feat(vst): stand up VST3 instrument spike (S1) — skeleton, IPlugView↔LICE editor, REAPER bridge read

Vendor Steinberg VST3 SDK (v3.7.9_build_61); add reasampler_vst.vst3 as a second, additive build artifact with pure editor-geometry + bridge-marshal helpers under CTest.

src/vst/reasampler_processor.cpp

@@ -0,0 +1,82 @@
+// reasampler_processor.cpp — see reasampler_processor.h.
+
+#include "reasampler_processor.h"
+
+#include "pluginterfaces/vst/ivstaudioprocessor.h"
+#include "pluginterfaces/vst/vstspeaker.h"
+
+#include "reasampler_editor.h"
+
+using namespace Steinberg;
+using namespace Steinberg::Vst;
+
+namespace reasampler::vst {
+
+FUnknown* ReaSamplerProcessor::createInstance(void* /*context*/) {
+    // The host owns the returned reference. Cast up to the combined interface the SDK
+    // exposes (IAudioProcessor) so the FUnknown refcount is correctly rooted.
+    return static_cast<IAudioProcessor*>(new ReaSamplerProcessor());
+}
+
+tresult PLUGIN_API ReaSamplerProcessor::initialize(FUnknown* context) {
+    tresult result = SingleComponentEffect::initialize(context);
+    if (result != kResultOk) return result;
+
+    // Connect the REAPER bridge. Non-fatal if it fails (non-REAPER host): the
+    // instrument still loads, the editor just shows "no bridge".
+    bridge_.connect(context);
+
+    // Instrument bus topology: one event input (MIDI in, 16 channels), one stereo audio
+    // output, no audio input. This is the standard VSTi arrangement.
+    addEventInput(STR16("MIDI In"), 16);
+    addAudioOutput(STR16("Stereo Out"), SpeakerArr::kStereo);
+
+    return kResultOk;
+}
+
+tresult PLUGIN_API ReaSamplerProcessor::terminate() {
+    return SingleComponentEffect::terminate();
+}
+
+tresult PLUGIN_API ReaSamplerProcessor::setActive(TBool /*state*/) {
+    // Nothing to allocate/free in the silent skeleton; S4 will size voice buffers here
+    // against the setupProcessing block size.
+    return kResultOk;
+}
+
+tresult PLUGIN_API ReaSamplerProcessor::setupProcessing(ProcessSetup& setup) {
+    return SingleComponentEffect::setupProcessing(setup);
+}
+
+tresult PLUGIN_API ReaSamplerProcessor::process(ProcessData& data) {
+    // Silent skeleton: emit silence on the output bus so the instrument runs cleanly in
+    // REAPER's render/record path without a null buffer. S4 marshals MIDI->core->audio.
+    if (data.numOutputs > 0 && data.outputs && data.numSamples > 0) {
+        AudioBusBuffers& out = data.outputs[0];
+        for (int32 ch = 0; ch < out.numChannels; ++ch) {
+            if (data.symbolicSampleSize == kSample32) {
+                if (float* buf = out.channelBuffers32[ch]) {
+                    for (int32 i = 0; i < data.numSamples; ++i) buf[i] = 0.f;
+                }
+            } else if (data.symbolicSampleSize == kSample64) {
+                if (double* buf = out.channelBuffers64[ch]) {
+                    for (int32 i = 0; i < data.numSamples; ++i) buf[i] = 0.0;
+                }
+            }
+        }
+        // Flag output silence so the host can optimize (nothing plays yet).
+        out.silenceFlags = (out.numChannels >= 64)
+                               ? ~0ULL
+                               : ((1ULL << out.numChannels) - 1);
+    }
+    return kResultOk;
+}
+
+IPlugView* PLUGIN_API ReaSamplerProcessor::createView(FIDString name) {
+    if (name && FIDStringsEqual(name, ViewType::kEditor)) {
+        return new ReaSamplerEditor(&bridge_);
+    }
+    return nullptr;
+}
+
+}  // namespace reasampler::vst