A game that stays silent is only half a game, so a sound is an asset like any other (#45)

Sounds follow the road fonts already paved: the file goes to the server
content-addressed under its sha256, the project keeps a named asset that
points at it, and nothing is ever re-encoded. The format is read from the
file's own signature, not from what the browser claims - the same .m4a
arrives as audio/mp4, audio/x-m4a or as nothing at all.

Playing is two nodes. "Play sound" takes the asset and may raise or lower
its volume; every call is its own voice, so two jumps in a row are two
jumps heard. Its loop input is a choice of three - from the asset, on,
off - because a checkbox has to spend one of its two positions on "not
set" and would lose a case: an asset that loops could then never be
played once.

Below the graph core stays browser-free: NodeContext hands out an asset
id, BehaviorSystem resolves it against the project and folds the asset's
own volume and loop into the call, and only viewport/SoundLibrary knows
about Web Audio. A run without a sink plays nothing instead of throwing.

The CI browser is muted, so the ear is no witness: the debug hook counts
started and stopped voices, and step 34 reads that counter.

src/editor/debugHook.ts

@@ -7,9 +7,11 @@ import { effectiveScale, gameClock } from '../core/time';
 import { activeDrag, Button, isRendering, renderCount, requestRender, ui, Widget } from '../ui';
 import { particleLibrary } from '../viewport/ParticleLibrary';
 import { shaderLibrary } from '../viewport/ShaderLibrary';
+import { soundLibrary } from '../viewport/SoundLibrary';
 import { textureLibrary } from '../viewport/TextureLibrary';
 import type { CentreTab, Editor } from './Editor';
 import { currentFontPicker } from './font/FontPicker';
+import { currentSoundPicker } from './sound/SoundPicker';
 import { currentImagePicker } from './texture/ImagePicker';
 import type { EditorState } from './state';
 
@@ -361,6 +363,22 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
     /** The same for the font picker, whose rows are the preview. */
     fontPicker: () => currentFontPicker()?.debugInfo() ?? null,
     fontPickerRow: (file: string) => currentFontPicker()?.rowGlobal(file) ?? null,
+    /** And for the sound picker, whose rows carry a ▶ of their own. */
+    soundPicker: () => currentSoundPicker()?.debugInfo() ?? null,
+    soundPickerRow: (file: string) => currentSoundPicker()?.rowGlobal(file) ?? null,
+    soundPickerPlay: (file: string) => currentSoundPicker()?.playGlobal(file) ?? null,
+    /**
+     * Voices started, stopped and in flight. CI runs the browser with `--mute-audio`, so nothing
+     * is ever heard there: these counters are the only way a check can see that a graph played
+     * anything at all, the way `renderStats` is for a repaint that did not happen.
+     */
+    sound: {
+      stats: () => soundLibrary.stats(),
+      duration: (file: string) => soundLibrary.duration(file),
+      /** Decodes ahead of a check, so a play can be asserted without racing the network. */
+      load: (file: string) => soundLibrary.load(file).then((buffer) => buffer?.duration ?? null),
+      stopAll: () => soundLibrary.stopAll(),
+    },
     /** Which typeface a text ended up drawn in, and how wide it made it. */
     textInfo: (id: string) => viewport.textInfo(id),
     gameTextInfo: (id: string) => gameView.textInfo(id),