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/PlaySession.ts

@@ -16,6 +16,7 @@ import { gameClock } from '../core/time';
 import { Input } from '../runtime/systems/Input';
 import { World } from '../runtime/World';
 import { ui } from '../ui';
+import { soundLibrary } from '../viewport/SoundLibrary';
 import type { GameViewport } from './viewport/GameViewport';
 import type { GraphEditor } from './graph/GraphEditor';
 import type { LiveMachineState } from './graph/GraphCanvas';
@@ -72,6 +73,9 @@ export class PlaySession {
   togglePause(): void {
     if (!this.world) return;
     this.state.setPaused(!this.state.paused);
+    // A held note is part of the picture a pause freezes: the sounds stop where they are and carry
+    // on mid-note, rather than playing to their end over a still image.
+    soundLibrary.setSuspended(this.state.paused);
     ui().focus.blur();
     this.state.setNotice(this.playNotice(), 'quiet');
   }
@@ -109,7 +113,7 @@ export class PlaySession {
     const world = World.instantiate(runtime, scene.id);
     this.world = world;
     this.input.attach();
-    this.behaviors = addGameSystems(world, runtime, this.input);
+    this.behaviors = addGameSystems(world, runtime, this.input, undefined, soundLibrary);
     this.host.gameView.setWorld(world);
     this.host.showGame();
     this.state.setNotice(this.playNotice(), 'quiet');
@@ -126,6 +130,9 @@ export class PlaySession {
   stop(): void {
     // The run's seconds end with it: the editor goes back to the picture of a freshly loaded scene.
     gameClock.reset();
+    // And its sounds end with it, looping music included – nothing may outlive the world.
+    soundLibrary.setSuspended(false);
+    soundLibrary.stopAll();
     const world = this.world;
     this.world = null;
     this.behaviors = null;