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>

src/editor/debug/graphHooks.ts

@@ -148,6 +148,30 @@ export function graphHooks({ state, editor }: HookContext) {
        */
       spectrum: () => ({ ...editor.eqEditor.curve.seen, taps: soundLibrary.spectrumTaps() }),
     },
+    /** The Compressor's tab (#378): its node, its numbers and knobs, and where to aim on the curve. */
+    compressor: {
+      shown: () => (editor.tab === 'compressor' ? editor.compressorEditor.shownFor : null),
+      numbers: () => editor.compressorEditor.numbers(),
+      /** Each knob's value, and whether it can be turned (a linked input greys it). */
+      knobs: () =>
+        Object.fromEntries(
+          Object.entries(editor.compressorEditor.knobs).map(([key, knob]) => [
+            key,
+            { value: knob.value, enabled: knob.enabled, field: knob.field.value },
+          ]),
+        ),
+      dialAt: (key: keyof typeof editor.compressorEditor.knobs) =>
+        editor.compressorEditor.knobs[key].dialGlobal(),
+      fieldAt: (key: keyof typeof editor.compressorEditor.knobs) =>
+        centreOf(editor.compressorEditor.knobs[key].field),
+      handleAt: (key: 'threshold' | 'ratio') => editor.compressorEditor.curve.handleGlobal(key),
+      pointAt: (inDb: number, outDb: number) => editor.compressorEditor.curve.pointGlobal(inDb, outDb),
+      /**
+       * The levels read so far (#378): how many readings with something coming in, the loudest on
+       * either side, the most taken away in one, and the taps as for the EQ.
+       */
+      levels: () => ({ ...editor.compressorEditor.seen, taps: soundLibrary.spectrumTaps() }),
+    },
     instrument: {
       current: () => editor.instrumentEditor.currentAssetId,
       info: () => editor.instrumentEditor.shownInfo,