Γ-W1-T3: staged contour traces draw the curve their exponent defines

New pure curve_tessellate joins the overlay's node vertices through curveMap,
one sample per pixel column; the knot no longer floats off its own trace.

src/shell/instrument/CMakeLists.txt

@@ -91,6 +91,7 @@ if(WIN32 AND EXISTS "${VST3_SDK}/public.sdk/source/main/pluginfactory.cpp")
         knob_deck deck_groups deck_values curve_popup spline_edit master_gain sample_usage
         bake_hold
         file_bytes curve_law stroke_aa
+        curve_tessellate
         bake_plan bake_render bake_reset bake_wire wav_codec)
     # SDK_INC gives the REAPER VST3 interfaces + API header for the bridge; WDL_INC gives
     # LICE for the editor. The VST3 SDK headers arrive via vst3_sdk PUBLIC.

src/shell/instrument/editor_paint_waveform.cpp

@@ -13,6 +13,7 @@
 #include <vector>
 
 #include "core/audio/peaks.h"                   // computeEnvelope (waveform binning)
+#include "core/instrument/ui/curve_tessellate.h"  // buildEnvelopeTrace (the staged trace)
 #include "core/instrument/ui/spline_edit.h"     // splineOverlayBox (the contour's mapping box)
 #include "core/instrument/ui/waveform_view.h"   // waveformSurface / laneEnvelope / frameToX
 #include "shell/instrument/editor_internal.h"   // kit adapters
@@ -212,17 +213,9 @@ void ReaSamplerEditor::paintEnvelopeOverlay(LICE_IBitmap* bmp, const OverlayArea
     const StageEnvelope env = packEnvelope(overlayEnv_, params_.play, frames, startFrame);
     const std::vector<EnvVertex> poly = buildEnvelopePolyline(env, waveArea, totalSeconds);
 
-    // Clip x to the wave rect. Knots are handles, not line vertices. Vertices stay INTEGER here
-    // — unlike the spline traces above — because they are the same positions the draggable
-    // handles are drawn at, and a sub-pixel trace would sit off its own handles.
     const LICE_pixel line = toLice(roleColor(Role::OverlayTrace));
     std::vector<ui::StrokePoint>& trace = scratchPoints();
-    trace.clear();
-    for (const EnvVertex& v : poly) {
-        if (v.knot) continue;
-        const int vx = (std::max)(area.x, (std::min)(area.right() - 1, v.x));
-        trace.push_back(ui::StrokePoint{static_cast<float>(vx), static_cast<float>(v.y)});
-    }
+    buildEnvelopeTrace(poly, env, area.x, area.right() - 1, trace);
     // A degenerate envelope (every stage collapsed to zero span) can reduce this to ONE vertex.
     // strokePolylineAA's round-cap zero-length case then draws a dot at it, marking the sole
     // point rather than drawing nothing — kept deliberately as more legible than a blank trace.