Route sounds, songs and buses in one Master routing graph (#351)

A project bus could only go into one other bus, and a sound, an
instrument, a pattern or a song into exactly one bus. A shared reverb
needs a sound to go there in part and on dry at the same time. Instead
of a list of sends on every asset, the project gets one routing graph
like the routing of a song (#350), one level up.

- Menu -> Master routing opens a tab with one graph per project. It has
  a node per sound, instrument, pattern, song and bus, named after its
  asset, and one Master. Embedded assets have none, their song routes
  them.
- The nodes follow the assets. Every edit settles the routing in the
  same undo step (KeepRoutingCommand), so an undone delete brings the
  links of its asset back. A new asset gets a node and a link to the
  master. What went only into a deleted bus goes to the master.
- New nodes start in three columns: what plays, the buses, and the
  master a row above, so no link into it runs behind a bus.
- Links are sends: -60 to +12 dB, and a Mode on links out of a bus or a
  song. Out of a sound, an instrument or a pattern a link always takes
  the sound after its volume and FX. Loops are refused.
- A node without a link is silent and says "Goes nowhere".
- The rows Bus and Into are gone. Play nodes with a picked bus still
  overrule the routing.
- A click on a node shows its asset in the inspector, the Master shows
  the master volume and sound FX. A double click opens the asset's tab.
- The graph lives in project.routing and is held to the assets when a
  project is read, but nothing is added there. The editor adds the
  nodes when it opens a project. An asset without a node plays on the
  master, so old projects sound as before without a migration.
- In the mix an asset with one link at 0 dB goes straight into that bus.
  A sound or instrument with more gets a bus of its own with the sends.
  A pattern or song sends from the master of its playing, which is
  where its Mode taps. Buses of the mix can have sends now too.

Found:

- The check "the scheduler plans a looped bar" in e2e 34 wobbles. It
  failed in 2 of 5 runs here and in CI task 580 at 490fcba, before
  this change. HEAD passed it 2 of 2. Not fixed here.

Tests:

- Unit master-routing (new, 10), sound-library (2 new), buses
  rewritten onto the routing, 5 lists without the Bus row. 5 counter
  checks red.
- e2e 34 (melektaus-atx): ALL PASSED, 93 checks (3 new, 2 rewritten).
  Counter check with the Sound tab ignoring the routing: the routing
  check red.
- Gate (melektaus-atx): CHECK EXIT 0, 273 files, 4225 tests.

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

src/core/commands/routingCommands.ts

@@ -0,0 +1,32 @@
+import type { Project } from '../model/Project';
+import { type RoutingChange, redoRouting, settleRouting, undoRouting } from '../music/projectRouting';
+import type { Command } from './Command';
+
+/**
+ * Any edit, with the master routing held to the assets after it (#351): a node for an asset that
+ * came, none for one that went. Taken back and done again along with the edit, so an undone delete
+ * brings the links of its asset back too.
+ */
+export class KeepRoutingCommand implements Command {
+  private change: RoutingChange | null = null;
+  private settled = false;
+
+  constructor(readonly inner: Command) {}
+
+  get label(): string {
+    return this.inner.label;
+  }
+
+  execute(project: Project): void {
+    this.inner.execute(project);
+    if (!this.settled) {
+      this.change = settleRouting(project);
+      this.settled = true;
+    } else if (this.change) redoRouting(project, this.change);
+  }
+
+  undo(project: Project): void {
+    if (this.change) undoRouting(project, this.change);
+    this.inner.undo(project);
+  }
+}

src/core/commands/songCommands.ts

@@ -6,13 +6,14 @@
  */
 import type { EdgeSend, Graph } from '../graph/Graph';
 import type { Asset, SongAsset } from '../model/Asset';
-import type { Project } from '../model/Project';
+import { findGraphAsset, type Project } from '../model/Project';
 import { settleEmbedded } from '../music/embedded';
+import { routedKind, sendsTapped } from '../music/projectRouting';
 import { heldSend, heldSongGraph } from '../music/routing';
 import { heldSongItems, heldSongTracks, type SongItem, type SongTrack } from '../music/song';
 import { heldLoop, type LoopRange } from '../music/sequence';
 import { type Removed, removeWhere, restoreAt } from '../util/list';
-import type { Command } from './Command';
+import { type Command, CommandError } from './Command';
 import { requireEdge, requireSong } from './require';
 
 export interface SongParts {
@@ -75,7 +76,10 @@ export class SetSongCommand implements Command {
   }
 }
 
-/** How loud a link of a song's routing sends, and where it taps its track (#350). */
+/**
+ * How loud a link of a song's routing sends, and where it taps its track (#350); the same for a link
+ * of the master routing (#351), where only a bus and a song may tap anywhere but after their level.
+ */
 export class SetSendCommand implements Command {
   readonly label = 'Set send';
   private previous: EdgeSend | undefined;
@@ -87,10 +91,14 @@ export class SetSendCommand implements Command {
   ) {}
 
   execute(project: Project): void {
-    requireSong(project, this.assetId);
+    const holder = findGraphAsset(project, this.assetId);
+    if (holder?.type !== 'song' && holder?.type !== 'routing')
+      throw new CommandError(`Routing ${this.assetId} not found`);
     const edge = requireEdge(project, this.assetId, this.edgeId);
+    const from = holder.graph.nodes.find((n) => n.id === edge.from.node);
+    const tapped = holder.type === 'song' || (from !== undefined && sendsTapped(routedKind(from)));
     this.previous = edge.send;
-    const held = heldSend(this.send);
+    const held = heldSend(tapped ? this.send : { ...this.send, tap: 'post' });
     if (held) edge.send = held;
     else delete edge.send;
   }

src/core/model/Project.ts

@@ -6,6 +6,7 @@ import {
   isSceneAsset,
   type SceneAsset,
 } from './Asset';
+import { createEmptyGraph, type Graph } from '../graph/Graph';
 import { DEFAULT_LAYER_NAME } from './collisionLayers';
 import { DEFAULT_MASTER_VOLUME } from './master';
 import {
@@ -60,6 +61,11 @@ export interface Project {
    */
   masterVolume: number;
   masterFx: string;
+  /**
+   * Where the sounds, instruments, patterns, songs and buses go (#351): the graph of the Master
+   * routing tab. A project written before there was one has every one of them on the master.
+   */
+  routing: Graph;
   /**
    * Size of the scene view's symbol icons as a factor, 0.1 to 4 (see `symbolScale.ts`). A project
    * written before there was one reads as 1, the size the icons always had.
@@ -90,6 +96,7 @@ export function createEmptyProject(id: string, name: string): Project {
     renderLayers: [DEFAULT_LAYER_NAME],
     masterVolume: DEFAULT_MASTER_VOLUME,
     masterFx: '',
+    routing: createEmptyGraph(),
     symbolScale: DEFAULT_SYMBOL_SCALE,
     playFrom: DEFAULT_PLAY_FROM,
     whilePlaying: DEFAULT_WHILE_PLAYING,
@@ -122,7 +129,23 @@ export function findScene(project: Project, sceneId: string): SceneAsset | undef
   return asset && isSceneAsset(asset) ? asset : undefined;
 }
 
-export function findGraphAsset(project: Project, assetId: string): GraphAsset | undefined {
+/** The id the master routing (#351) goes by where a graph is looked up; no asset id has a `#`. */
+export const ROUTING_ID = '#routing';
+
+/** The master routing (#351) where a graph editor and its commands look for an asset's graph. */
+export interface RoutingHolder {
+  id: typeof ROUTING_ID;
+  type: 'routing';
+  name: string;
+  graph: Graph;
+}
+
+export type GraphHolder = GraphAsset | RoutingHolder;
+
+/** The graph asset by its id – or the master routing by `ROUTING_ID`, which is no asset. */
+export function findGraphAsset(project: Project, assetId: string): GraphHolder | undefined {
+  if (assetId === ROUTING_ID)
+    return { id: ROUTING_ID, type: 'routing', name: 'Master routing', graph: project.routing };
   const asset = findAsset(project, assetId);
   return asset && isGraphAsset(asset) ? asset : undefined;
 }

src/core/music/embedded.ts

@@ -22,12 +22,11 @@ import { signOf } from './time';
 export const EMBEDDABLE_TYPES: readonly AssetType[] = ['sound', 'pattern', 'soundfx'];
 
 /**
- * The rows of an embedded asset that do nothing in a song: where it goes and how it repeats is the
- * song's. A pattern keeps its tempo and meter (#363), as one of the project does.
+ * The rows of an embedded asset that do nothing in a song: how it repeats is the song's. A pattern
+ * keeps its tempo and meter (#363), as one of the project does.
  */
 const HIDDEN_ROWS: Partial<Record<AssetType, readonly string[]>> = {
-  sound: ['loop', 'bus'],
-  pattern: ['bus'],
+  sound: ['loop'],
 };
 
 export function isEmbeddable(type: AssetType): boolean {

src/core/music/mixer.ts

@@ -1,20 +1,38 @@
+import type { SendTap } from '../graph/Graph';
 import { findAssetOf, type Project } from '../model/Project';
-import type { PropertyBag } from '../model/Properties';
-import { BUS_FX_KEY, busInto, busOf, busVolumeOf, MASTER_BUS } from '../properties/buses';
+import { BUS_FX_KEY, busVolumeOf, MASTER_BUS } from '../properties/buses';
 import { coerceAs } from '../properties/kinds';
 import type { FxVoice } from '../soundfx/nodes';
 import { fxVoiceOf } from './needs';
+import { isRouted } from './projectRouting';
+import { sendOf } from './routing';
+import { dbToGain } from './song';
 import { DEFAULT_TEMPO } from './time';
 
 /** What the sound library calls the master bus (#325); every other bus of the mix is `mix:<id>`. */
 export const MASTER_MIX = 'mix';
 
+/** One link of the master routing (#351) as the mix plays it: into that bus, at that level, from that tap. */
+export interface MixSend {
+  to: string;
+  gain: number;
+  tap: SendTap;
+}
+
+/**
+ * Where something of the project goes (#351): straight into one bus of the mix, as one link at 0 dB
+ * does, or along its links. No link at all is no send, and silent.
+ */
+export type MixRoute = string | readonly MixSend[];
+
 /** One bus of the mix as the sound library sets it up: its level, its sound FX and where it goes. */
 export interface MixBus {
   name: string;
   volume: number;
   /** The bus it goes into; null for the master, which is heard. */
   into: string | null;
+  /** Where it goes instead, along the links of the routing (#351); `into` then says nothing. */
+  sends?: readonly MixSend[];
   fx: FxVoice | null;
 }
 
