Edit a Compressor in a tab of its own, with knobs and levels (#378)

A Compressor had only its number rows in the node. Its numbers are
easier to set by feel on a dial, and what it does is easier to judge
when the level going in and the level going out are seen side by side.

- Knob is a new widget in the toolkit: a slider bent into a circle,
  its name above and a number field below. A drag up or down turns
  it, Shift a tenth as far, a notch of the wheel a fiftieth of the
  turn, a double-click sets the default, the number takes a typed
  value. A taper gives the low end more of the turn.
- The Compressor's tab opens on a double-click, one per node, like
  the Parametric EQ's. It has a knob for each of the seven numbers,
  greyed while its input is linked.
- Its curve shows level in to level out from -60 to 0 dB. The point
  where it bends sets the threshold, the end of the curve sets the
  ratio that ends there.
- Its levels show the last 4 s on both sides of the node. Where it
  takes more than 0.5 dB away, the stretch below the level coming in
  is tinted. The makeup is left out of that.
- The Compressor is tapped like the EQ. SpectrumTaps listens to more
  than one node at once and reads the loudest sample of the last
  25 ms on each side.
- The node tabs share one map in the editor (nodeTabs), so a third
  kind needs no new plumbing.

Findings:

- CI task 614 for 23922ee was red on the memory check of the stream:
  the tab's renderer grew by 94 MB with nothing decoded. Play mode
  made garbage of its own and was read before a collection. Both
  readings in play now come after one, and the check compares the
  growth streamed with the growth decoded (3.7 MB against 59.8 MB).
- The ratio handle sat on the right edge of the picture, where a
  widget's hit area ends. The curve is inset by the grab radius.

Tests:

- Gate (melektaus-atx): 282 files, 4338 tests (17 new)
- e2e 34 (melektaus-atx): ALL PASSED, 116 checks (6 new)
- Counter-checks: an inverted ratio search, stop() letting go of
  every node and a drag without its least step each fail exactly
  their test.
- Looked at the tab in a screenshot: a blip at -4.4 dB came out at
  -16.7 dB, the gap tinted, the threshold line at -24.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/viewport/spectrum.test.ts

@@ -23,6 +23,12 @@ class FakeNode {
   getFloatFrequencyData(data: Float32Array): void {
     data.fill(this.context.made.length);
   }
+  /** What the analyser heard last: `wave`, at the end of `data` like the newest samples. */
+  wave: number[] = [];
+  getFloatTimeDomainData(data: Float32Array): void {
+    data.fill(0);
+    data.set(this.wave, data.length - this.wave.length);
+  }
 }
 
 class FakeContext {
@@ -50,7 +56,7 @@ describe('the taps of the spectrum', () => {
     taps.hold(tap('fx:eq', 'in'), new FakeNode(context) as never);
     expect(taps.info()).toEqual({ listened: '', held: 1, feeding: 0 });
     expect(context.made).toHaveLength(0);
-    expect(taps.read()).toBeNull();
+    expect(taps.read('fx:eq')).toBeNull();
   });
 
   it('feed the analyser of their side while listened to, a voice started before as well', () => {
@@ -69,7 +75,7 @@ describe('the taps of the spectrum', () => {
     expect([...before.links]).toEqual([sumIn]);
     expect([...after.links]).toEqual([sumOut]);
     expect(other.links.size).toBe(0);
-    expect(taps.read()?.binHz).toBeCloseTo(48000 / 8192, 9);
+    expect(taps.read('fx:eq')?.binHz).toBeCloseTo(48000 / 8192, 9);
   });
 
   it('let go of the analysers once nobody listens, or once the voice stops', () => {
@@ -87,6 +93,41 @@ describe('the taps of the spectrum', () => {
     taps.stop();
     expect(bus.links.size).toBe(0);
     expect(taps.info()).toEqual({ listened: '', held: 1, feeding: 0 });
-    expect(taps.read()).toBeNull();
+    expect(taps.read('fx:eq')).toBeNull();
+  });
+
+  it('listen to two nodes at once, and let one go without the other (#378)', () => {
+    const context = new FakeContext();
+    const taps = new SpectrumTaps();
+    const eq = new FakeNode(context);
+    const compressor = new FakeNode(context);
+    taps.hold(tap('fx:eq', 'in'), eq as never);
+    taps.hold(tap('fx:comp', 'in'), compressor as never);
+    taps.listen('fx:eq');
+    taps.listen('fx:comp');
+    expect(taps.info()).toEqual({ listened: 'fx:eq fx:comp', held: 2, feeding: 2 });
+    expect(eq.links.size).toBe(1);
+    expect(compressor.links.size).toBe(1);
+    taps.stop('fx:eq');
+    expect(eq.links.size).toBe(0);
+    expect(compressor.links.size).toBe(1);
+    expect(taps.info()).toEqual({ listened: 'fx:comp', held: 2, feeding: 1 });
+    expect(taps.read('fx:comp')).not.toBeNull();
+  });
+
+  it('give the loudest sample of the last stretch on each side, in dB (#378)', () => {
+    const context = new FakeContext();
+    const taps = new SpectrumTaps();
+    expect(taps.levels('fx:comp', 0.01)).toBeNull();
+    taps.listen('fx:comp');
+    taps.hold(tap('fx:comp', 'in'), new FakeNode(context) as never);
+    const [, analyserIn, , analyserOut] = context.made;
+    // A peak of 1 long ago, then 0.5: a window of 10 ms (480 samples) only sees the 0.5.
+    analyserIn!.wave = [1, ...new Array<number>(1000).fill(0), -0.5, 0.25];
+    analyserOut!.wave = [];
+    const levels = taps.levels('fx:comp', 0.01);
+    expect(levels?.in).toBeCloseTo(20 * Math.log10(0.5), 9);
+    expect(levels?.out).toBe(-Infinity);
+    expect(taps.levels('fx:comp', 1)?.in).toBeCloseTo(0, 9);
   });
 });