G4.2: bridge-side plugin process pool — SandboxVst3Host spawns/respawns plugin_host.exe per channel, MIDI forward + audio snapshot + watchdog mute/respawn, crash isolation verified

native_bridge/include/SandboxVst3Host.h

@@ -0,0 +1,58 @@
+// native_bridge/include/SandboxVst3Host.h
+// G4.2: VST3 instrument hosted in a CHILD PROCESS (plugin_host.exe). The
+// plugin's crash kills only the child; this host mutes the channel, respawns
+// the child, and the bridge + other channels keep running. MIDI flows bridge
+// -> child SHM (midiQueue), audio flows child -> bridge (masterLeft/Right).
+#ifndef SANDBOX_VST3_HOST_H
+#define SANDBOX_VST3_HOST_H
+
+#include "INativeInstrument.h"
+#include "SharedMemoryIPC.h"
+
+#include <atomic>
+#include <string>
+#include <thread>
+
+#ifdef _WIN32
+#include <windows.h>
+#endif
+
+class SandboxVst3Host : public INativeInstrument {
+public:
+    SandboxVst3Host();
+    ~SandboxVst3Host() override;
+
+    bool loadPlugin(const std::string& path, double sampleRate, uint32_t channel);
+
+    bool init(double sampleRate, uint32_t maxBlockSize) override;
+    void selectProgram(uint32_t channel, uint32_t bank, uint32_t program) override {}
+    void noteOn(uint32_t channel, uint32_t pitch, float velocity, uint32_t sampleOffset) override;
+    void noteOff(uint32_t channel, uint32_t pitch, uint32_t sampleOffset) override;
+    void controlChange(uint32_t channel, uint32_t cc, uint32_t value) override;
+    void programChange(uint32_t channel, uint32_t program) override;
+    void pitchBend(uint32_t channel, uint32_t bend14) override;
+    // The child owns its GUI window (plugin_host opens it on its main thread).
+    bool openGUI(void* parentWindowHandle) override { (void)parentWindowHandle; return true; }
+    void closeGUI() override {}  // child window dies with the child process
+    void processAudioBlock(float* outputL, float* outputR, uint32_t numSamples) override;
+
+private:
+    bool spawnChild();
+    void watchdogLoop();
+
+    std::string path_;
+    std::string shmName_;
+    double sampleRate_ = 44100.0;
+    uint32_t block_ = AUDIO_BLOCK_SIZE;
+    uint32_t channel_ = 0;
+    ShmHandle* shm_ = nullptr;
+    SharedAudioBufferIPC* ipc_ = nullptr;
+    std::atomic<bool> alive_{false};
+    std::atomic<bool> stop_{false};
+    std::thread watchdog_;
+#ifdef _WIN32
+    HANDLE childProc_ = nullptr;
+#endif
+};
+
+#endif // SANDBOX_VST3_HOST_H

native_bridge/include/SharedMemoryIPC.h

@@ -69,3 +69,6 @@ ShmHandle* shm_open(const char* name);
 ShmHandle* shm_create(const char* name);
 SharedAudioBufferIPC* shm_ptr(ShmHandle* h);
 void shm_close(ShmHandle* h);
+bool shm_write_midi(ShmHandle* h, uint8_t cmd, uint8_t channel, uint8_t pitch,
+                    uint8_t velocity, uint32_t sampleOffset, uint8_t data2 = 0,
+                    uint8_t data3 = 0);