@@ -24,29 +42,61 @@ export function mixBusName(busId: string): string {
 }
 
 /**
- * The master and every bus of the project (#325), each into the bus it names – or the master, where
- * that is missing or would make a loop. A sound FX that does not compile is none.
+ * Where an asset goes by the master routing (#351). One the routing has no node for goes into the
+ * master, as every asset of a project written before there was a routing did. A link to what is
+ * neither a bus nor the master counts for nothing.
+ */
+export function routeOf(project: Project, assetId: string): MixRoute {
+  const graph = project.routing;
+  if (!graph.nodes.some((node) => node.id === assetId)) return MASTER_MIX;
+  const sends = graph.edges.flatMap((edge) => {
+    const to = edge.to.node;
+    if (edge.from.node !== assetId || (to !== MASTER_BUS && !findAssetOf(project, to, 'bus'))) return [];
+    const { volume, tap } = sendOf(edge);
+    return [{ to: mixBusName(to), gain: dbToGain(volume), tap }];
+  });
+  const only = sends.length === 1 ? sends[0]! : null;
+  return only && only.gain === 1 && only.tap === 'post' ? only.to : sends;
+}
+
+/**
+ * The master and every bus of the project (#325), each where the routing sends it (#351); and a bus
+ * of its own for each sound and instrument the routing sends anywhere but straight into one bus, for
+ * all its voices to go through. A sound FX that does not compile is none.
  */
 export function mixOf(project: Project): MixBus[] {
   const fxOf = (id: string) => fxVoiceOf(project, id, DEFAULT_TEMPO);
-  const buses = project.assets.flatMap((asset) =>
-    asset.type === 'bus'
-      ? [
-          {
-            name: mixBusName(asset.id),
-            volume: busVolumeOf(asset.props),
-            into: mixBusName(busInto(project, asset.id)),
-            fx: fxOf(coerceAs(asset.props[BUS_FX_KEY], 'asset', '')),
-          },
-        ]
-      : [],
-  );
+  const routed = (route: MixRoute) =>
+    typeof route === 'string' ? { into: route } : { into: MASTER_MIX, sends: route };
+  const buses = project.assets.flatMap((asset): MixBus[] => {
+    if (asset.type === 'bus')
+      return [
+        {
+          name: mixBusName(asset.id),
+          volume: busVolumeOf(asset.props),
+          ...routed(routeOf(project, asset.id)),
+          fx: fxOf(coerceAs(asset.props[BUS_FX_KEY], 'asset', '')),
+        },
+      ];
+    if ((asset.type !== 'sound' && asset.type !== 'instrument') || !isRouted(asset)) return [];
+    const route = routeOf(project, asset.id);
+    return typeof route === 'string'
+      ? []
+      : [{ name: mixBusName(asset.id), volume: 1, into: MASTER_MIX, sends: route, fx: null }];
+  });
   return [
     { name: MASTER_MIX, volume: project.masterVolume, into: null, fx: fxOf(project.masterFx) },
     ...buses,
   ];
 }
 
+const sameSends = (a: readonly MixSend[] | undefined, b: readonly MixSend[] | undefined) =>
+  a === b ||
+  (a !== undefined &&
+    b !== undefined &&
+    a.length === b.length &&
+    a.every((send, i) => send.to === b[i]!.to && send.gain === b[i]!.gain && send.tap === b[i]!.tap));
+
 /** Whether two mixes set the buses up the same: the same plan of a sound FX is the same object. */
 export function sameMix(a: readonly MixBus[], b: readonly MixBus[]): boolean {
   return (
@@ -57,6 +107,7 @@ export function sameMix(a: readonly MixBus[], b: readonly MixBus[]): boolean {
         bus.name === other.name &&
         bus.volume === other.volume &&
         bus.into === other.into &&
+        sameSends(bus.sends, other.sends) &&
         bus.fx?.plan === other.fx?.plan &&
         bus.fx?.tempo === other.fx?.tempo
       );
@@ -65,13 +116,20 @@ export function sameMix(a: readonly MixBus[], b: readonly MixBus[]): boolean {
 }
 
 /**
- * The bus of the mix something is heard on: the one a node picked, else the one its asset names.
+ * The bus of the mix a voice of a sound or an instrument is heard on: the one a node picked, else
+ * where the routing sends the asset (#351) – its own bus, where that is more than one bus.
  * A pick naming no bus any more is the master, as a deleted bus would leave it.
  */
-export function playedBus(project: Project, picked: string, assetProps: PropertyBag): string {
-  const id = picked !== '' ? picked : busOf(assetProps);
-  if (id === MASTER_BUS || id === '') return MASTER_MIX;
-  return findAssetOf(project, id, 'bus') ? mixBusName(id) : MASTER_MIX;
+export function playedBus(project: Project, picked: string, assetId: string): string {
+  const route = playedRoute(project, picked, assetId);
+  return typeof route === 'string' ? route : mixBusName(assetId);
+}
+
+/** Where a playing of a pattern or a song goes: the bus a node picked, else along its routing (#351). */
+export function playedRoute(project: Project, picked: string, assetId: string): MixRoute {
+  if (picked === MASTER_BUS) return MASTER_MIX;
+  if (picked !== '') return findAssetOf(project, picked, 'bus') ? mixBusName(picked) : MASTER_MIX;
+  return routeOf(project, assetId);
 }
 
 /** The bus of the mix a node reaches where an empty pick is the master: Set bus volume, Bus volume. */

src/core/music/playbacks.ts

@@ -1,5 +1,6 @@
 import type { SendTap } from '../graph/Graph';
 import type { FxPlan, FxVoice } from '../soundfx/nodes';
+import type { MixSend } from './mixer';
 import { LEAD, type ScheduledClip, type ScheduledNote, Scheduler, type SchedulerHost } from './Scheduler';
 import type { LoopRange, Sequence } from './sequence';
 
@@ -47,6 +48,8 @@ export interface SequencePlay {
   fx?: FxVoice;
   /** The bus of the mix the whole playing is heard on (#325); the master where left out. */
   bus?: string;
+  /** Where the whole playing goes instead, along the links of the master routing (#351). */
+  sends?: readonly MixSend[];
   /** Starts one note as the player was asked to, and gives back the number of its voice. */
   strike(note: ScheduledNote): number;
   strikeClip?(clip: ScheduledClip): number;

src/core/music/projectRouting.ts

@@ -0,0 +1,240 @@
+/**
+ * The master routing of a project (#351): a graph with a node per sound, instrument, pattern, song and
+ * bus, and the master, its links the sends from one to the next. Its nodes follow the assets: one
+ * that comes gets a node of its own and a link to the master, one that goes takes its node along.
+ */
+import { createEmptyGraph, type Graph, type GraphEdge, type GraphNode, reaches } from '../graph/Graph';
+import { newId } from '../ids';
+import type { Asset } from '../model/Asset';
+import type { AssetType } from '../model/AssetTypes';
+import { textOf } from '../model/Properties';
+import type { Project } from '../model/Project';
+import { MASTER_BUS } from '../properties/buses';
+import { type Removed, removeWhere, restoreAt } from '../util/list';
+import { isEmbedded } from './embedded';
+import { heldSend } from './routing';
+import { ROUTED_ASSET, ROUTED_KIND, ROUTED_MASTER, ROUTED_NAME } from './routingNodes';
+
+export const ROUTED_TYPES: readonly AssetType[] = ['sound', 'instrument', 'pattern', 'song', 'bus'];
+/** What has its own sound FX and level on a bus of its own, and so may send from before them. */
+const TAPPED_TYPES: readonly AssetType[] = ['bus', 'song'];
+
+/**
+ * Where a new node goes: what plays in the first column, by type, the buses in the second, the
+ * master in the third a row above the rest, so no link into it runs behind a bus.
+ */
+const COLUMN_STEP = 320;
+const ROW_STEP = 80;
+const COLUMN_OF = (type: string) => (type === 'bus' ? 1 : 0);
+const MASTER_COLUMN = 2;
+
+export function isRouted(asset: Asset): boolean {
+  return ROUTED_TYPES.includes(asset.type) && !isEmbedded(asset);
+}
+
+/** Whether links out of an asset of this type may take the sound before its sound FX or its level. */
+export function sendsTapped(type: string): boolean {
+  return (TAPPED_TYPES as readonly string[]).includes(type);
+}
+
+/** The asset type a node of the routing stands for, `''` for the master. */
+export function routedKind(node: GraphNode): string {
+  return node.type === ROUTED_ASSET ? textOf(node.params[ROUTED_KIND] ?? '') : '';
+}
+
+/**
+ * The routing as it has to be for the assets of the project: a node for each, named after it, and
+ * the master. An asset without a node gets one below the others of its column and a link to the master
+ * – every asset of a project written before there was a routing. A link goes where one of its ends
+ * is gone, where it would close a loop or say again what another one says; a node whose every link
+ * led to a bus that is gone is linked to the master instead, so deleting a bus silences nothing.
+ * Without `adding`, as a project is read, an asset without a node stays without one – it is heard on
+ * the master all the same (`routeOf`) – and the master is added only to a routing that has nodes.
+ */
+export function heldRouting(graph: Graph | undefined, assets: readonly Asset[], adding = true): Graph {
+  const given = graph ?? createEmptyGraph();
+  const routed = new Map(assets.filter(isRouted).map((asset) => [asset.id, asset]));
+  const paramsOf = (asset: Asset) => ({ [ROUTED_NAME]: asset.name, [ROUTED_KIND]: asset.type });
+  // What stands keeps its place in the list, so a project reads back as it was written.
+  const nodes: GraphNode[] = given.nodes.flatMap((node) => {
+    if (node.id === MASTER_BUS) return node.type === ROUTED_MASTER ? [node] : [];
+    const asset = routed.get(node.id);
+    return asset && routedKind(node) === asset.type
+      ? [{ ...node, params: { ...node.params, ...paramsOf(asset) } }]
+      : [];
+  });
+  const placed = new Set(nodes.map((node) => node.id));
+  const lowest = new Map<number, number>();
+  for (const node of nodes) {
+    const column = COLUMN_OF(routedKind(node));
+    if (node.type === ROUTED_ASSET) lowest.set(column, Math.max(lowest.get(column) ?? -Infinity, node.y));
+  }
+  const fresh = new Set<string>();
+  const order = (asset: Asset) => ROUTED_TYPES.indexOf(asset.type);
+  if (adding)
+    for (const asset of [...routed.values()].sort((a, b) => order(a) - order(b))) {
+      if (placed.has(asset.id)) continue;
+      fresh.add(asset.id);
+      const column = COLUMN_OF(asset.type);
+      const y = (lowest.get(column) ?? -ROW_STEP) + ROW_STEP;
+      lowest.set(column, y);
+      nodes.push({ id: asset.id, type: ROUTED_ASSET, x: column * COLUMN_STEP, y, params: paramsOf(asset) });
+    }
+  if (!placed.has(MASTER_BUS) && (adding || nodes.length > 0)) {
+    const top = Math.min(0, ...nodes.map((node) => node.y));
+    nodes.push({
+      id: MASTER_BUS,
+      type: ROUTED_MASTER,
+      x: MASTER_COLUMN * COLUMN_STEP,
+      y: top - ROW_STEP,
+      params: {},
+    });
+  }
+
+  const kinds = new Map(nodes.map((node) => [node.id, routedKind(node)]));
+  const takesIn = (id: string) => id === MASTER_BUS || kinds.get(id) === 'bus';
+  const edges: GraphEdge[] = [];
+  const edgeIds = new Set<string>();
+  const lost = new Set<string>();
+  for (const edge of given.edges) {
+    const from = edge.from.node;
+    const to = edge.to.node;
+    const kind = kinds.get(from);
+    if (!kind || fresh.has(from) || edge.from.port !== 'out') continue;
+    if (!takesIn(to) || edge.to.port !== 'in') {
+      lost.add(from);
+      continue;
+    }
+    if (from === to || edgeIds.has(edge.id)) continue;
+    if (edges.some((e) => e.from.node === from && e.to.node === to)) continue;
+    if (to !== MASTER_BUS && reaches({ edges }, to, from)) continue;
+    edgeIds.add(edge.id);
+    const raw = heldSend(edge.send);
+    const send = raw && !sendsTapped(kind) ? heldSend({ ...raw, tap: 'post' }) : raw;
+    edges.push({
+      id: edge.id,
+      from: { node: from, port: 'out' },
+      to: { node: to, port: 'in' },
+      ...(edge.folded && { folded: true }),
+      ...(send && { send }),
+    });
+  }
+  const linked = new Set(edges.map((e) => e.from.node));
+  for (const node of nodes)
+    if (fresh.has(node.id) || (lost.has(node.id) && !linked.has(node.id)))
+      edges.push({ id: newId(), from: { node: node.id, port: 'out' }, to: { node: MASTER_BUS, port: 'in' } });
+  return {
+    nodes,
+    edges,
+    ...(given.groups && { groups: given.groups }),
+    ...(given.notes && { notes: given.notes }),
+  };
+}
+
+/** What one settling of the routing changed, by id, so it can be taken back and done again. */
+export interface RoutingChange {
+  nodes: { added: GraphNode[]; removed: Removed<GraphNode>[]; renamed: RenamedNode[] };
+  edges: { added: GraphEdge[]; removed: Removed<GraphEdge>[] };
+}
+
+interface RenamedNode {
+  id: string;
+  before: GraphNode['params'];
+  after: GraphNode['params'];
+}
+
+/**
+ * Holds the routing of the project to its assets (`heldRouting`), in place: nodes and links stay
+ * the objects they are, so what an undo of another edit holds on to still finds them. Null where
+ * nothing had to change.
+ */
+export function settleRouting(project: Project): RoutingChange | null {
+  const graph = project.routing;
+  const held = heldRouting(graph, project.assets);
+  const heldNodes = new Map(held.nodes.map((n) => [n.id, n]));
+  const heldEdges = new Map(held.edges.map((e) => [e.id, e]));
+  const bare = ({ params: _, ...node }: GraphNode) => JSON.stringify(node);
+  // A node that is another thing now goes and comes anew; one that only reads another name keeps itself.
+  const removedNodes = new Set(
+    graph.nodes
+      .filter((n) => !heldNodes.has(n.id) || bare(heldNodes.get(n.id)!) !== bare(n))
+      .map((n) => n.id),
+  );
+  const removedEdges = new Set(
+    graph.edges.filter((e) => JSON.stringify(heldEdges.get(e.id)) !== JSON.stringify(e)).map((e) => e.id),
+  );
+  const standing = new Set(graph.nodes.map((n) => n.id).filter((id) => !removedNodes.has(id)));
+  const kept = new Set(graph.edges.map((e) => e.id).filter((id) => !removedEdges.has(id)));
+  const renamed: RenamedNode[] = graph.nodes.flatMap((node) => {
+    const after = heldNodes.get(node.id)?.params;
+    return standing.has(node.id) && after && JSON.stringify(after) !== JSON.stringify(node.params)
+      ? [{ id: node.id, before: node.params, after }]
+      : [];
+  });
+  const change: RoutingChange = {
+    nodes: { added: held.nodes.filter((n) => !standing.has(n.id)), removed: [], renamed },
+    edges: { added: held.edges.filter((e) => !kept.has(e.id)), removed: [] },
+  };
+  if (
+    removedNodes.size +
+      removedEdges.size +
+      renamed.length +
+      change.nodes.added.length +
+      change.edges.added.length ===
+    0
+  )
+    return null;
+  applyRouting(project, change, removedNodes, removedEdges);
+  return change;
+}
+
+function applyRouting(
+  project: Project,
+  change: RoutingChange,
+  removedNodes: ReadonlySet<string>,
+  removedEdges: ReadonlySet<string>,
+): void {
+  const graph = project.routing;
+  change.edges.removed = removeWhere(graph.edges, (e) => removedEdges.has(e.id));
+  change.nodes.removed = removeWhere(graph.nodes, (n) => removedNodes.has(n.id));
+  for (const { id, after } of change.nodes.renamed) {
+    const node = graph.nodes.find((n) => n.id === id);
+    if (node) node.params = after;
+  }
+  graph.nodes.push(...change.nodes.added);
+  graph.edges.push(...change.edges.added);
+}
+
+/** Does a settling again, as it was done the first time. */
+export function redoRouting(project: Project, change: RoutingChange): void {
+  applyRouting(
+    project,
+    change,
+    new Set(change.nodes.removed.map((r) => r.item.id)),
+    new Set(change.edges.removed.map((r) => r.item.id)),
+  );
+}
+
+/** Takes a settling back: what it added goes, what it took comes back where it was. */
+export function undoRouting(project: Project, change: RoutingChange): void {
+  const graph = project.routing;
+  const addedNodes = new Set(change.nodes.added.map((n) => n.id));
+  const addedEdges = new Set(change.edges.added);
+  graph.edges.splice(0, graph.edges.length, ...graph.edges.filter((e) => !addedEdges.has(e)));
+  graph.nodes.splice(0, graph.nodes.length, ...graph.nodes.filter((n) => !addedNodes.has(n.id)));
+  for (const { id, before } of change.nodes.renamed) {
+    const node = graph.nodes.find((n) => n.id === id);
+    if (node) node.params = before;
+  }
+  restoreAt(graph.nodes, change.nodes.removed);
+  restoreAt(graph.edges, change.edges.removed);
+}
+
+/** What is wrong with a node of the routing, by node id: one that goes nowhere is never heard. */
+export function masterRoutingProblems(graph: Graph): Record<string, string> {
+  const problems: Record<string, string> = {};
+  for (const node of graph.nodes)
+    if (node.type === ROUTED_ASSET && !graph.edges.some((e) => e.from.node === node.id))
+      problems[node.id] = 'Goes nowhere: link it to a bus or to the master to hear it';
+  return problems;
+}

