Change the sound FX parameters of a sound while it plays #315

Until now a value handed to a sound FX counted from the start of the
voice only. An engine whose pitch follows the speed, or a loop that
gets quieter, could not be built. Every play of Play sound now gives
out the number of its voice, and a new node lets the knobs of that one
voice glide to new values while it plays.

- Play sound has a new output voice: the number of this one play, or 0
  where nothing was played. Kept in a Number variable it reaches the
  voice from another event. Two plays of one sound are two voices.
- New action node Set sound FX parameters (exec, voice, fx params).
  It reaches exactly the voice it is given, a detached one too. A
  voice that has ended, or voice 0, is not reached.
- AudioSink.play returns the voice number and takes the plan and the
  values (FxVoice) instead of a finished chain. AudioSink.tune takes a
  voice number and new values. A name the voice's FX does not have is
  left out, one not given keeps its value.
- SoundLibrary hands out the number at once, before the bytes are
  there, and never twice. A voice still waiting for its bytes starts
  with the values handed in meanwhile.
- Every knob of a voice moves with setTargetAtTime (30 ms time
  constant). A knob whose value did not change is not sent again, so a
  tune every frame costs next to nothing.
- A pitch on a playing voice glides by playbackRate. A new WSOLA copy
  in the middle of a sound is not worked out, so the voice gets shorter
  or longer while it is moved. On a loop that is not heard.
- fxChainOf now gives a chain whose shape depends on the plan alone.
  A stage fed by a parameter stays at 0 dB, and a Mix fed by a
  parameter keeps both ways. A typed-in 0 or Mix at 0/1 is still left
  out by the compiler.
- Every way of a voice has a source of its own, also at the same
  pitch, so each can glide on its own. The pitched copy is shared.
- The tab keeps the numbers of what it plays, so moving a parameter
  field is heard at once.
- Test hook __gm.sound.levels(file) reads the knobs of every voice of
  a file, oldest first, and stats() counts the voices tuned.

Tests:
- soundfx.test.ts: 29 tests (+2 for the node in a running world: the
  voice of the first of two plays of one sound, and a play that played
  nothing)
- sound-library.test.ts: 15 tests (+3: glide, reach by number,
  pending voice)
- node-catalog.test.ts: 370 tests (+2, Play sound checks its voice)
- sounds + keep-on-scene-load: 31 tests, unchanged
- Counter-test: a tune that reaches every voice of the same file makes
  the reach test fail.
- e2e 34 (melektaus-atx): ALL PASSED - 30 checks (+1). In Chrome two
  looping voices of one sound start at depth 7. The one whose number
  sits in a variable glides to 0.7938 (2^(-4/12) = 0.7937), the other
  stays at 1. Both gains stay at 0.5012.
- The gate ran before voices got a number (CHECK EXIT 0, 241 files,
  3658 tests), not after.

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

src/core/graph/nodes/data/SoundFxParameters.ts

@@ -6,14 +6,14 @@ import { asNumber } from '../../values';
 /**
  * Values for the parameters of one sound FX (#311), picked from those its Input declares the way a
  * Variables node picks variables. Each picked one is a number input starting at the FX's default;
- * the bundle goes into the `fx params` input of a `Play sound`.
+ * the bundle goes into the `fx params` input of a `Play sound` or a `Set sound FX parameters`.
  */
 export const SoundFxParameters: NodeDef = {
   type: SOUND_FX_PARAMETERS,
   label: 'Sound FX parameters',
   category: 'data',
   description:
-    'Values for the parameters of a sound FX, for the "fx params" input of a Play sound. Pick the parameters to set; one not picked keeps the default its Input gives it.',
+    'Values for the parameters of a sound FX, for the "fx params" input of a Play sound or a Set sound FX parameters. Pick the parameters to set; one not picked keeps the default its Input gives it, or on a playing sound the value it has.',
   inputs: [],
   outputs: [{ key: 'params', label: 'params', type: 'fxparams' }],
   params: [SOUND_FX_SETTING],