native_bridge: recalibrate after preset restore, reject 3rd live VST2 instance

native_bridge/include/NativeInstrumentEngine.h

@@ -158,6 +158,11 @@ public:
     void setBypassed(bool on) { isBypassed_.store(on); }
     bool isBypassed() const { return isBypassed_.load(); }
 
+    // Re-run output calibration after a preset/chunk restore (calibrate() in
+    // assign() runs BEFORE the preset exists - VST2 like Qin probes silent and
+    // stays at makeup=1.0, quieter than VSTi calibrated after restore).
+    float recalibrate(uint32_t channel, double sampleRate, uint32_t blockSize);
+
 private:
     static std::unique_ptr<INativeInstrument> create_instrument(InstrumentType type);
     // Probe-render 3 notes sau khi load, do peak, tinh makeup de note don ra

native_bridge/src/NativeInstrumentEngine.cpp

@@ -276,6 +276,23 @@ bool InstrumentEngineManager::assign(uint32_t channel, InstrumentType type,
     return true;
 }
 
+float InstrumentEngineManager::recalibrate(uint32_t channel, double sampleRate, uint32_t blockSize) {
+    INativeInstrument* inst = nullptr;
+    {
+        std::lock_guard<std::mutex> lock(mu_);
+        auto it = channels_.find(channel);
+        if (it != channels_.end()) inst = it->second.get();
+    }
+    if (!inst) return 1.0f;
+    // calibrate() probe-renders (up to ~0.9s) - never hold mu_ (audio stall).
+    const float mk = calibrate(inst, sampleRate, blockSize);
+    {
+        std::lock_guard<std::mutex> lock(mu_);
+        makeup_[channel] = mk;
+    }
+    return mk;
+}
+
 void InstrumentEngineManager::unload(uint32_t channel) {
     if (channel >= 16) return;
     // Destructor runs on the CALLER thread (VST3 terminate must run on the

native_bridge/src/main.cpp

@@ -1355,10 +1355,44 @@ int main(int argc, char* argv[]) {
                         }
                         if (ok) {
                             if (auto* inst = instruments.get(ch)) {
-                                if ((t == InstrumentType::VST3 || t == InstrumentType::VST2) && !preset.empty())
-                                    inst->loadSerializedState(preset);
-                                else
-                                    inst->selectProgram(ch, bank, program);
+                                // QIN LIMIT: same-path VST2 instance #3 would
+                                // flood auxhost with ML_RELEASE_ERROR (engine
+                                // supports 2 live instances max). Restore skips
+                                // it; frontend keeps the track but muted/empty.
+                                if (t == InstrumentType::VST2 && !path.empty()) {
+                                    uint32_t samePath = 0;
+                                    for (uint32_t y = 0; y < 16; ++y) {
+                                        if (y == ch) continue;
+                                        if (!instruments.get(y)) continue;
+                                        if (lower_plugin_path(y) == lower_path_str(path)) ++samePath;
+                                    }
+                                    if (samePath >= 2) {
+                                        std::cerr << "[NativeBridge] restore SKIP ch=" << ch
+                                                  << " VST2 path already has " << samePath
+                                                  << " live instances (" << path
+                                                  << ") - plugin engine supports 2 max" << std::endl;
+                                        instruments.unload(ch);
+                                        ok = false;
+                                    }
+                                }
+                            }
+                            if (ok) {
+                                auto* inst2 = instruments.get(ch);
+                                if (!inst2) {
+                                    std::cerr << "[NativeBridge] restore lost inst ch=" << ch << std::endl;
+                                } else {
+                                    if ((t == InstrumentType::VST3 || t == InstrumentType::VST2) && !preset.empty())
+                                        inst2->loadSerializedState(preset);
+                                    else
+                                        inst2->selectProgram(ch, bank, program);
+                                // Re-calibrate AFTER the preset exists: assign()
+                                // calibrated the empty instance (VST2 like Qin
+                                // probes silent -> makeup=1.0, quieter than the
+                                // other VSTi). Probe-render runs off mu_ so the
+                                // audio loop never stalls.
+                                    if (t == InstrumentType::VST3 || t == InstrumentType::VST2)
+                                        instruments.recalibrate(ch, sampleRate, block);
+                                }
                             }
                             std::cout << "[NativeBridge] restored ch=" << ch
                                       << " type=" << (int)t << " " << path << std::endl;
@@ -1421,6 +1455,27 @@ int main(int argc, char* argv[]) {
                                   << " (already loaded: " << path << ")" << std::endl;
                         return;
                     }
+                    // QIN LIMIT: Kong Audio Qin bridges all instances through
+                    // ONE auxhost.exe (32-bit engine host); a 3rd live Qin
+                    // instance makes the engine spam ML_RELEASE_ERROR forever
+                    // (observed: ch0+ch3 fine, +ch2 -> bridge log flooded,
+                    // engine unusable). Reject VST2 instance #3 of the same
+                    // path so the session stays playable.
+                    if (t == InstrumentType::VST2 && !path.empty()) {
+                        uint32_t samePath = 0;
+                        for (uint32_t y = 0; y < 16; ++y) {
+                            if (y == ch) continue;
+                            if (!instruments.get(y)) continue;
+                            if (lower_plugin_path(y) == lower_path_str(path)) ++samePath;
+                        }
+                        if (samePath >= 2) {
+                            std::cerr << "[NativeBridge] LOAD REJECT ch=" << ch
+                                      << " VST2 path already has " << samePath
+                                      << " live instances (" << path
+                                      << ") - plugin engine supports 2 max" << std::endl;
+                            return;
+                        }
+                    }
                     // CRASH FIX: this job enters the plugin DLL (createInstance
                     // in loadPlugin, old-instance terminate on replace) while
                     // the audio loop may process() another instance of the SAME