phase4: Linux native_bridge build (Docker) — sfizz from source, --render SF2/SFZ

- Dockerfile: build sfizz tu native_bridge/sfizz-src (hoac git clone v1.2.3),
  sed fix sfizz.pc (-llibsfizz -> -lsfizz), cmake bridge voi 3 flag SMTG OFF
  (VSTGUI/plugin/hosting examples) — bridge headless chi can --render.
- CMakeLists: nhanh non-WIN32 build daw_vst_bridge tu main_linux.cpp +
  RenderJob.cpp + NativeInstrumentEngine.cpp (SF2/SF3 + SFZ; VST3/VST2
  hosting Windows-only, guard #ifdef _WIN32). gui_probe/plugin_host/
  seh_channel_test chi build tren Windows.
- RenderJob.cpp: JSON parser (sheredom json.h) khong con phu thuoc
  HAVE_VST3SDK — render SF2/SFZ chay duoc khong can VST3 SDK.
- NativeInstrumentEngine.cpp: guard windows.h/VST3/VST2/Sandbox/SEH.
- main.cpp: g_engine unconditional + guard disable_ime_contexts (_WIN32).
- engine.spec: bo pedalboard collect_dynamic_libs + hidden imports.
- vst_engine/render_engine: DecentSampler -> NotImplementedError + huong
  dan convert .dspreset -> .vstpreset; pianobook fallback synth.
- Verified: WSL Ubuntu 24.04 build OK, bridge Linux --render SF2 ra WAV
  44100 stereo peak 1575; Python tests 115 passed 1 skipped.
- Dockerfile build chua test duoc (may khong co Docker).

native_bridge/src/NativeInstrumentEngine.cpp

@@ -3,15 +3,19 @@
 
 #include <fluidsynth.h>
 #include <sfizz.hpp>
+#ifdef _WIN32
 #include "Vst3Instrument.h"
 #include "Vst2Instrument.h"
 #include "SandboxVst3Host.h"
+#endif
 
 // void* members keep fluid types out of the public header; cast here.
 #define FS_SYNTH (static_cast<fluid_synth_t*>(synth))
 #define FS_SETTINGS (static_cast<fluid_settings_t*>(settings))
 
+#ifdef _WIN32
 #include <windows.h>
+#endif
 
 #include <algorithm>
 #include <cctype>
@@ -168,6 +172,7 @@ std::unique_ptr<INativeInstrument> InstrumentEngineManager::create_instrument(In
     switch (type) {
         case InstrumentType::SOUNDFONT_SF2_SF3: return std::make_unique<FluidSynthInstrument>();
         case InstrumentType::SFZ:                return std::make_unique<SfizzInstrument>();
+#ifdef _WIN32
         case InstrumentType::VST3:
             // G4.2: SF_SANDBOX_VST3=1 -> host the VST3 in a child
             // process (plugin_host.exe). Crash kills only the child.
@@ -176,6 +181,13 @@ std::unique_ptr<INativeInstrument> InstrumentEngineManager::create_instrument(In
             return std::make_unique<Vst3Instrument>();
         case InstrumentType::VST2:
             return std::make_unique<Vst2Instrument>();
+#else
+        case InstrumentType::VST3:
+        case InstrumentType::VST2:
+            // Linux bridge: SF2/SF3 + SFZ only (Docker render). VST3/VST2
+            // hosting is Windows-only (COM/HWND/SHM realtime loop).
+            return nullptr;
+#endif
         default:                                 return nullptr;
     }
 }
@@ -191,6 +203,7 @@ bool InstrumentEngineManager::assign(uint32_t channel, InstrumentType type,
         loaded = static_cast<FluidSynthInstrument*>(inst.get())->loadSoundFontFile(path, sampleRate);
     else if (type == InstrumentType::SFZ)
         loaded = static_cast<SfizzInstrument*>(inst.get())->loadSfzFile(path, sampleRate);
+#ifdef _WIN32
     else if (type == InstrumentType::VST3) {
         if (auto* v = dynamic_cast<Vst3Instrument*>(inst.get()))
             loaded = v->loadPlugin(path, sampleRate);
@@ -207,6 +220,7 @@ bool InstrumentEngineManager::assign(uint32_t channel, InstrumentType type,
         if (auto* v = dynamic_cast<Vst3Instrument*>(inst.get()))
             v->setChannel(channel);
     }
+#endif
     if (!loaded) return false;
     // init() AFTER load: FluidSynth creates its synth inside loadSoundFontFile.
     if (!inst->init(sampleRate, blockSize)) return false;
@@ -415,8 +429,11 @@ static float* alignF(std::vector<float>& v, size_t n) {
 // (0xC0000005) is caught here — the channel is muted instead of killing the
 // whole bridge process. /EHa (set in CMakeLists) allows mixing with the
 // outer C++ try/catch net in main.cpp.
+#ifdef _WIN32
 static DWORD g_sehCode = 0;
 static void* g_sehAddr = nullptr;
+#endif
+#ifdef _WIN32
 static bool SafeProcessChannel(INativeInstrument* inst, float* outL, float* outR, uint32_t n, DWORD* outCode) {
     *outCode = 0;
     __try {
@@ -429,6 +446,18 @@ static bool SafeProcessChannel(INativeInstrument* inst, float* outL, float* outR
         return false;
     }
 }
+#else
+static bool SafeProcessChannel(INativeInstrument* inst, float* outL, float* outR, uint32_t n, uint32_t* outCode) {
+    *outCode = 0;
+    try {
+        inst->processAudioBlock(outL, outR, n);
+        return true;
+    } catch (...) {
+        *outCode = 1;
+        return false;
+    }
+}
+#endif
 
 void InstrumentEngineManager::renderAll(float* outputL, float* outputR, uint32_t numSamples) {
     if (isBypassed_.load()) {
@@ -446,11 +475,12 @@ void InstrumentEngineManager::renderAll(float* outputL, float* outputR, uint32_t
         float* spR = alignF(scratchR_, numSamples);
         std::memset(spL, 0, numSamples * sizeof(float));
         std::memset(spR, 0, numSamples * sizeof(float));
-        DWORD sehCode = 0;
+        uint32_t sehCode = 0;
         if (!SafeProcessChannel(inst.get(), spL, spR, numSamples, &sehCode)) {
             // G3.3: plugin fault — mute this channel only, keep the bridge up.
             if (!crashedCh_[ch]) {
                 crashedCh_[ch] = true;
+#ifdef _WIN32
                 {
                     HMODULE m = nullptr;
                     char mod[MAX_PATH] = "?";
@@ -477,6 +507,11 @@ void InstrumentEngineManager::renderAll(float* outputL, float* outputR, uint32_t
                     }
                     std::cerr << std::endl;
                 }
+#else
+                std::cerr << "[NativeBridge] G3.3: channel " << ch
+                          << " plugin crashed in processAudioBlock — muted until reload"
+                          << std::endl;
+#endif
             }
             continue;
         }