fix: VST3 teardown under lock + re-attach hang + editor window on replace

- InstrumentEngineManager::assign: destroy replaced instrument OUTSIDE mu_
  (VST3 terminate/removed can block -> audio loop stall -> bridge Not
  Responding, transport stop hangs, notes never off)
- main.cpp LOAD job: DestroyWindow any open editor window of the channel
  before assign (replace VSTi -> SF2 with editor alive hung in removed())
- Vst3Instrument: reload() fresh plugin instance on second openGUI after
  close (Nexus etc. hang at view->attached() twice on same component)

native_bridge/src/Vst3Instrument.cpp

@@ -169,7 +169,8 @@ Vst3Instrument::Vst3Instrument()
       sampleRate_(44100.0),
       maxBlockSize_(256),
       loaded_(false),
-      guiAttached_(false) {}
+      guiAttached_(false),
+      hasAttachedOnce_(false) {}
 
 Vst3Instrument::~Vst3Instrument() {
 #ifdef HAVE_VST3SDK
@@ -489,6 +490,15 @@ bool Vst3Instrument::openGUI(void* parentWindowHandle) {
               << " controller=" << (s ? (s->controller ? 1 : 0) : -1) << std::endl;
     if (!s || !s->controller || !parentWindowHandle) return false;
     if (s->view && guiAttached_) return true;
+    if (hasAttachedOnce_ && !guiAttached_) {
+        // Reopen GUI sau khi dong: mot so plugin (Nexus...) hang o
+        // view->attached() LAN 2 tren cung component instance. Tao lai inst
+        // moi tren CUNG worker thread (COM STA con song) roi attach lai.
+        std::cerr << "[dbg] openGUI: re-attach - reloading fresh plugin instance" << std::endl;
+        if (!reload()) return false;
+        s = static_cast<Vst3HostState*>(state_);
+        if (!s || !s->controller) return false;
+    }
     IPlugView* rawView = nullptr;
     tresult qi = s->controller->queryInterface(IPlugView::iid, (void**)&rawView);
     {
@@ -539,6 +549,7 @@ bool Vst3Instrument::openGUI(void* parentWindowHandle) {
 #endif
     s->view = view;
     guiAttached_ = true;
+    hasAttachedOnce_ = true;
     // ponytail: the bridge loop is a worker thread without a Windows message
     // pump — some editors may not repaint until the first native event; a
     // future version can spin a dedicated UI thread + pump.
@@ -546,6 +557,31 @@ bool Vst3Instrument::openGUI(void* parentWindowHandle) {
 #endif
 }
 
+bool Vst3Instrument::reload() {
+#ifndef HAVE_VST3SDK
+    return false;
+#else
+    if (!state_) return false;
+    closeGUI();
+    auto* s = static_cast<Vst3HostState*>(state_);
+    if (s->component) {
+        FUnknownPtr<IAudioProcessor> processor(s->component);
+        if (processor) processor->setProcessing(false);
+        s->component->setActive(false);
+        s->component->terminate();
+    }
+    // Single-component plugins: controller == component, already terminated.
+    if (s->controller && !s->controllerIsComponent) s->controller->terminate();
+    s->processData.unprepare();
+    delete s;
+    state_ = nullptr;
+    loaded_ = false;
+    guiAttached_ = false;
+    hasAttachedOnce_ = false;
+    return loadPlugin(path_, sampleRate_);
+#endif
+}
+
 void Vst3Instrument::closeGUI() {
 #ifndef HAVE_VST3SDK
     return;