S7: stereo channel mode — core channel dimension, v4 mode state, VST3 bus negotiation, editor toggle

Per-instance mono|stereo (default mono, byte-identical). Stereo grows SampleData a 2nd
channel + a per-channel VoiceEngine render; decodeChannels applies the cross-mode policy;
setBusArrangements pins the mode's arrangement and restartComponent(kIoChanged) re-negotiates.

src/vst/reasampler_editor.cpp

@@ -146,6 +146,7 @@ void ReaSamplerEditor::refreshFromBank() {
     banks_ = banksJson ? listBanks(*banksJson) : std::vector<BankChoice>{};
     selectedId_ = processor_->selectedSampleId();
     map_ = processor_->performanceMap();
+    channelMode_ = processor_->channelMode();
     if (selectedZone_ >= static_cast<int>(map_.zones.size())) selectedZone_ = -1;
     // Drop a filter that names a bank no longer present.
     if (!activeFilterBankId_.empty()) {
@@ -334,6 +335,22 @@ Rect zonesStripArea(const EditorBands& bands) {
     return Rect{bands.content.left + pad, stripTop, bands.content.right - pad,
                 stripTop + kStripBandHeight};
 }
+
+// The S7 mono/stereo toggle, a two-segment control anchored to the RIGHT of the setup band's
+// header row (same y as the sample-name header, so it reads as "this capture's output mode").
+// `area` is the full setup Rect. Returns {mono-segment, stereo-segment}; each is kSegW wide,
+// kSegH tall, side by side. Kept to a small fenced block (S11 owns the waveform region).
+constexpr int kChanSegW = 52;
+constexpr int kChanSegH = 18;
+struct ChannelToggleRects { Rect mono; Rect stereo; };
+ChannelToggleRects channelToggleRects(const Rect& area) {
+    constexpr int pad = 8;
+    const int top = area.top + 4;
+    const int right = area.right - pad;
+    const Rect stereo{right - kChanSegW, top, right, top + kChanSegH};
+    const Rect mono{stereo.left - kChanSegW, top, stereo.left, top + kChanSegH};
+    return {mono, stereo};
+}
 }  // namespace
 
 void ReaSamplerEditor::paint(HDC hdc) {
@@ -477,10 +494,22 @@ void ReaSamplerEditor::paintSetup(LICE_IBitmap* bmp, const Rect& area) {
     }
 
     const int pad = 8;
-    Rect headerR{area.left + pad, area.top + 4, area.right - pad, area.top + 22};
+    // The mono/stereo toggle sits at the right of the header row; keep the name text clear of it.
+    const ChannelToggleRects chan = channelToggleRects(area);
+    Rect headerR{area.left + pad, area.top + 4, chan.mono.left - 8, area.top + 22};
     std::string header = sampleLabel(samples_, selectedId_) + "   root " + noteLabel(root);
     drawText(bmp, headerR, header.c_str(), kRgbText);
 
+    // S7 mono | stereo output-mode toggle. The active segment highlights (kColTabActiveBg),
+    // the inactive is kColTabBg — the same visual grammar as the Browser/Zones toggle.
+    const bool isStereo = (channelMode_ == ChannelMode::Stereo);
+    LICE_FillRect(bmp, chan.mono.left, chan.mono.top, chan.mono.width(), chan.mono.height(),
+                  isStereo ? kColTabBg : kColTabActiveBg, 1.0f, 0);
+    LICE_FillRect(bmp, chan.stereo.left, chan.stereo.top, chan.stereo.width(),
+                  chan.stereo.height(), isStereo ? kColTabActiveBg : kColTabBg, 1.0f, 0);
+    drawTextCentered(bmp, chan.mono, "Mono", kRgbText);
+    drawTextCentered(bmp, chan.stereo, "Stereo", kRgbText);
+
     Rect hintR{area.left + pad, headerR.bottom, area.right - pad, headerR.bottom + 16};
     drawText(bmp, hintR, "Drag on the keyboard to set the root note.", kRgbDim);
 
@@ -597,9 +626,25 @@ void ReaSamplerEditor::onMouseDown(int x, int y) {
             commitAndReload();  // publishes the pick + reloads; process() plays it repitched
             return;
         }
-        // The setup strip: grab the root marker (drag to set the picked capture's root).
+        // The setup band: the mono/stereo toggle (header row), then the root-marker strip.
         if (havePick) {
             const Rect area{bands.content.left, setupTop, bands.content.right, bands.content.bottom};
+            // S7: a click on a channel-mode segment sets the instance mode (setChannelMode
+            // re-negotiates the bus + reloads; a no-op set for the already-active mode is ignored
+            // by the processor). Snapshot the new mode locally so the paint reflects it at once.
+            const ChannelToggleRects chan = channelToggleRects(area);
+            if (contains(chan.mono, x, y)) {
+                channelMode_ = ChannelMode::Mono;
+                processor_->setChannelMode(ChannelMode::Mono);
+                invalidate();
+                return;
+            }
+            if (contains(chan.stereo, x, y)) {
+                channelMode_ = ChannelMode::Stereo;
+                processor_->setChannelMode(ChannelMode::Stereo);
+                invalidate();
+                return;
+            }
             const Rect stripArea = setupStripArea(area);
             const StripLayout sl = layoutStrip(stripArea.width(), stripArea.height());
             const int note = keyAtPoint(sl, x - stripArea.left, y - stripArea.top);