Ψ-W1-T2: disjoint per-mode solo surfaces and a playback-gated mode switch

Solo is cached, cleared and replayed per mode on a real switch only; the switch is refused visibly while the transport runs. The footer segment now routes through the activate actions, so a panel switch finally persists.

src/shell/actions/design_view_actions.cpp

@@ -36,6 +36,7 @@
 #define REAPERAPI_WANT_GetMediaTrackInfo_Value
 #define REAPERAPI_WANT_EnumProjects
 #define REAPERAPI_WANT_Main_SaveProject
+#define REAPERAPI_WANT_Help_Set
 #define REAPERAPI_WANT_ShowConsoleMsg
 #define REAPERAPI_WANT_Undo_BeginBlock2
 #define REAPERAPI_WANT_Undo_EndBlock2
@@ -160,21 +161,29 @@ void persistViewState() {
     g_session->saveToActiveProject();
 }
 
+// The footer segment already reads disabled while the transport runs, but an action can
+// be fired with the panel closed — so the refusal also lands as a status line. Guarded on
+// the transport because applyMode's other refusal is an unregistered mode id.
+void reportModeSwitchRefused() {
+    if (transportBlocksModeSwitch(nullptr) && Help_Set)
+        Help_Set("ReaSampler: stop the transport to switch view mode", true);
+}
+
 // Cycle to the next mode in ordinal order. applyMode itself sets the model's active
 // mode, so we only compute the target and apply.
 void doToggleMode() {
     const std::string target =
         nextModeId(g_session->view().modes(), g_session->view().activeModeId());
     if (target.empty()) return;  // no modes to cycle to (degenerate)
-    applyMode(g_session->view(), target, nullptr);
+    if (!applyMode(g_session->view(), target, nullptr)) { reportModeSwitchRefused(); return; }
     persistViewState();
     bankPanelInvalidate();  // repaint the footer [Arrange|Design] toggle immediately
 }
 
 // Direct jump to a named mode. applyMode is a no-op (returns false, no mutation) if
-// the id is unregistered, so an absent mode fails safe.
+// the id is unregistered or the transport is running, so both fail safe.
 void doActivateMode(const std::string& modeId) {
-    applyMode(g_session->view(), modeId, nullptr);
+    if (!applyMode(g_session->view(), modeId, nullptr)) { reportModeSwitchRefused(); return; }
     persistViewState();
     bankPanelInvalidate();  // repaint the footer [Arrange|Design] toggle immediately
 }