src/core/music/routingNodes.ts

@@ -39,3 +39,57 @@ export const SongOutputNode = registerNode({
 export function isSongRoutingDef(def: NodeDef): boolean {
   return def.type === SONG_TRACK || def.type === SONG_OUTPUT;
 }
+
+/**
+ * The nodes of the master routing (#351): one per sound, instrument, pattern, song and bus of the
+ * project, named and typed after its asset, and the master. Only a bus and the master take links in.
+ */
+export const ROUTED_ASSET = 'RoutedAsset';
+export const ROUTED_MASTER = 'RoutedMaster';
+export const ROUTED_NAME = 'name';
+export const ROUTED_KIND = 'kind';
+
+const KIND_WORDS: Record<string, string> = {
+  sound: 'Sound',
+  instrument: 'Instrument',
+  pattern: 'Pattern',
+  song: 'Song',
+  bus: 'Bus',
+};
+
+export const RoutedAssetNode = registerNode({
+  type: ROUTED_ASSET,
+  label: 'Asset',
+  category: 'sound',
+  description:
+    'A sound, an instrument, a pattern, a song or a bus of the project: all it plays, sent on to every link.',
+  inputs: [],
+  outputs: [],
+  params: [],
+  fixed: true,
+  acyclic: true,
+  derivePorts: ({ node }) => {
+    const kind = textOf(node.params[ROUTED_KIND] ?? '');
+    return {
+      label: textOf(node.params[ROUTED_NAME] ?? '') || 'Asset',
+      inputs: kind === 'bus' ? [audioIn] : [],
+      outputs: [{ ...audioOut, label: KIND_WORDS[kind] ?? 'out' }],
+    };
+  },
+});
+
+export const RoutedMasterNode = registerNode({
+  type: ROUTED_MASTER,
+  label: 'Master',
+  category: 'sound',
+  description: 'Where the game is heard: through the volume and the sound FX of the master to the speakers.',
+  inputs: [audioIn],
+  outputs: [],
+  params: [],
+  fixed: true,
+  acyclic: true,
+});
+
+export function isMasterRoutingDef(def: NodeDef): boolean {
+  return def.type === ROUTED_ASSET || def.type === ROUTED_MASTER;
+}

src/core/properties/PropertySchema.ts

@@ -124,7 +124,7 @@ import {
 } from '../music/song';
 import { DEFAULT_SIGN, DEFAULT_TEMPO, MAX_TEMPO, MIN_TEMPO, SIGN_OPTIONS } from '../music/time';
 import { ASSET_FX_KEY } from './assetFx';
-import { BUS_FX_KEY, BUS_INTO_KEY, BUS_KEY, BUS_VOLUME_KEY } from './buses';
+import { BUS_FX_KEY, BUS_VOLUME_KEY } from './buses';
 import { Theme } from '../../ui';
 
 /**
@@ -133,9 +133,7 @@ import { Theme } from '../../ui';
  * produces fractions, and the field rounds the value away rather than hiding it. Without
  * `assetTypes` an asset picker offers every placeable asset; `none` is what it calls an empty pick,
  * `master` offers the master bus as a choice of its own, `noFx` "None" as one where empty means
- * "from the asset" (#352), and `intoFor` names the bus the row is
- * the Into of, which leaves out that bus and every one going into it when the picker opens (#325);
- * `uploadedOnly` keeps drawn pictures out
+ * "from the asset" (#352); `uploadedOnly` keeps drawn pictures out
  * of a texture picker (#186). `renderLayers` makes a layer row pick from the project's render layers
  * instead of its collision layers (#302), with "Inherit" as the first choice of a single layer.
  */
@@ -149,7 +147,6 @@ type Extras<K extends FlatKind> = K extends 'number'
           none?: string;
           master?: boolean;
           noFx?: boolean;
-          intoFor?: string;
         }
       : K extends 'texture'
         ? { uploadedOnly?: boolean }
@@ -485,16 +482,6 @@ const SLICE_SCALE_ROW: PropertyDef = {
   step: 0.1,
 };
 
-/** The bus a sound, an instrument, a pattern or a song is heard on (#325). */
-const BUS_ROW: PropertyDef = {
-  key: BUS_KEY,
-  label: 'Bus',
-  kind: 'asset',
-  default: '',
-  assetTypes: ['bus'],
-  none: 'Master',
-};
-
 /** The sound FX a sound, an instrument, a pattern or a song goes through, before its bus (#352). */
 const FX_ROW: PropertyDef = {
   key: ASSET_FX_KEY,
@@ -706,12 +693,11 @@ const ASSET_SCHEMAS: Record<AssetType, PropertySchema> = {
     { key: SOUND_VOLUME_KEY, label: 'Volume', kind: 'number', default: 1, min: 0, max: 1, step: 0.05 },
     { key: SOUND_LOOP_KEY, label: 'Loop', kind: 'boolean', default: false },
     FX_ROW,
-    BUS_ROW,
   ],
   // The effects are the asset's graph (see SoundFxAsset), not a property.
   soundfx: [],
   // What a note sounds like is the asset's graph (see InstrumentAsset), not a property.
-  instrument: [FX_ROW, BUS_ROW],
+  instrument: [FX_ROW],
   // The notes and the loop are intrinsic data on the asset (see PatternAsset). The meter and the
   // tempo are for drawing and hearing it on its own; a song plays it at its own tempo (#334).
   pattern: [
@@ -744,7 +730,6 @@ const ASSET_SCHEMAS: Record<AssetType, PropertySchema> = {
       step: 1,
     },
     FX_ROW,
-    BUS_ROW,
   ],
   // The tracks, items and loop are intrinsic data on the asset (see SongAsset).
   song: [
@@ -766,13 +751,12 @@ const ASSET_SCHEMAS: Record<AssetType, PropertySchema> = {
       options: SONG_GRID_OPTIONS,
     },
     FX_ROW,
-    BUS_ROW,
   ],
-  // Where sounds are mixed (#325): how loud, through which sound FX, and on into which bus.
+  // Where sounds are mixed (#325): how loud and through which sound FX. Where it goes on is the
+  // master routing's (#351).
   bus: [
     { key: BUS_VOLUME_KEY, label: 'Volume', kind: 'number', default: 1, min: 0, max: 1, step: 0.05 },
     { key: BUS_FX_KEY, label: 'Sound FX', kind: 'asset', default: '', assetTypes: ['soundfx'] },
-    { ...BUS_ROW, key: BUS_INTO_KEY, label: 'Into' },
   ],
   // How many particles and for how long; what one of them does is the asset's graph, whose Property
   // nodes add their rows after these – see `schemaForBag`.
@@ -1121,11 +1105,6 @@ function schemaForBag(project: Project, asset: Asset, bag: PropertyBag): Propert
   // Nothing but declarations: the starting values live in `props` under the very same keys.
   if (asset.type === 'variables' || asset.type === 'struct') return asset.variables;
   if (asset.type === 'sprite') return [...FULL_SCHEMAS.sprite, ...shaderParamRows(project, shaderOf(bag))];
-  // A bus never goes into itself, nor into one that already goes into it.
-  if (asset.type === 'bus')
-    return FULL_SCHEMAS.bus.map((def) =>
-      def.key === BUS_INTO_KEY && def.kind === 'asset' ? { ...def, intoFor: asset.id } : def,
-    );
   // Unlike a sprite's shader, a source's graph is its own asset's, so no id has to be looked up.
   if (asset.type === 'particles')
     return sourceRows(

src/core/properties/buses.ts

@@ -1,59 +1,18 @@
-import { findAssetOf, type Project } from '../model/Project';
 import type { PropertyBag } from '../model/Properties';
 import { coerceAs } from './kinds';
 
