Show a Limiter node as a device that holds what it took away (#397)

A Limiter only said what it does in rows of numbers. How much it took
away, and when, could not be seen at all, and a short sound is over
before any needle could show it. Now the node is a device of its own
size, and its screen catches the reduction from the moment a sound
starts and holds it once the sound ends.

- LimiterPanel draws a 720x280 plate of brushed brick. The threshold
  knob is large, ceiling and release are small beside it, auto-gain is
  a lever. A LIMIT lamp lights while it takes something away.
- The screen hangs the reduction down from the top, 0 to 24 dB by the
  square root like the Compressor's meter. The level coming in runs
  along the bottom, orange above the limit. Time runs from the start
  of the sound over 1, 2, 4 or 8 s, and a longer sound rolls.
- ReductionCapture in limiterView holds the capture after 0.4 s of
  silence, without the silence, until the next sound. It writes the
  most taken away and when, and NOW or LASTED on the right.
- The Limiter is tapped now, like the Compressor. The face reads the
  loudest sample since the last frame on both sides.
- SpectrumTaps.levels takes a lateBy. The side in front is read 5 ms
  earlier, so a peak going in is met by what it became.
- limiterReduction leaves the auto-gain out and solves Wet's blend for
  the limited part. Less than 0.2 dB counts as none.
- A capture is also held when the node leaves the picture. Changing a
  knob or the lever leaves it as it is.
- Hook __gm.limiter.panel(id) for the sound FX and instrument graphs.

Decided myself:

- The capture stays held until the next sound, not for a fixed time.
- The screen has no wet knob, as the Compressor's has none.
- The Limiter's two taps cost two gains of 1 per voice. The analysers
  only exist while the node is in the picture.

Measured on stein2: the seeded blip at -4.4 dBFS against -12 dB showed
7.56 dB. Three hits at 0, -8 and -2 dBFS showed 11.9 dB at the first.
In e2e 34 on melektaus-atx, -10.44 dBFS in against -20 dB showed
9.56 dB, the difference to the hundredth.

Tests:
- Unit: limiter-view 13 tests (new), spectrum 6 (1 new), soundfx 67
  with the Limiter's taps.
- Counter-test: without Wet's share in the formula the blend test
  fails.
- e2e 34: ALL PASSED, 138 checks (1 new).
- Gate: CHECK EXIT 0, 290 files, 4445 tests.

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

tools/e2e/34-sound.mjs

@@ -1495,6 +1495,65 @@ export async function sound(t) {
   await mutate(`
     const graph = __gm.state.project.assets.find((a) => a.id === ${JSON.stringify(fxId)}).graph;
     graph.nodes = graph.nodes.filter((n) => n.id !== 'fx-st');`);
+  // #397: a Limiter is a device of its own size whose screen catches what it takes away from the
+  //       moment a sound starts and holds it once the sound ends. Wired in before the output, the
+  //       most it caught is the loudest that came in over its limit. The lever and the threshold
+  //       knob are one undo step each and leave the capture held.
+  await mutate(`
+    const graph = __gm.state.project.assets.find((a) => a.id === ${JSON.stringify(fxId)}).graph;
+    graph.nodes.push(${JSON.stringify(node('fx-lm', 'SoundFxLimiter', 0, 400, { threshold: -20 }))});
+    const last = graph.edges.find((e) => e.to.node === 'fx-out' && e.to.port === 'in');
+    graph.edges.push({ id: 'fx-e-lm', from: { node: 'fx-lm', port: 'out' }, to: { node: 'fx-out', port: 'in' } });
+    last.to = { node: 'fx-lm', port: 'in' };`);
+  await evaluate('__gm.soundfx.fit()');
+  await sleep(100);
+  const lmPanel = () => json("__gm.limiter.panel('fx-lm')");
+  const lmShown = await lmPanel();
+  await evaluate('__gm.sound.stopAll()');
+  await evaluate('__gm.soundfx.play()');
+  const lmHeld = await waitFor(lmPanel, (p) => p.scope.state === 'held', 40);
+  await click(lmShown.autoGain.at.x, lmShown.autoGain.at.y);
+  const lmOff = { params: await knobParams('fx-lm'), panel: await lmPanel() };
+  const lmDial = lmShown.knobs.threshold.dial;
+  await drag(lmDial.x, lmDial.y, lmDial.x, lmDial.y - 20);
+  const lmTurned = (await knobParams('fx-lm')).threshold;
+  for (let i = 0; i < 2; i++) await press('z', { ctrl: true });
+  const lmUndone = { params: await knobParams('fx-lm'), panel: await lmPanel() };
+  check(
+    'a Limiter node holds what it took away once the sound ends, the most of it the loudest over its limit; its lever and threshold are one undo step each',
+    lmShown.size.w === 720 &&
+      lmShown.size.h === 280 &&
+      Object.values(lmShown.inputs).length === 5 &&
+      Object.values(lmShown.inputs).every((p) => p.x < lmShown.rect.x) &&
+      Object.values(lmShown.outputs).every((p) => p.x > lmShown.rect.x + lmShown.rect.w) &&
+      lmShown.knobs.threshold.number === '-20 dB' &&
+      lmShown.autoGain.lit &&
+      lmShown.autoGain.says === '+19 dB' &&
+      lmShown.status === 'WAITING FOR SOUND' &&
+      lmHeld.status === 'HELD' &&
+      lmHeld.scope.limited > 0 &&
+      lmHeld.scope.most !== null &&
+      lmHeld.scope.loudest > -20 &&
+      Math.abs(lmHeld.scope.most.db - (lmHeld.scope.loudest + 20)) < 1 &&
+      /^MOST -\d+(\.\d)? dB AT \d+ ms$/.test(lmHeld.scope.says.most) &&
+      lmHeld.scope.says.side.startsWith('LASTED ') &&
+      !lmHeld.lamp &&
+      lmOff.params.autoGain === false &&
+      lmOff.panel.autoGain.says === 'off' &&
+      lmOff.panel.scope.state === 'held' &&
+      lmTurned > -20 &&
+      lmUndone.params.threshold === -20 &&
+      lmUndone.params.autoGain !== false &&
+      lmUndone.panel.scope.state === 'held' &&
+      lmUndone.panel.scope.most?.db === lmHeld.scope.most.db,
+    JSON.stringify({ lmShown, lmHeld, lmOff, lmTurned, lmUndone }),
+  );
+  await mutate(`
+    const graph = __gm.state.project.assets.find((a) => a.id === ${JSON.stringify(fxId)}).graph;
+    const into = graph.edges.find((e) => e.to.node === 'fx-lm' && e.to.port === 'in');
+    into.to = { node: 'fx-out', port: 'in' };
+    graph.edges = graph.edges.filter((e) => e.id !== 'fx-e-lm');
+    graph.nodes = graph.nodes.filter((n) => n.id !== 'fx-lm');`);
   await showTab('scene');
   await mutate(`
     const graph = __gm.state.project.assets.find((a) => a.id === 'sn-logic').graph;