Out-of-process rebuild: Add Plugin/HelperConnection.h/.cpp — spawns helper, IPC, crash detection

Source/Plugin/HelperConnection.h

@@ -0,0 +1,68 @@
+#pragma once
+
+#include <juce_core/juce_core.h>
+#include <string>
+#include <thread>
+#include <atomic>
+#include <functional>
+#include <mutex>
+
+#include "../Shared/SharedAudioBuffer.h"
+#include "../Shared/IPCProtocol.h"
+
+class HelperConnection : private juce::Timer
+{
+public:
+    HelperConnection();
+    ~HelperConnection();
+
+    // Lifecycle
+    bool spawnHelper();
+    void killHelper();
+    bool isHelperRunning() const { return helperRunning.load(); }
+
+    // Audio bridge
+    SharedAudioBuffer& getSharedAudio() { return sharedAudio; }
+    SharedSemaphore& getInputSem() { return inputSem; }
+    SharedSemaphore& getOutputSem() { return outputSem; }
+
+    // Send commands (blocking — waits for response)
+    std::string sendCommand(const std::string& json);
+
+    // State
+    enum class State { Disconnected, Starting, Connected, Crashed };
+    State getState() const { return state.load(); }
+
+    // Callbacks
+    std::function<void()> onHelperReady;
+    std::function<void()> onHelperCrashed;
+    std::function<void(int, float)> onParamChanged;
+
+private:
+    void timerCallback() override;
+    void ipcListenLoop();
+    void handleNotification(const std::string& json);
+
+    // Helper process
+    pid_t helperPid = 0;
+    std::atomic<bool> helperRunning{false};
+    std::atomic<State> state{State::Disconnected};
+
+    // Shared memory
+    SharedAudioBuffer sharedAudio;
+    SharedSemaphore inputSem;
+    SharedSemaphore outputSem;
+
+    // IPC socket (parent is server)
+    int serverSocketFd = -1;
+    int clientSocketFd = -1;  // connection from helper
+    std::thread ipcThread;
+    std::atomic<bool> ipcRunning{false};
+
+    // Command/response synchronization
+    std::mutex commandMutex;
+    std::string lastResponse;
+    std::atomic<bool> responseReady{false};
+
+    int myPid;
+};