fix 5.2 audit findings on Windows: F-PROC-1 injection, F-MEM-5 UAF, F-PROC-2 restart race, F-PROC-3, F5, F6

native_bridge/include/NativeInstrumentEngine.h

@@ -79,6 +79,18 @@ public:
 
     INativeInstrument* get(uint32_t channel);
 
+    // F-MEM-5 (audit 5.2): get() releases mu_ before the caller derefs, so a
+    // worker thread's assign()/unload() can destroy the instance mid-use.
+    // has() is a safe existence check; withInstrument() runs code against the
+    // instance while mu_ is still held. Use these from non-Ui threads.
+    bool has(uint32_t channel);
+    template <typename F>
+    auto withInstrument(uint32_t channel, F&& fn) -> decltype(fn((INativeInstrument*)nullptr)) {
+        std::lock_guard<std::mutex> lock(mu_);
+        auto it = channels_.find(channel);
+        return fn(it == channels_.end() ? nullptr : it->second.get());
+    }
+
     // Real-time MIDI dispatch (audio loop thread). Each call holds mu_ for the
     // WHOLE call — lookup + reloading check + instrument call under one lock —
     // so a worker thread's assign()/unload() can never swap the map and destroy