-/** The bus a sound, an instrument, a pattern or a song is heard on (#325); empty is the master. */
-export const BUS_KEY = 'bus';
 /** How loud a bus is, 0–1. */
 export const BUS_VOLUME_KEY = 'volume';
 /** The sound FX all of a bus goes through, before its volume. */
 export const BUS_FX_KEY = 'fx';
-/** The bus a bus goes into; empty is the master. */
-export const BUS_INTO_KEY = 'into';
 
 /**
  * What a node picks to name the master where empty means something else: "from the asset" on a
- * Play node, "no bus" on Set sound FX parameters. No asset id has a `#`.
+ * Play node, "no bus" on Set sound FX parameters. No asset id has a `#`. It is also the id of the
+ * master in the master routing (#351).
  */
 export const MASTER_BUS = '#master';
 
-export function busOf(bag: PropertyBag): string {
-  return coerceAs(bag[BUS_KEY], 'asset', '');
-}
-
 export function busVolumeOf(bag: PropertyBag): number {
   return Math.max(0, Math.min(1, coerceAs(bag[BUS_VOLUME_KEY], 'number', 1)));
 }
-
-/** The bus a bus says it goes into, where that is a bus; '' for the master. */
-function namedInto(project: Project, busId: string): string {
-  const bus = findAssetOf(project, busId, 'bus');
-  const into = bus ? coerceAs(bus.props[BUS_INTO_KEY], 'asset', '') : '';
-  return into !== '' && findAssetOf(project, into, 'bus') ? into : '';
-}
-
-/** Whether following the buses on from `from` comes to `to`. */
-function reaches(project: Project, from: string, to: string): boolean {
-  const seen = new Set<string>();
-  for (let at = from; at !== '' && !seen.has(at); at = namedInto(project, at)) {
-    if (at === to) return true;
-    seen.add(at);
-  }
-  return false;
-}
-
-/**
- * The bus a bus goes into, '' for the master. One that would come round to itself goes into the
- * master instead, so however a project was written the buses never run in a loop.
- */
-export function busInto(project: Project, busId: string): string {
-  const into = namedInto(project, busId);
-  return into !== '' && reaches(project, into, busId) ? '' : into;
-}
-
-/** The buses a bus cannot go into: itself and every one that already goes into it. */
-export function busesInto(project: Project, busId: string): string[] {
-  return project.assets
-    .filter((asset) => asset.type === 'bus' && reaches(project, asset.id, busId))
-    .map((asset) => asset.id);
-}

src/core/store/serialize.ts

@@ -25,7 +25,8 @@ import { heldPatternNotes } from '../music/pattern';
 import { isEmbeddable } from '../music/embedded';
 import { heldSongItems, heldSongTracks } from '../music/song';
 import { heldSend, heldSongGraph } from '../music/routing';
-import { isSongRoutingDef } from '../music/routingNodes';
+import { isMasterRoutingDef, isSongRoutingDef } from '../music/routingNodes';
+import { heldRouting } from '../music/projectRouting';
 import { heldLoop, type LoopRange } from '../music/sequence';
 import { isKeyInterpolation, normalizeKeys } from '../model/animation';
 import type {
@@ -340,6 +341,7 @@ export function deserializeProject(raw: unknown, fallbackId = ''): Project {
     renderLayers: renderLayersOf(r),
     masterVolume: masterVolumeOf(r),
     masterFx: masterFxOf(r),
+    routing: heldRouting(normalizeGraph(r.routing, isMasterRoutingDef), assets, false),
     symbolScale: symbolScaleOf(r),
     playFrom: playFromOf(r),
     whilePlaying: whilePlayingOf(r),

src/editor/Editor.ts

@@ -1,6 +1,6 @@
 import type { Application, Ticker } from 'pixi.js';
 import type { Asset } from '../core/model/Asset';
-import { findAsset, findObjectHolder } from '../core/model/Project';
+import { findAsset, findObjectHolder, ROUTING_ID } from '../core/model/Project';
 import { assetTitle } from '../core/music/embedded';
 import { mixOf } from '../core/music/mixer';
 import type { Role } from '../core/store/AuthStore';
@@ -94,6 +94,7 @@ import type { PluginManager } from './plugins/loader';
 import { PluginsPane } from './plugins/PluginsPane';
 import { ManagementPane } from './users/ManagementPane';
 import { UsersPane } from './users/UsersPane';
+import { RoutingEditor } from './routing/RoutingEditor';
 
 export type CentreTab =
   | 'scene'
@@ -115,6 +116,7 @@ export type CentreTab =
   | 'tile'
   | 'container'
   | 'variables'
+  | 'routing'
   | 'management';
 
 /** A tab a plugin added; the prefix keeps it apart from every built-in one. */
@@ -123,10 +125,10 @@ export type PluginTabId = `plugin:${string}`;
 export type TabId = CentreTab | PluginTabId;
 /**
  * An open document (#171): an asset by its id, or what a Variables tab shows (#252) by its
- * `valuesKey` – as many of those as were opened. The user management (#179) is no document, but it
- * opens and closes like one.
+ * `valuesKey` – as many of those as were opened. The user management (#179) and the master routing
+ * (#351) are no documents, but they open and close like one.
  */
-export type DocumentId = `asset:${string}` | `values:${string}` | 'management';
+export type DocumentId = `asset:${string}` | `values:${string}` | 'routing' | 'management';
 /** The account behind this session; the menu for it sits at the far right of the toolbar. */
 export interface EditorAccount {
   /** Who is signed in – the menu says so, since the toolbar has no room for a second label. */
@@ -144,7 +146,7 @@ export type StripTab = FixedTab | PluginTabId | DocumentId;
 
 type FixedTab = (typeof FIXED_TABS)[number];
 /** The kinds whose documents are assets, each shown by one editor that is pointed at them in turn. */
-type AssetKind = Exclude<CentreTab, FixedTab | 'variables' | 'management'>;
+type AssetKind = Exclude<CentreTab, FixedTab | 'variables' | 'routing' | 'management'>;
 
 const FIXED_TABS = ['scene', 'game'] as const;
 
@@ -168,6 +170,7 @@ const PANE_ORDER = [
   'tile',
   'container',
   'variables',
+  'routing',
   'management',
 ] as const;
 
@@ -192,6 +195,7 @@ const TAB_LABELS: Record<CentreTab, string> = {
   tile: 'Tile',
   container: 'Container',
   variables: 'Variables',
+  routing: 'Master routing',
   management: 'User management',
 };
 
@@ -202,7 +206,7 @@ const FIXED_TAB_ICONS: Partial<Record<FixedTab, string>> = {
 };
 
 function isDocument(tab: StripTab): tab is DocumentId {
-  return tab === 'management' || tab.startsWith('asset:') || tab.startsWith('values:');
+  return tab === 'management' || tab === 'routing' || tab.startsWith('asset:') || tab.startsWith('values:');
 }
 
 const MIN_LEFT_WIDTH = 160;
@@ -245,6 +249,7 @@ export class Editor implements PlayHost {
   readonly tileEditor: TileEditor;
   readonly containerEditor: ContainerEditor;
   readonly variablesEditor: VariablesEditor;
+  readonly routingEditor: RoutingEditor;
   /** What each open Variables tab shows, by its document. */
   private readonly valueTargets = new Map<DocumentId, ValuesTarget>();
   /** The switch per file in `data/plugins/`, in the user management tab (#179). */
@@ -335,6 +340,7 @@ export class Editor implements PlayHost {
     this.tileEditor = new TileEditor(state);
     this.containerEditor = new ContainerEditor(state);
     this.variablesEditor = new VariablesEditor(state);
+    this.routingEditor = new RoutingEditor(state);
     this.hierarchy = new HierarchyPanel(state);
     this.inspector = new Inspector(state);
     this.tilemapPanel = new TilemapPanel(state);
@@ -383,7 +389,10 @@ export class Editor implements PlayHost {
     this.managementPane = new ManagementPane(this.usersPane, this.pluginsPane);
 
     this.toolbar = new Toolbar(state, {
-      openMainMenu: (anchor) => this.projects.openMainMenu(anchor, this.managementEntries()),
+      openMainMenu: (anchor) =>
+        this.projects.openMainMenu(anchor, this.managementEntries(), [
+          { label: 'Master routing', onSelect: () => this.openDocument('routing') },
+        ]),
       togglePlay: () => (state.mode === 'edit' ? this.play.play() : this.play.stop()),
       togglePause: () => this.play.togglePause(),
       openAccountMenu: (anchor) => this.openAccountMenu(anchor, account),
@@ -453,6 +462,7 @@ export class Editor implements PlayHost {
       game: this.gamePane,
       ...this.assetEditors,
       variables: this.variablesEditor,
+      routing: this.routingEditor,
       management: this.managementPane,
     };
     // Following a call goes on in the same tab: the tab changes its document, not its place.
@@ -532,7 +542,8 @@ export class Editor implements PlayHost {
     // creating it) is for – see the `open` event below.
     state.on('selection', () => {
       const s = state.selection;
-      if (s?.kind === 'node' || s?.kind === 'frame' || s?.kind === 'clip' || s?.kind === 'song')
+      if (s?.kind === 'node' && s.assetId === ROUTING_ID) this.openDocument('routing');
+      else if (s?.kind === 'node' || s?.kind === 'frame' || s?.kind === 'clip' || s?.kind === 'song')
         this.openDocument(`asset:${s.assetId}`);
       if (s?.kind === 'object' && findAsset(state.project, s.holderId)?.type === 'container')
         this.openDocument(`asset:${s.holderId}`);
@@ -791,6 +802,7 @@ export class Editor implements PlayHost {
     if (kind && kind in this.assetEditors)
       this.assetEditors[kind as AssetKind].forgetView(doc.slice('asset:'.length));
     this.valueTargets.delete(doc);
+    if (doc === 'routing') this.routingEditor.close();
     if (!wasShowing) return;
     if (this.documents.active) this.showDocument(this.documents.active);
     else this.showTab('scene');
@@ -807,8 +819,8 @@ export class Editor implements PlayHost {
       if (doc) this.openDocument(doc);
       return;
     }
-    if (tab === 'management') {
-      this.openDocument('management');
+    if (tab === 'management' || tab === 'routing') {
+      this.openDocument(tab);
       return;
     }
     if (tab in this.assetEditors) {
@@ -856,7 +868,7 @@ export class Editor implements PlayHost {
       const target = this.valueTargets.get(doc);
       return target && valuesTitle(this.state, target) !== null ? 'variables' : null;
     }
-    if (doc === 'management') return 'management';
+    if (doc === 'management' || doc === 'routing') return doc;
     const type = findAsset(this.state.project, doc.slice('asset:'.length))?.type;
     const kind = type ? TAB_OF_ASSET[type] : undefined;
     return kind && kind !== 'scene' ? kind : null;
@@ -870,12 +882,14 @@ export class Editor implements PlayHost {
     if (kind === 'variables' && target) this.variablesEditor.show(target);
     // Read on every showing: an account may have been changed from another tab in the meantime.
     if (kind === 'management') void this.usersPane?.reload();
+    if (kind === 'routing') this.routingEditor.open();
     this.display(kind, doc);
   }
 
