fires repeatedly — so it
+// alone narrows, and pays neither the bank-book nor the tracking-ledger
+// serialization. Every other action keeps the full save.
+enum class PersistScope { Full, ViewOnly };
+
 // Persists the bank + Design-View model after every state-changing action so the
 // view model is not lost across save/close/reopen. If membership is non-empty and
 // the project is unsaved, prompts Save-As first (mirrors the flow capture uses) —
 // DAW-ONLY: Main_SaveProject(proj, true) blocks until the dialog is dismissed.
-void persistViewState() {
+void persistViewState(PersistScope scope) {
     if (!g_session->view().membership().empty()) {
         ReaProject* proj = EnumProjects(-1, nullptr, 0);
         if (proj) {
@@ -158,7 +164,8 @@ void persistViewState() {
             }
         }
     }
-    g_session->saveToActiveProject();
+    if (scope == PersistScope::ViewOnly) g_session->saveViewStateOnly();
+    else                                 g_session->saveToActiveProject();
 }
 
 // The footer segment already reads disabled while the transport runs, but an action can
@@ -178,7 +185,7 @@ void doToggleMode() {
         nextModeId(g_session->view().modes(), g_session->view().activeModeId());
     if (target.empty()) return;  // no modes to cycle to (degenerate)
     if (!applyMode(g_session->view(), target, nullptr)) { reportModeSwitchRefused(); return; }
-    persistViewState();
+    persistViewState(PersistScope::ViewOnly);
     bankPanelInvalidate();  // repaint the footer [Arrange|Design] toggle immediately
 }
 
@@ -186,7 +193,7 @@ void doToggleMode() {
 // the id is unregistered or the transport is running, so both fail safe.
 void doActivateMode(const std::string& modeId) {
     if (!applyMode(g_session->view(), modeId, nullptr)) { reportModeSwitchRefused(); return; }
-    persistViewState();
+    persistViewState(PersistScope::ViewOnly);
     bankPanelInvalidate();  // repaint the footer [Arrange|Design] toggle immediately
 }
 
@@ -196,7 +203,7 @@ void doTag(const std::string& modeId) {
     for (const std::string& g : selectedTrackGuids())
         g_session->view().membership().tag(g, modeId);
     reapplyActiveMode();
-    persistViewState();
+    persistViewState(PersistScope::Full);
 }
 
 // Shared body behind "Untag selected" and "Tag -> Arrange" — Arrange is the absence
@@ -205,7 +212,7 @@ void doUntag() {
     for (const std::string& g : selectedTrackGuids())
         g_session->view().membership().untag(g);
     reapplyActiveMode();
-    persistViewState();
+    persistViewState(PersistScope::Full);
 }
 
 // Flips each track's pin independently — the honest semantics of a toggle on a
@@ -215,7 +222,7 @@ void doShowBoth() {
     for (const std::string& g : selectedTrackGuids())
         m.setShowBoth(g, !m.isShowBoth(g));
     reapplyActiveMode();
-    persistViewState();
+    persistViewState(PersistScope::Full);
 }
 
 // Retag the current ITEM selection to `targetMode` (empty => untag -> Arrange
@@ -247,7 +254,7 @@ void doMoveItems(const std::string& targetMode) {
             : std::string("ReaSampler: move selected items -> ") + targetMode;
     Undo_EndBlock2(nullptr, label.c_str(), -1);
 
-    persistViewState();
+    persistViewState(PersistScope::Full);
 }
 
 }  // namespace