fix(v8): 5 bugs — orphan bridge watchdog+state overwrite, stuck-note stop race, white VST GUI retry, VSTi auto-load via saved plugin_path, track-header button overflow

- native bridge: dedicated watchdog thread (parent death / PID-reuse via GetProcessTimes) -> TerminateProcess self; transportStopped flag drops note-on after STOP + CC64 sustain release + allNotesOff on stop
- tauri: set_bridge_child overwrites managed BridgeProcess state (app.manage is no-op when state exists) so Destroyed handler kills restarted bridge
- ui: stopAllPlayback syncs isPlayingRef/subTabsRef + second transport stop at 150ms; onStatusChange resets __bridgeLoadedChannels at callback start (auto-restart never emits bridge-down); openVstGuiRetry waits for async C++ load before OPEN_GUI; loadVstToBridge uses synth_engine.plugin_path / listPlugins fallback and persists plugin_path on load; shrink track-header Synth/GUI buttons

native_bridge/src/main.cpp

@@ -209,6 +209,37 @@ int main(int argc, char* argv[]) {
     uint32_t parentPid = 0;
     if (const char* e = std::getenv("SF_PARENT_PID")) parentPid = (uint32_t)std::atoi(e);
 
+    // V8 bug 2: watchdog THREAD rieng - main loop chi check parent_alive giua
+    // cac block; neu VST process() chan loop thi khong bao gio thoat -> orphan.
+    // Thread nay chay doc lap, parent chet -> TerminateProcess ngay. Kem
+    // start-time check chong PID reuse (OpenProcess tra handle cua process
+    // khac chiem lai PID -> tuong parent con song mai).
+    if (parentPid != 0) {
+        std::thread([parentPid]() {
+            auto proc_birth = [](HANDLE h) -> uint64_t {
+                FILETIME c, e, k, u;
+                if (GetProcessTimes(h, &c, &e, &k, &u))
+                    return (uint64_t(c.dwHighDateTime) << 32) | c.dwLowDateTime;
+                return 0;
+            };
+            uint64_t birth = 0;
+            {
+                HANDLE h = OpenProcess(PROCESS_QUERY_LIMITED_INFORMATION, FALSE, parentPid);
+                if (h) { birth = proc_birth(h); CloseHandle(h); }
+            }
+            for (;;) {
+                Sleep(2000);
+                HANDLE h = OpenProcess(PROCESS_QUERY_LIMITED_INFORMATION, FALSE, parentPid);
+                if (!h) { TerminateProcess(GetCurrentProcess(), 0); return; }
+                uint64_t nowBirth = proc_birth(h);
+                CloseHandle(h);
+                if (birth != 0 && nowBirth != 0 && nowBirth != birth) {
+                    TerminateProcess(GetCurrentProcess(), 0); return;
+                }
+            }
+        }).detach();
+    }
+
 #ifdef _WIN32
     // Real-time-ish timing: 1ms scheduler resolution
     timeBeginPeriod(1);
@@ -252,6 +283,10 @@ int main(int argc, char* argv[]) {
     }
     const uint32_t block = AUDIO_BLOCK_SIZE;
     uint64_t playheadSamples = 0;
+    // V8 bug 3: khi STOP da xu ly, bo qua NOTE_ON (velocity>0) den sau - JS
+    // note-on timer co the bay toi sau STOP (guardPlay tre do React re-render)
+    // -> retrigger note -> VST loop am. Chi PLAY moi nhan note-on lai.
+    bool transportStopped = false;
 
     auto dispatch = [&](const SharedAudioBufferIPC::MidiEventIPC& evt) {
         auto* inst = instruments.get(evt.channel);
@@ -261,9 +296,10 @@ int main(int argc, char* argv[]) {
                 // sampleOffset LUON LUON = 0 khi den day: events duoc dispatch ngay
                 // truoc segment chua no (A11 splitting), nen offset tuong doi la 0.
                 // Truyen offset tuyet doi truoc day lam sfizz/VST3 trigger tre.
-                if (evt.velocity > 0)
+                if (evt.velocity > 0) {
+                    if (transportStopped) return; // V8 bug 3: drop note-on sau STOP
                     inst->noteOn(evt.channel, evt.pitch, evt.velocity / 127.0f, 0);
-                else
+                } else
                     inst->noteOff(evt.channel, evt.pitch, 0);
                 break;
             case 0x8:
@@ -363,9 +399,17 @@ int main(int argc, char* argv[]) {
                 std::cout << "[NativeBridge] PANIC — all notes off" << std::endl;
             } else if (c.type == 3) { // TRANSPORT (A13)
                 if (c.arg0 == 0) { // STOP → flush every note immediately
+                    transportStopped = true;
+                    // Release sustain pedal TRUOC (CC64=0) — nhieu VSTi giu note
+                    // khi pedal con down -> note-off cua allNotesOff bi bo qua
+                    // -> am treo loop (V8 bug 3).
+                    for (uint32_t ch = 0; ch < 16; ++ch) {
+                        if (auto* inst = instruments.get(ch)) inst->controlChange(ch, 64, 0);
+                    }
                     instruments.allNotesOff();
                     std::cout << "[NativeBridge] transport STOP — all notes off" << std::endl;
                 } else if (c.arg0 == 1) { // PLAY
+                    transportStopped = false;
                     playheadSamples = c.arg1;
                     std::cout << "[NativeBridge] transport PLAY playhead=" << playheadSamples << std::endl;
                 } else if (c.arg0 == 2) { // SET_POSITION (seek while stopped)