   /** What a document's tab says: the asset's name, or what a Variables tab shows, as its header says. */
   private labelOf(doc: DocumentId): string {
     if (doc === 'management') return this.usersPane ? TAB_LABELS.management : 'Plugins';
+    if (doc === 'routing') return TAB_LABELS.routing;
     const target = this.valueTargets.get(doc);
     if (target) return valuesTitle(this.state, target, this.inspector.liveVariables) ?? '';
     const asset = findAsset(this.state.project, doc.slice('asset:'.length));
@@ -885,6 +899,7 @@ export class Editor implements PlayHost {
   /** The icon in front of a document's name: its asset type's, as in the asset panel. */
   private iconOf(doc: DocumentId): string {
     if (doc === 'management') return this.usersPane ? USERS_ICON_SVG : PLUGINS_ICON_SVG;
+    if (doc === 'routing') return ASSET_ICON_SVG.bus;
     const target = this.valueTargets.get(doc);
     if (target) return target.kind === 'list' ? LIST_ICON_SVG : ASSET_ICON_SVG.variables;
     const type = findAsset(this.state.project, doc.slice('asset:'.length))?.type;
@@ -900,7 +915,7 @@ export class Editor implements PlayHost {
       const kind = this.kindOf(doc);
       if (!this.tabs.has(doc) && kind)
         this.tabs.addTab(doc, this.labelOf(doc), base + index, {
-          kind: doc === 'management' ? this.labelOf(doc) : TAB_LABELS[kind],
+          kind: doc === 'management' || doc === 'routing' ? this.labelOf(doc) : TAB_LABELS[kind],
           icon: this.iconOf(doc),
           onClose: () => this.closeDocument(doc),
         });

src/editor/ProjectSession.ts

@@ -105,9 +105,10 @@ export class ProjectSession {
 
   /**
    * The one menu of the top bar (#183): everything that is about the project rather than a scene.
-   * `more` comes last – what the editor adds that is not about the project (#179).
+   * `project` is what the editor adds about it, after its settings (#351); `more` comes last – what
+   * the editor adds that is not about the project (#179).
    */
-  openMainMenu(anchor: Widget, more: MenuEntry[] = []): void {
+  openMainMenu(anchor: Widget, more: MenuEntry[] = [], project: MenuEntry[] = []): void {
     const items: MenuEntry[] = [
       { label: 'New project', onSelect: () => void this.run(this.createNext()) },
       { label: 'Open project…', onSelect: () => this.openProjectPicker() },
@@ -115,6 +116,7 @@ export class ProjectSession {
       { label: 'Snapshots…', onSelect: () => this.openSnapshots() },
       { label: 'Release…', onSelect: () => this.openRelease() },
       { label: 'Project settings…', onSelect: () => this.openProjectSettings() },
+      ...project,
       { label: 'Clear saved data', onSelect: () => this.clearSavedData() },
       ...more,
     ];

src/editor/clipboard.ts

@@ -13,12 +13,17 @@ import {
   namesBehavior,
   SHADER_CALL,
 } from '../core/graph';
-import type { GraphAsset } from '../core/model/Asset';
 import { type Clip, copyGraph, copyObjects, type GraphClip, type ObjectClip } from '../core/model/clipboard';
 import { findObject } from '../core/model/hierarchy';
 import { isLiveInstance } from '../core/model/instance';
 import type { Vec2 } from '../core/model/Properties';
-import { findGraphAsset, findObjectHolder, type ObjectHolder, type Project } from '../core/model/Project';
+import {
+  findGraphAsset,
+  findObjectHolder,
+  type GraphHolder,
+  type ObjectHolder,
+  type Project,
+} from '../core/model/Project';
 import { GRID_STEP } from './graph/graphView';
 import { paletteEntries } from './graph/paletteEntries';
 import { type EditorState, graphSelection, objectSelection } from './state';
@@ -158,7 +163,7 @@ export function pasteObjects(
 }
 
 /** Whether `asset`'s graph may hold `node`: the palette would offer its kind there. */
-function fitsGraph(project: Project, asset: GraphAsset, node: GraphNode): boolean {
+function fitsGraph(project: Project, asset: GraphHolder, node: GraphNode): boolean {
   return paletteEntries(project, asset).some(
     (entry) =>
       entry.def.type === node.type &&
@@ -170,7 +175,7 @@ function fitsGraph(project: Project, asset: GraphAsset, node: GraphNode): boolea
 /** The part of a graph copy `asset` can take, and the nodes it cannot. */
 function fittingPart(
   project: Project,
-  asset: GraphAsset,
+  asset: GraphHolder,
   clip: GraphClip,
 ): { clip: GraphClip; skipped: GraphNode[] } {
   const nodes = clip.nodes.filter((n) => fitsGraph(project, asset, n));

src/editor/debug/routingHooks.ts

@@ -0,0 +1,24 @@
+import { soundLibrary } from '../../viewport/SoundLibrary';
+import { centreOf, type HookContext } from './hookHelpers';
+
+/** The Master routing tab (#351): its graph, where its nodes, ports and links are, and the buses it makes. */
+export function routingHooks({ state, editor }: HookContext) {
+  const { routingEditor } = editor;
+  const canvas = routingEditor.canvas;
+  return {
+    routing: {
+      shown: () => editor.tab === 'routing' && canvas.currentAssetId !== '',
+      info: () => routingEditor.shownInfo,
+      graph: () => JSON.parse(JSON.stringify(state.project.routing)) as unknown,
+      portAt: (nodeId: string, port: string, isOutput: boolean) => canvas.portGlobal(nodeId, port, isOutput),
+      nodeAt: (nodeId: string) => canvas.nodeGlobal(nodeId),
+      edgeAt: (edgeId: string) => canvas.edgeGlobal(edgeId),
+      label: (nodeId: string) => canvas.nodeLabel(nodeId),
+      problem: (nodeId: string) => canvas.nodeProblem(nodeId),
+      fitAt: () => centreOf(routingEditor.fitButton),
+      /** The loudest sample on each side of these buses of the mix, tapped on first asking (#359). */
+      peaks: (names: string[]) => Object.fromEntries(soundLibrary.busPeaks(names)),
+      buses: () => soundLibrary.busLevels(),
+    },
+  };
+}

src/editor/debugHook.ts

@@ -16,6 +16,7 @@ import { saturationAutoGain } from '../core/soundfx/saturation';
 import { curveHooks } from './debug/curveHooks';
 import { soundHooks } from './debug/soundHooks';
 import { patternHooks } from './debug/patternHooks';
+import { routingHooks } from './debug/routingHooks';
 import { songHooks } from './debug/songHooks';
 import { documentHooks } from './debug/documentHooks';
 import { graphHooks } from './debug/graphHooks';
@@ -50,6 +51,7 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
     ...curveHooks(context),
     ...patternHooks(context),
     ...songHooks(context),
+    ...routingHooks(context),
     ...soundHooks(context),
     ...renderHooks(context),
     /**

src/editor/graph/GraphCanvas.ts

@@ -26,14 +26,16 @@ import {
   soundFxParamsMismatch,
   startStateOf,
 } from '../../core/graph';
-import type { GraphAsset } from '../../core/model/Asset';
 import { graphLookup } from '../../core/model/graphLookup';
 import { particleLibrary } from '../../viewport/ParticleLibrary';
 import { shaderLibrary } from '../../viewport/ShaderLibrary';
 import { soundFxBuildFor } from '../../core/soundfx/compile';
 import { instrumentCheck, instrumentSourcesOf } from '../../core/instrument/compile';
+import { masterRoutingProblems } from '../../core/music/projectRouting';
 import { routingProblems } from '../../core/music/routing';
-import { findAsset, findGraphAsset } from '../../core/model/Project';
+import { ROUTED_ASSET } from '../../core/music/routingNodes';
+import { hasAssetEditor } from '../assetTabs';
+import { findAsset, findGraphAsset, type GraphHolder } from '../../core/model/Project';
 import { type Trace, TRACE_FADE } from '../../runtime/systems/BehaviorSystem';
 import { ViewTween } from '../viewTween';
 import { BeadClock } from './beads';
@@ -281,7 +283,7 @@ export class GraphCanvas extends Widget {
     return { w: Math.max(this.minWidth, 200), h: Math.max(this.minHeight, 200) };
   }
 
-  private asset(): GraphAsset | null {
+  private asset(): GraphHolder | null {
     return (this.assetId && findGraphAsset(this.state.project, this.assetId)) || null;
   }
 
@@ -316,7 +318,9 @@ export class GraphCanvas extends Widget {
               ? instrumentCheck(asset, instrumentSourcesOf(this.state.project)).problems
               : asset.type === 'song'
                 ? routingProblems(asset.graph)
-                : null;
+                : asset.type === 'routing'
+                  ? masterRoutingProblems(asset.graph)
+                  : null;
     for (const node of asset.graph.nodes) {
       const resolved = resolveDef(node, asset.graph, lookup);
       if (!resolved) continue;
@@ -429,7 +433,7 @@ export class GraphCanvas extends Widget {
    * one held by the selected object's instance. Without a selection nothing is strong – that keeps
    * "many instances, many states" readable instead of picking one of them at random.
    */
-  private stateMarks(asset: GraphAsset): Map<string, 'held' | 'current'> {
+  private stateMarks(asset: GraphHolder): Map<string, 'held' | 'current'> {
     const marks = new Map<string, 'held' | 'current'>();
     if (asset.type !== 'statemachine') return marks;
     const selection = this.state.selection;
@@ -665,6 +669,13 @@ export class GraphCanvas extends Widget {
   }
 
   private openCalledBehavior(node: GraphNode): boolean {
+    // A node of the master routing (#351) stands for its asset; a bus has no tab, its node shows it already.
+    if (node.type === ROUTED_ASSET) {
+      const asset = findAsset(this.state.project, node.id);
+      if (!asset || !hasAssetEditor(asset.type)) return false;
+      this.state.openAsset(node.id);
+      return true;
+    }
     if (node.type === SHADER_CALL || node.type === INSTRUMENT_SOUND_FX) {
       const shader = node.type === SHADER_CALL;
       const id = textOf(node.params[shader ? FUNCTION_PARAM : 'fx'] ?? '');

src/editor/graph/graphHost.ts

@@ -1,5 +1,5 @@
 import type { AddNodeCommand } from '../../core/commands/graphCommands';
-import type { GraphAsset } from '../../core/model/Asset';
+import type { GraphHolder } from '../../core/model/Project';
 import type { Box } from '../framing';
 import type { EditorState } from '../state';
 import type { NodeView } from './NodeView';
@@ -11,7 +11,7 @@ export interface GraphCanvasHost {
   readonly state: EditorState;
   /** The asset on the canvas; empty when there is none. */
   assetId(): string;
-  asset(): GraphAsset | null;
+  asset(): GraphHolder | null;
   views(): ReadonlyMap<string, NodeView>;
   /** Views in stacking order, topmost first – a node drawn over another one wins the pointer. */
   topDownViews(): Iterable<NodeView>;

