feat(mq_editor): peaks display, STFT cache refactor, threshold reactivity

- STFTCache: cache squaredAmplitude (re²+im²) per frame, add getSquaredAmplitude(t)
- getMagnitudeDB uses cached sq amp (10*log10, no sqrt)
- detectPeaks uses squaredAmp from cache instead of recomputing FFT
- extractPartials: use cache frames, return {partials, frames}
- Press 'p' to toggle raw peak overlay in viewer
- threshold input: step=any, change event triggers re-extraction
- runExtraction() shared by button and threshold change

handoff(Claude): mq_partial peaks/cache refactor complete

1 files changed, 37 insertions, 0 deletions

diff --git a/tools/mq_editor/viewer.js b/tools/mq_editor/viewer.js
index c57d693..5065498 100644
--- a/tools/mq_editor/viewer.js
+++ b/tools/mq_editor/viewer.js
@@ -8,6 +8,8 @@ class SpectrogramViewer {
     this.audioBuffer = audioBuffer;
     this.stftCache = stftCache;
     this.partials = [];
+    this.frames = [];
+    this.showPeaks = false;
 
     // Fixed time bounds
     this.t_min = 0;
@@ -57,6 +59,15 @@ class SpectrogramViewer {
     this.render();
   }
 
+  setFrames(frames) {
+    this.frames = frames;
+  }
+
+  togglePeaks() {
+    this.showPeaks = !this.showPeaks;
+    this.render();
+  }
+
   reset() {
     this.zoom_factor = 1.0;
     this.t_center = this.audioBuffer.duration / 2;
@@ -94,6 +105,7 @@ class SpectrogramViewer {
 
   render() {
     this.renderSpectrogram();
+    if (this.showPeaks) this.renderPeaks();
     this.renderPartials();
     this.drawAxes();
     this.drawPlayhead();
@@ -271,6 +283,31 @@ class SpectrogramViewer {
     }
   }
 
+  // Render raw peaks from mq_extract (before partial tracking)
+  renderPeaks() {
+    const {ctx, canvas, frames} = this;
+    if (!frames || frames.length === 0) return;
+
+    const timeDuration = this.t_view_max - this.t_view_min;
+    const freqRange = this.freqEnd - this.freqStart;
+
+    ctx.fillStyle = '#fff';
+
+    for (const frame of frames) {
+      const t = frame.time;
+      if (t < this.t_view_min || t > this.t_view_max) continue;
+
+      const x = (t - this.t_view_min) / timeDuration * canvas.width;
+
+      for (const peak of frame.peaks) {
+        if (peak.freq < this.freqStart || peak.freq > this.freqEnd) continue;
+
+        const y = canvas.height - (peak.freq - this.freqStart) / freqRange * canvas.height;
+        ctx.fillRect(x - 1, y - 1, 3, 3);
+      }
+    }
+  }
+
   // Draw control point
   drawControlPoint(t, v) {
     if (t < this.t_view_min || t > this.t_view_max) return;