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

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