src/editor/graph/paletteEntries.ts

@@ -21,11 +21,11 @@ import {
   STATE_NAME_PARAM,
   terminalNode,
 } from '../../core/graph';
-import type { GraphAsset, ShaderAsset, ShaderFunctionAsset } from '../../core/model/Asset';
+import type { ShaderAsset, ShaderFunctionAsset } from '../../core/model/Asset';
 import { FIND, FIND_MODE } from '../../core/graph/findBlock';
 import { graphLookup } from '../../core/model/graphLookup';
 import type { PropertyBag } from '../../core/model/Properties';
-import type { Project } from '../../core/model/Project';
+import type { GraphHolder, Project } from '../../core/model/Project';
 import {
   isParticlePropertyNode,
   PARTICLE_PROPERTY,
@@ -132,14 +132,14 @@ function shaderEntries(project: Project, asset: ShaderAsset | ShaderFunctionAsse
  * generic "Run behavior" – and once more as the event "On <name>" if it has an End to be heard
  * through (#294) –, and the two terminals drop out once the graph has them.
  */
-export function paletteEntries(project: Project, asset: GraphAsset): PaletteEntry[] {
+export function paletteEntries(project: Project, asset: GraphHolder): PaletteEntry[] {
   if (asset.type === 'statemachine') {
     const params = { [STATE_NAME_PARAM]: nextStateName(asset.graph) };
     return [{ id: State.type, hint: State.category, def: State, params }];
   }
   if (asset.type === 'shader' || asset.type === 'shaderfunction') return shaderEntries(project, asset);
-  // A song's routing holds the nodes of its tracks and its output, which come and go on their own (#350).
-  if (asset.type === 'song') return [];
+  // A routing holds nodes that come and go on their own: a song's tracks (#350), the assets (#351).
+  if (asset.type === 'song' || asset.type === 'routing') return [];
   if (asset.type === 'soundfx') {
     const placed = new Set(asset.graph.nodes.map((n) => n.type));
     return SOUND_FX_NODES.filter(

src/editor/inspector/Inspector.ts

@@ -17,7 +17,9 @@ import {
   objectSignature,
   refreshObjectSection,
 } from './objectSection';
+import { buildRoutingNodeSection, refreshRoutingNodeSection, routingNodeSignature } from './routingSection';
 import { buildSongSection, refreshSongSection, songSignature } from './songSection';
+import { ROUTING_ID } from '../../core/model/Project';
 import { buildTrackSection, refreshTrackSection, trackSignature } from './trackSection';
 import { INLINE_LIMIT } from '../variables/target';
 import { inlineListsIn } from '../variables/VariablesEditor';
@@ -130,6 +132,7 @@ export class Inspector extends Panel {
         new Label('Select an asset, a scene object or a node.', { style: 'muted', wrap: true }),
       );
     else if (s.kind === 'asset') buildAssetSection(this.host, s.assetId);
+    else if (s.kind === 'node' && s.assetId === ROUTING_ID) buildRoutingNodeSection(this.host, s.nodeId);
     else if (s.kind === 'node') buildNodeSection(this.host, s.assetId, s.nodeId);
     else if (s.kind === 'frame') buildFrameSection(this.host, s.assetId, s.frameId);
     else if (s.kind === 'clip') buildClipSection(this.host, s.assetId, s.clipId);
@@ -147,6 +150,8 @@ export class Inspector extends Panel {
     const s = this.state.selection;
     if (!s) return '';
     if (s.kind === 'asset') return assetSignature(this.state.project, s.assetId);
+    if (s.kind === 'node' && s.assetId === ROUTING_ID)
+      return routingNodeSignature(this.state.project, s.nodeId);
     if (s.kind === 'node') return nodeSignature(this.state.project, s.assetId, s.nodeId);
     if (s.kind === 'frame') return frameSignature(this.state.project, s.assetId, s.frameId);
     if (s.kind === 'clip') return clipSignature(this.state.project, s.assetId, s.clipId);
@@ -176,23 +181,25 @@ export class Inspector extends Panel {
     const ok =
       s.kind === 'asset'
         ? refreshAssetSection(this.host, s.assetId)
-        : s.kind === 'node'
-          ? refreshNodeSection(this.host, s.assetId, s.nodeId)
-          : s.kind === 'frame'
-            ? refreshFrameSection(this.host, s.assetId, s.frameId)
-            : s.kind === 'clip'
-              ? refreshClipSection(this.host, s.assetId, s.clipId)
-              : s.kind === 'shape'
-                ? refreshShapeSection(this.host, s.assetId, s.shapeId)
-                : s.kind === 'annotation'
-                  ? refreshAnnotationSection(this.host, s.assetId, s.annotationId)
-                  : s.kind === 'track'
-                    ? refreshTrackSection(this.host, s.assetId, s.trackId, s.keys)
-                    : s.kind === 'edge'
-                      ? refreshEdgeSection(this.host, s.assetId, s.edgeId)
-                      : s.kind === 'song'
-                        ? refreshSongSection(this.host, s.assetId, s.trackId, s.itemIds)
-                        : s.objectIds.length > 1 || refreshObjectSection(this.host, s.holderId, s.objectId);
+        : s.kind === 'node' && s.assetId === ROUTING_ID
+          ? refreshRoutingNodeSection(this.host, s.nodeId)
+          : s.kind === 'node'
+            ? refreshNodeSection(this.host, s.assetId, s.nodeId)
+            : s.kind === 'frame'
+              ? refreshFrameSection(this.host, s.assetId, s.frameId)
+              : s.kind === 'clip'
+                ? refreshClipSection(this.host, s.assetId, s.clipId)
+                : s.kind === 'shape'
+                  ? refreshShapeSection(this.host, s.assetId, s.shapeId)
+                  : s.kind === 'annotation'
+                    ? refreshAnnotationSection(this.host, s.assetId, s.annotationId)
+                    : s.kind === 'track'
+                      ? refreshTrackSection(this.host, s.assetId, s.trackId, s.keys)
+                      : s.kind === 'edge'
+                        ? refreshEdgeSection(this.host, s.assetId, s.edgeId)
+                        : s.kind === 'song'
+                          ? refreshSongSection(this.host, s.assetId, s.trackId, s.itemIds)
+                          : s.objectIds.length > 1 || refreshObjectSection(this.host, s.holderId, s.objectId);
     if (!ok) this.rebuild();
   }
 }

src/editor/inspector/edgeSection.ts

@@ -3,11 +3,13 @@ import { SetSendCommand } from '../../core/commands/songCommands';
 import {
   type EdgeSend,
   findNode,
+  type Graph,
   type GraphEdge,
   isStateNode,
   resolveDef,
   stateName,
 } from '../../core/graph';
+import { routedKind, sendsTapped } from '../../core/music/projectRouting';
 import { SEND_TAPS, sendOf } from '../../core/music/routing';
 import { TRACK_MAX_DB, TRACK_MIN_DB } from '../../core/music/song';
 import type { PropertyDef } from '../../core/properties/PropertySchema';
@@ -47,15 +49,18 @@ export interface EdgeDescription {
   /** What flows through it, as the output names it. */
   type: string;
   name: string;
-  /** On a link of a song's routing (#350): what it sends; null on any other link. */
+  /** On a link of a song's routing (#350) or of the master routing (#351): what it sends; null on any other link. */
   send: EdgeSend | null;
+  /** Whether the link may take the sound anywhere but after the level: not out of a sound, an instrument or a pattern. */
+  tapped: boolean;
 }
 
 /** Null when the link is gone. An end whose node or port is gone reads `?`. */
 export function describeEdge(project: Project, assetId: string, edgeId: string): EdgeDescription | null {
-  const graph = findGraphAsset(project, assetId)?.graph;
+  const holder = findGraphAsset(project, assetId);
+  const graph = holder?.graph;
   const edge = graph?.edges.find((e) => e.id === edgeId);
-  if (!graph || !edge) return null;
+  if (!holder || !graph || !edge) return null;
   const lookup = graphLookup(project);
   const end = (side: GraphEdge['from'], ports: 'inputs' | 'outputs') => {
     const node = findNode(graph, side.node);
@@ -78,10 +83,17 @@ export function describeEdge(project: Project, assetId: string, edgeId: string):
     input: to.port,
     type: from.type,
     name: edge.label ?? '',
-    send: findGraphAsset(project, assetId)?.type === 'song' ? sendOf(edge) : null,
+    send: holder.type === 'song' || holder.type === 'routing' ? sendOf(edge) : null,
+    tapped: holder.type === 'song' || sendsTapped(fromKind(graph, edge)),
   };
 }
 
+/** The asset type a link of the master routing (#351) comes out of; `''` for anything else. */
+function fromKind(graph: Graph, edge: GraphEdge): string {
+  const node = findNode(graph, edge.from.node);
+  return node ? routedKind(node) : '';
+}
+
 /** Structure of a link selection: how many, and for one of them what it joins. */
 export function edgeSignature(
   project: Project,
@@ -140,15 +152,19 @@ export function buildEdgeSection(
       onInput: () => {},
       onChange: (next) => set({ volume: Number(next) }),
     });
+    host.fields.set(SEND_VOLUME.key, volume);
+    host.body.add(volume.row);
+    if (!d.tapped) {
+      addNote(host, 'In decibels, after the volume and the sound FX of the asset.', 'small');
+      return;
+    }
     const tap = createFieldRow(host, SEND_TAP, send.tap, {
       onInput: () => {},
       onChange: (next) => set({ tap: SEND_TAPS.find((t) => t.value === textOf(next))?.value ?? 'post' }),
     });
-    host.fields.set(SEND_VOLUME.key, volume);
     host.fields.set(SEND_TAP.key, tap);
-    host.body.add(volume.row);
     host.body.add(tap.row);
-    addNote(host, 'In decibels. Mode says where on its track the link takes the sound.', 'small');
+    addNote(host, 'In decibels. Mode says where on its track or bus the link takes the sound.', 'small');
   } else {
     fact('Input', d.input);
     fact('Type', d.type);

src/editor/inspector/fieldFactory.ts

@@ -20,7 +20,7 @@ import {
   soundEntries,
 } from '../../core/properties/assetRef';
 import { NO_FX } from '../../core/properties/assetFx';
-import { busesInto, MASTER_BUS } from '../../core/properties/buses';
+import { MASTER_BUS } from '../../core/properties/buses';
 import { keyName } from '../../core/keys';
 import { FIRST_TILE_LAYER } from '../../core/model/liveTilemap';
 import { type ObjectChoice, objectReference, referencedId } from '../../core/model/objectRefs';
@@ -403,19 +403,15 @@ const REFERENCES: Record<ReferenceKind, Reference> = {
     label: assetRefLabel,
     choices: (project, def) => {
       const extras = def.kind === 'asset' ? def : undefined;
-      // Asked as the menu opens: another bus may have been sent into this one meanwhile.
-      const left = new Set(extras?.intoFor ? busesInto(project, extras.intoFor) : []);
       return [
         ...(extras?.master ? [{ id: MASTER_BUS, label: MASTER_LABEL }] : []),
         ...(extras?.noFx ? [{ id: NO_FX, label: NO_ASSET_LABEL }] : []),
-        ...assetRefChoices(project, extras?.assetTypes)
-          .filter((asset) => !left.has(asset.id))
-          .flatMap((asset) =>
-            // A sound with its clips (#357), each as "Kick / Clip 1 (sound)".
-            asset.type === 'sound'
-              ? soundEntries(asset).map((entry) => ({ id: entry.id, label: `${entry.label} (sound)` }))
-              : [{ id: asset.id, label: assetChoiceLabel(asset) }],
-          ),
+        ...assetRefChoices(project, extras?.assetTypes).flatMap((asset) =>
+          // A sound with its clips (#357), each as "Kick / Clip 1 (sound)".
+          asset.type === 'sound'
+            ? soundEntries(asset).map((entry) => ({ id: entry.id, label: `${entry.label} (sound)` }))
+            : [{ id: asset.id, label: assetChoiceLabel(asset) }],
+        ),
       ];
     },
   },

src/editor/inspector/nodeSection.ts

@@ -26,9 +26,8 @@ import {
   TRANSITION_PARAM,
   variablesSourceOf,
 } from '../../core/graph';
-import type { GraphAsset } from '../../core/model/Asset';
 import { graphLookup } from '../../core/model/graphLookup';
-import { findAssetOf, findGraphAsset, type Project } from '../../core/model/Project';
+import { findAssetOf, findGraphAsset, type GraphHolder, type Project } from '../../core/model/Project';
 import { type PropertyValue, textOf } from '../../core/model/Properties';
 import {
   isListNode,
@@ -106,7 +105,7 @@ function farStateName(graph: Graph, edge: GraphEdge, nodeId: string): string {
 }
 
