fix(mq_editor): apply coupled anchor drag to freqCurve in viewer canvas

Same P0↔P1 / P3↔P2 coupling as the amp editor, now for the frequency
bezier dragged in the main spectrogram viewer.

handoff(Claude): freq curve coupled drag fixed

1 files changed, 12 insertions, 1 deletions

diff --git a/tools/mq_editor/viewer.js b/tools/mq_editor/viewer.js
index 2575cac..c99d344 100644
--- a/tools/mq_editor/viewer.js
+++ b/tools/mq_editor/viewer.js
@@ -563,7 +563,13 @@ class SpectrogramViewer {
       if (this.selectedPartial >= 0 && this.selectedPartial < this.partials.length) {
         const ptIdx = this.hitTestControlPoint(x, y, this.partials[this.selectedPartial]);
         if (ptIdx >= 0) {
-          this.dragState = { pointIndex: ptIdx };
+          const curve = this.partials[this.selectedPartial].freqCurve;
+          let companionOff = null;
+          if (ptIdx === 0)
+            companionOff = { dt: curve.t1 - curve.t0, dv: curve.v1 - curve.v0 };
+          else if (ptIdx === 3)
+            companionOff = { dt: curve.t2 - curve.t3, dv: curve.v2 - curve.v3 };
+          this.dragState = { pointIndex: ptIdx, companionOff };
           canvas.style.cursor = 'grabbing';
           e.preventDefault();
           return;
@@ -585,6 +591,11 @@ class SpectrogramViewer {
         const i = this.dragState.pointIndex;
         partial.freqCurve['t' + i] = t;
         partial.freqCurve['v' + i] = v;
+        if (this.dragState.companionOff) {
+          const off = this.dragState.companionOff;
+          if (i === 0) { partial.freqCurve.t1 = t + off.dt; partial.freqCurve.v1 = v + off.dv; }
+          else          { partial.freqCurve.t2 = t + off.dt; partial.freqCurve.v2 = v + off.dv; }
+        }
         this.render();
         e.preventDefault();
         return;