fix(bridge): 3 bug âm thanh Qin/Nexus standalone

1) wavesynth tự phát khi mở app: probe calibrate() render vào live mix
   (renderAll process cùng instance) -> thêm calibratingCh_[16], renderAll
   bỏ qua channel đang calibrate; plugin_host panic (sustain off + all
   notes off + 128 noteOff) ngay sau preset apply để startup im lặng.
2) bấm GUI mở 2 cửa sổ Qin: sandbox VST2 child tự sở hữu top-level window
   -> ownsGuiWindow() + main.cpp forward OPEN_GUI control, không tạo native
   parent / không registry double-open.
3) play phát nhạc cụ sai: restore clobber — seed preset đè patch thật trong
   state file (ch3 63ba3667 -> 7f07473c) do saveStateJob chạy lúc child còn
   seed. Fix: queuePreset(waitApply=true) chờ child apply xong (presetOut
   memcmp), consume-before-apply (zero presetInLen trước khi apply), deferred
   double-load re-check trong main.cpp skip assign trùng path, watchdog
   respawn re-queue lastPreset_.

native_bridge/src/main.cpp

@@ -1129,6 +1129,24 @@ int main(int argc, char* argv[]) {
                     return;
                 }
             }
+            // G4.6: child-own GUI (sandbox VST2 like Qin). The child process
+            // opens its OWN top-level window on control 4 — no native parent
+            // window to create, no g_guiWindows registry, no same-path
+            // silencing, no closing of other editors (separate process;
+            // nothing to serialize). Just forward the OPEN_GUI control.
+            if (auto* inst0 = instruments.get(guiCh)) {
+                if (inst0->ownsGuiWindow()) {
+                    std::cerr << "[NativeBridge] GUI via child-own ch=" << guiCh
+                              << " plugin=" << arg2 << std::endl;
+                    try {
+                        inst0->attachView(nullptr);
+                    } catch (...) {
+                        std::cerr << "[NativeBridge] GUI child-own attach EXCEPTION ch=" << guiCh
+                                  << std::endl;
+                    }
+                    return;
+                }
+            }
             void* hwnd = (void*)arg1;
 #ifdef _WIN32
             HWND nativeHwnd = nullptr;
@@ -1577,6 +1595,23 @@ int main(int argc, char* argv[]) {
                     auto doAssign = std::function<void()>(
                         [&instruments, t, ch, path, sampleRate, block, spOld, spNew]() {
                         std::lock_guard<std::mutex> lg(g_loadMutex);
+                        // G4.6: deferred double-load re-check. Restore's
+                        // doRestore (also deferred via runOnMain) can assign
+                        // the SAME path FIRST — a second assign here replaces
+                        // the restored instance with a seed-only one (doAssign
+                        // applies NO preset) and clobbers the real patch in
+                        // the state file (ch3 63ba3667 -> 7f07473c observed).
+                        // Skip like the job-level guard; undo the silence.
+                        if (!path.empty() && !lower_plugin_path(ch).empty() &&
+                            lower_plugin_path(ch) == lower_path_str(path)) {
+                            std::cout << "[NativeBridge] LOAD skip (deferred re-check) ch=" << ch
+                                      << " path=" << path << std::endl;
+                            g_engine->setReloading(ch, false);
+                            for (uint32_t y : spOld) unmute_if_not_closing(y, "load-skip");
+                            for (uint32_t y : spNew) unmute_if_not_closing(y, "load-skip");
+                            g_stateDirty = true;
+                            return;
+                        }
                         bool ok = false;
                         try {
                             ok = instruments.assign(ch, t, path, sampleRate, block);