 /** A state machine declares no variables; its one node type has none to name. */
-const variablesOf = (asset: GraphAsset): PropertyDef[] => (asset.type === 'behavior' ? asset.variables : []);
+const variablesOf = (asset: GraphHolder): PropertyDef[] => (asset.type === 'behavior' ? asset.variables : []);
 
 /** Description, settings (params) and the inline values of unconnected data inputs. */
 export function buildNodeSection(host: InspectorHost, assetId: string, nodeId: string): void {

src/editor/inspector/routingSection.ts

@@ -0,0 +1,62 @@
+import { SetMasterFxCommand, SetMasterVolumeCommand } from '../../core/commands/projectCommands';
+import { findAsset, type Project } from '../../core/model/Project';
+import { textOf } from '../../core/model/Properties';
+import { MASTER_BUS } from '../../core/properties/buses';
+import type { PropertyDef } from '../../core/properties/PropertySchema';
+import { assetSignature, buildAssetSection, refreshAssetSection } from './assetSection';
+import { createFieldRow } from './fieldFactory';
+import { addNote, addTitle, type InspectorHost } from './host';
+
+const MASTER_VOLUME: PropertyDef = {
+  key: 'master-volume',
+  label: 'Volume',
+  kind: 'number',
+  default: 1,
+  min: 0,
+  max: 1,
+  step: 0.05,
+};
+const MASTER_FX: PropertyDef = {
+  key: 'master-fx',
+  label: 'Sound FX',
+  kind: 'asset',
+  default: '',
+  assetTypes: ['soundfx'],
+};
+
+/**
+ * A node of the master routing (#351) stands for its asset, and the inspector shows that asset as
+ * the asset panel would; the master shows its volume and sound FX, those of the project settings.
+ */
+export function buildRoutingNodeSection(host: InspectorHost, nodeId: string): void {
+  if (nodeId !== MASTER_BUS) return buildAssetSection(host, nodeId);
+  const project = host.state.project;
+  addTitle(host, 'MASTER');
+  const volume = createFieldRow(host, MASTER_VOLUME, project.masterVolume, {
+    onInput: () => {},
+    onChange: (next) => void host.state.execute(new SetMasterVolumeCommand(Number(next))),
+  });
+  const fx = createFieldRow(host, MASTER_FX, project.masterFx, {
+    onInput: () => {},
+    onChange: (next) => void host.state.execute(new SetMasterFxCommand(textOf(next))),
+  });
+  host.fields.set(MASTER_VOLUME.key, volume);
+  host.fields.set(MASTER_FX.key, fx);
+  host.body.add(volume.row);
+  host.body.add(fx.row);
+  addNote(host, 'Where the game is heard. The same as in Project settings.', 'small');
+}
+
+export function routingNodeSignature(project: Project, nodeId: string): string {
+  if (nodeId === MASTER_BUS) return 'master';
+  return findAsset(project, nodeId) ? assetSignature(project, nodeId) : 'missing';
+}
+
+/** False when the node's asset is gone (rebuild). */
+export function refreshRoutingNodeSection(host: InspectorHost, nodeId: string): boolean {
+  if (nodeId !== MASTER_BUS) return refreshAssetSection(host, nodeId);
+  const project = host.state.project;
+  host.fields.get(MASTER_VOLUME.key)?.setValue(project.masterVolume);
+  host.fields.get(MASTER_FX.key)?.setValue(project.masterFx);
+  return true;
+}

src/editor/pattern/PatternEditor.ts

@@ -24,7 +24,7 @@ import { DEFAULT_TEMPO } from '../../core/music/time';
 import { instrumentFx, playNote } from '../../runtime/systems/behaviorContext';
 import { Button, Dropdown, Label, Menu, type Widget } from '../../ui';
 import { Music } from '../../viewport/music';
-import { playedBus } from '../../core/music/mixer';
+import { playedRoute } from '../../core/music/mixer';
 import { soundLibrary } from '../../viewport/SoundLibrary';
 import { AssetTabEditor } from '../AssetTabEditor';
 import { claimTransport, releaseTransport } from '../music/transport';
@@ -54,10 +54,10 @@ export class PatternEditor extends AssetTabEditor<PatternAsset, PianoRoll> {
   readonly ghostsButton: Button;
   /** Where the ghost notes come from: song, track and bar. */
   readonly ghostSource = new Label('', { style: 'muted' });
-  /** Heard through the sound FX (#352) and on the bus of the asset and the master, as in the game (#325). */
+  /** Heard through the sound FX (#352) and along the routing of the asset (#351), as in the game. */
   readonly music = new Music(
     () => this.state.project,
-    () => playedBus(this.state.project, '', this.asset()?.props ?? {}),
+    () => playedRoute(this.state.project, '', this.asset()?.id ?? ''),
     () => {
       const asset = this.asset();
       return asset && fxVoiceOf(this.state.project, assetFxOf(asset.props), patternTempo(asset.props));

src/editor/routing/RoutingEditor.ts

@@ -0,0 +1,63 @@
+import { masterRoutingProblems } from '../../core/music/projectRouting';
+import { ROUTING_ID } from '../../core/model/Project';
+import { Button, Label, Spacer, VStack } from '../../ui';
+import { GraphCanvas } from '../graph/GraphCanvas';
+import { SnapToggle } from '../graph/SnapToggle';
+import type { EditorState } from '../state';
+import { TabHeader } from '../TabHeader';
+
+const INFO_WIDTH = 220;
+
+/**
+ * The Master routing tab (#351), one per project: a node per sound, instrument, pattern, song and bus
+ * and the master, the links between them where each one goes. Edited as the routing of a song is
+ * (#350); a click on a node shows its asset in the inspector, a double click opens it.
+ */
+export class RoutingEditor extends VStack {
+  readonly canvas: GraphCanvas;
+  readonly fitButton: Button;
+  readonly snap: SnapToggle;
+  private readonly info = new Label('', { style: 'small', align: 'right' });
+
+  constructor(private readonly state: EditorState) {
+    super();
+    this.canvas = new GraphCanvas(state, 'routing');
+    this.snap = new SnapToggle(() => this.canvas);
+    this.fitButton = new Button('Fit', { onClick: () => this.canvas.fit() });
+    this.info.minWidth = INFO_WIDTH;
+    const header = new TabHeader();
+    for (const widget of this.snap.widgets) header.add(widget);
+    header.add(this.fitButton);
+    header.add(new Spacer(), 1);
+    header.add(this.info);
+    this.add(header);
+    this.add(this.canvas, 1);
+    state.on('project', () => this.refresh());
+    state.on('load', () => this.close());
+  }
+
+  /** Shows the routing of the project; framed the first time, as it was left after that. */
+  open(): void {
+    this.canvas.show(ROUTING_ID);
+    this.refresh();
+  }
+
+  /** The tab is closed: opened again, the routing starts from a fitted view. */
+  close(): void {
+    this.canvas.show('');
+    this.refresh();
+  }
+
+  /** The readout: how many links, and how many nodes go nowhere and are never heard. */
+  get shownInfo(): string {
+    return this.info.text;
+  }
+
+  private refresh(): void {
+    if (this.canvas.currentAssetId !== ROUTING_ID) return this.info.setText('');
+    const graph = this.state.project.routing;
+    const silent = Object.keys(masterRoutingProblems(graph)).length;
+    const links = `${graph.edges.length} link${graph.edges.length === 1 ? '' : 's'}`;
+    this.info.setText(silent > 0 ? `${links} · ${silent} going nowhere` : links);
+  }
+}

src/editor/song/SongEditor.ts

@@ -27,7 +27,7 @@ import { assetFxOf } from '../../core/properties/assetFx';
 import type { SoundStore } from '../../core/store/SoundStore';
 import { Button, Dialog, Dropdown, Label, Menu, ui, VStack, type Widget } from '../../ui';
 import { Music } from '../../viewport/music';
-import { playedBus } from '../../core/music/mixer';
+import { playedRoute } from '../../core/music/mixer';
 import { soundLibrary } from '../../viewport/SoundLibrary';
 import {
   type InputDevice,
@@ -92,10 +92,10 @@ export class SongEditor extends AssetTabEditor<SongAsset, SongTimeline> {
   readonly snap = new SnapToggle(() => this.routing);
   private shown: SongView = 'timeline';
   private readonly pane = new VStack();
-  /** Heard through the sound FX (#352) and on the bus of the asset and the master, as in the game (#325). */
+  /** Heard through the sound FX (#352) and along the routing of the asset (#351), as in the game. */
   readonly music = new Music(
     () => this.state.project,
-    () => playedBus(this.state.project, '', this.asset()?.props ?? {}),
+    () => playedRoute(this.state.project, '', this.asset()?.id ?? ''),
     () => {
       const asset = this.asset();
       return asset && fxVoiceOf(this.state.project, assetFxOf(asset.props), songTempo(asset.props));

src/editor/sound/SoundEditor.ts

@@ -152,8 +152,8 @@ export class SoundEditor extends AssetTabEditor<SoundAsset, WaveCanvas> {
     this.stop();
     claimTransport(this.halt);
     const props = resolveAssetProps(this.state.project, asset);
-    // Through its sound FX (#352), its bus and the master, as the game hears it (#325).
-    const bus = playedBus(this.state.project, '', props);
+    // Through its sound FX (#352) and along its routing (#351), as the game hears it.
+    const bus = playedBus(this.state.project, '', asset.id);
     const fx = fxVoiceOf(this.state.project, assetFxOf(props), DEFAULT_TEMPO) ?? DRY_VOICE;
     const file = playedSoundOf({ asset, clip });
     this.voice = soundLibrary.play(file, volumeOf(props), false, PREVIEW_OWNER, fx, bus);

src/editor/soundfx/SoundFxEditor.ts

@@ -106,8 +106,8 @@ export class SoundFxEditor extends AssetTabEditor<SoundFxAsset, GraphCanvas> {
     if (!sound?.asset.file || !plan) return;
     const props = resolveAssetProps(this.state.project, sound.asset);
     const fx = { plan, params: { ...this.values } };
-    // On the bus of the sound, as the game would play it there (#325).
-    const bus = playedBus(this.state.project, '', props);
+    // Along the routing of the sound, as the game would play it there (#351).
+    const bus = playedBus(this.state.project, '', sound.asset.id);
     const file = playedSoundOf(sound);
     const voice = soundLibrary.play(file, volumeOf(props), false, PREVIEW_OWNER, fx, bus);
     if (voice) this.voices.push(voice);

src/editor/state.ts

@@ -28,6 +28,8 @@ import type { GameScale, PlayFrom } from '../core/model/playSettings';
 import type { PlaceableAssetType } from '../core/model/AssetTypes';
 import type { VisibilityPart } from '../core/model/sceneVisibility';
 import type { ValuePath } from '../core/properties/valuePath';
+import { KeepRoutingCommand } from '../core/commands/routingCommands';
+import { settleRouting } from '../core/music/projectRouting';
 
 export type Selection =
   | { kind: 'asset'; assetId: string }
@@ -310,6 +312,8 @@ export class EditorState {
     this.paused = false;
     this.project = project;
     this.revision = revision;
+    // Every sound, instrument, pattern, song and bus has its node in the Master routing (#351).
+    settleRouting(project);
     this.commands = new CommandStack(project);
     this.selection = null;
     this.openedValues = null;
@@ -409,7 +413,7 @@ export class EditorState {
    */
   execute(command: Command): boolean {
     return this.runEdit(() => {
-      this.commands.execute(command);
+      this.commands.execute(new KeepRoutingCommand(command));
       return true;
     });
   }

src/runtime/systems/behaviorContext.ts

@@ -31,8 +31,9 @@ import {
   songTempo,
   SOUND_ITEM_MAX_DB,
 } from '../../core/music/song';
+import type { SequencePlay } from '../../core/music/playbacks';
 import { songBuses } from '../../core/music/songBuses';
-import { playedBus, reachedBus } from '../../core/music/mixer';
+import { type MixRoute, playedBus, playedRoute, reachedBus } from '../../core/music/mixer';
 import { DRY_VOICE, type FxParams, type FxVoice } from '../../core/soundfx/nodes';
 import type { Entity } from '../Entity';
 import { PhysicsSystem } from '../physics/PhysicsSystem';
@@ -295,7 +296,7 @@ function playSound(
     loop ?? loopsOf(props),
     owner,
     fx ?? DRY_VOICE,
-    playedBus(project, bus, props),
+    playedBus(project, bus, ref.asset.id),
   );
 }
 
@@ -306,7 +307,7 @@ export function instrumentFx(project: Project, instrumentId: string, picked: str
 
 /** The bus of the mix a note of that instrument is heard on, by the pick of a node (#325). */
 export function instrumentBus(project: Project, instrumentId: string, picked: string): string {
-  return playedBus(project, picked, findAssetOf(project, instrumentId, 'instrument')?.props ?? {});
+  return playedBus(project, picked, instrumentId);
 }
 
 /**
@@ -357,6 +358,11 @@ export function instrumentVoiceName(instrumentId: string): string {
   return `instrument:${instrumentId}`;
 }
 
+/** Where a playing of a pattern or a song goes: into one bus, or along its links (#351). */
+function heardOn(route: MixRoute): Pick<SequencePlay, 'bus' | 'sends'> {
+  return typeof route === 'string' ? { bus: route } : { sends: route };
+}
+
 /**
  * A pattern played by a game: its notes through its instrument at its tempo, the whole of it once or
  * round and round – the loop set on its ruler is for editing. Its notes take the volume and the owner
@@ -390,7 +396,7 @@ function playPattern(
       loop: loop ? { start: 0, end: length } : null,
       needs: sequenceNeeds(project, sequence),
       ...(fx && { fx }),
-      bus: playedBus(project, bus, asset.props),
+      ...heardOn(playedRoute(project, bus, patternId)),
       strike: (note) => strikeNote({ project, audio }, { ...note, volume: level }, owner),
     },
     owner,
@@ -431,7 +437,7 @@ function playSong(
       fadeIn: heldFade(fadeIn),
       buses: songBuses(project, song),
       ...(fx && { fx }),
-      bus: playedBus(project, bus, song.props),
+      ...heardOn(playedRoute(project, bus, songId)),
       strike: (note) => strikeNote({ project, audio }, note, owner),
       strikeClip: (clip) => playClip({ project, audio }, clip),
     },

src/viewport/SoundLibrary.ts

@@ -35,7 +35,7 @@ import type { EaseShare } from '../core/model/animation';
 import { type BusLevel, Playbacks, type SequenceNeeds, type SequencePlay } from '../core/music/playbacks';
 import { arrivalOf, sendDelays, type TimedBus } from '../core/music/routing';
 import type { SendTap } from '../core/graph/Graph';
-import { MASTER_MIX, type MixBus, sameMix } from '../core/music/mixer';
+import { MASTER_MIX, type MixBus, type MixSend, sameMix } from '../core/music/mixer';
 import { limiterLatency } from '../core/soundfx/dynamics';
 import type { ScheduledClip, ScheduledNote } from '../core/music/Scheduler';
 import { dbToGain, SOUND_ITEM_MAX_DB } from '../core/music/song';
@@ -632,6 +632,7 @@ export class SoundLibrary implements AudioSink {
     this.cutPan(bus);
     bus.pan.connect(this.outOf(target));
     bus.into = target;
+    this.alignSends();
   }
 
   /**
@@ -714,9 +715,10 @@ export class SoundLibrary implements AudioSink {
   private async applyMix(): Promise<void> {
     const names = new Set(this.mix.map((bus) => bus.name));
     const waits: Promise<void>[] = [];
-    for (const { name, volume, into, fx } of this.mix) {
+    for (const { name, volume, into, sends, fx } of this.mix) {
       const bus = this.bus(name, into);
-      this.route(name, bus, into);
+      if (sends) this.setSends(bus, sends);
+      else this.route(name, bus, into);
       this.glideLevel(bus, this.mixVolumes.get(name) ?? volume);
       waits.push(this.setFx(bus, fx));
     }
@@ -943,7 +945,7 @@ export class SoundLibrary implements AudioSink {
     if (play.sequence.notes.length === 0 && !play.sequence.clips?.length) return 0;
     const id = this.nextId++;
     const buses = play.buses ?? [];
-    this.open(id, buses, play.fx ?? null, play.bus ?? MASTER_MIX);
+    this.open(id, buses, play.fx ?? null, play.bus ?? MASTER_MIX, play.sends);
     const tracks = new Set(buses.map((bus) => bus.name));
     const into = (bus: string | undefined) => groupBus(id, bus !== undefined && tracks.has(bus) ? bus : '');
     const { strike, strikeClip } = play;
@@ -992,14 +994,22 @@ export class SoundLibrary implements AudioSink {
 
   /**
    * The buses of a playing, its tracks into its master and a pattern item's into its track (#346),
-   * each with the sound FX it was given. Their chains are made once the worklet is there (`ready`).
+   * each with the sound FX it was given; its master into `into`, or along `sends` (#351). Their
+   * chains are made once the worklet is there (`ready`).
    */
-  private open(id: number, tracks: readonly BusLevel[], fx: FxVoice | null, into: string): void {
+  private open(
+    id: number,
+    tracks: readonly BusLevel[],
+    fx: FxVoice | null,
+    into: string,
+    sends?: readonly MixSend[],
+  ): void {
     const masterName = groupBus(id, '');
     const master = this.bus(masterName, into);
     master.gain.gain.value = 0;
     master.set = { gain: 0, pan: 0 };
     master.fx = fx;
+    if (sends) this.setSends(master, sends);
     const names = new Set(tracks.map((track) => track.name));
     const inside = (bus: string | undefined) =>
       bus !== undefined && names.has(bus) ? groupBus(id, bus) : masterName;

src/viewport/music.ts

@@ -5,7 +5,7 @@ import {
   type SchedulerOptions,
 } from '../core/music/Scheduler';
 import { sequenceNeeds } from '../core/music/needs';
-import { MASTER_MIX } from '../core/music/mixer';
+import { MASTER_MIX, type MixRoute } from '../core/music/mixer';
 import type { BusLevel } from '../core/music/playbacks';
 import type { Sequence } from '../core/music/sequence';
 import type { Project } from '../core/model/Project';
@@ -52,13 +52,13 @@ export class Music {
   readonly clips: PlannedClip[] = [];
 
   /**
-   * `output` is the bus of the mix what it plays is heard on (#325): that of the pattern or song in
-   * the tab, so it sounds as it would in the game. The master where left out. `fx` is the sound FX of
+   * `output` is where what it plays goes (#351): along the routing of the pattern or song in the
+   * tab, so it sounds as it would in the game. The master where left out. `fx` is the sound FX of
    * that pattern or song (#352), on the way there.
    */
   constructor(
     private readonly project: () => Project,
-    private readonly output: () => string = () => MASTER_MIX,
+    private readonly output: () => MixRoute = () => MASTER_MIX,
     private readonly fx: () => FxVoice | null = () => null,
   ) {}
 
@@ -104,12 +104,14 @@ export class Music {
 
   /**
    * Where what goes to the output of the pattern or song is heard: its own bus, set to its sound FX
-   * as it is now and on into `output`. A key of the roll is played there too.
+   * as it is now and on along `output`. A key of the roll is played there too.
    */
   heardOn(): string {
     const fx = this.fx();
+    const output = this.output();
+    const route = typeof output === 'string' ? { into: output } : { sends: output };
     this.fxReady = soundLibrary.setBuses([
-      { name: this.outBus, gain: 1, pan: 0, into: this.output(), ...(fx && { fx }) },
+      { name: this.outBus, gain: 1, pan: 0, ...route, ...(fx && { fx }) },
     ]);
     return this.outBus;
   }

tests/core/asset-fx.test.ts

@@ -128,10 +128,10 @@ function gains(layer: FxPlan | undefined): number[] {
 }
 
 describe('the Sound FX row (#352)', () => {
-  it('stands right before Bus on a sound, an instrument, a pattern and a song', () => {
+  it('stands last on a sound, an instrument, a pattern and a song, where Bus stood before #351', () => {
     for (const type of ['sound', 'instrument', 'pattern', 'song'] as AssetType[]) {
       const keys = schemaFor(type).map((def) => def.key);
-      expect(keys.indexOf(ASSET_FX_KEY), type).toBe(keys.indexOf('bus') - 1);
+      expect(keys.indexOf(ASSET_FX_KEY), type).toBe(keys.length - 1);
       expect(schemaFor(type).find((def) => def.key === ASSET_FX_KEY)).toMatchObject({
         kind: 'asset',
         default: '',

tests/core/buses.test.ts

@@ -1,6 +1,6 @@
 /**
- * Master and buses (#325): which bus a bus goes into, what the sound library is set up with, and
- * which bus a sound, a note, a pattern or a song is heard on.
+ * Master and buses (#325): what the sound library is set up with, and which bus a sound, a note, a
+ * pattern or a song is heard on – where each goes is the master routing's (#351).
  */
 import { describe, expect, it } from 'vitest';
 import {
@@ -21,7 +21,7 @@ import {
   reachedBus,
   sameMix,
 } from '../../src/core/music/mixer';
-import { BUS_INTO_KEY, BUS_KEY, busesInto, busInto, MASTER_BUS } from '../../src/core/properties/buses';
+import { MASTER_BUS } from '../../src/core/properties/buses';
 import { schemaForAsset } from '../../src/core/properties/PropertySchema';
 import type { FxParams, FxVoice } from '../../src/core/soundfx/nodes';
 import { GameRun } from '../../src/runtime/GameRun';
@@ -34,6 +34,7 @@ import {
   makeSpriteScene,
   place,
   roundTrip,
+  routingOf,
   startWorld,
 } from '../helpers';
 
@@ -46,9 +47,8 @@ function withBuses(...names: string[]) {
     f.stack.execute(command);
     return command.asset.id;
   });
-  const into = (bus: string, target: string) =>
-    f.stack.execute(new SetAssetPropertyCommand(bus, BUS_INTO_KEY, target));
-  return { ...f, ids, into };
+  const routing = routingOf(f);
+  return { ...f, ids, into: (bus: string, target: string) => routing.only(bus, target) };
 }
 
 /** A sound FX that compiles: Input, a Gain, Output. */
@@ -65,56 +65,23 @@ function workingFx(f: ReturnType<typeof makeProject>): string {
 }
 
 describe('the bus asset (#325)', () => {
-  it('is not placeable and starts at full volume, without a sound FX, into the master', () => {
+  it('is not placeable and starts at full volume, without a sound FX', () => {
     expect(isPlaceableType('bus')).toBe(false);
     const f = withBuses('Music');
     const bus = f.project.assets[0]!;
-    expect(buildAsset('bus', 'SFX')).toMatchObject({ type: 'bus', props: { volume: 1, fx: '', into: '' } });
-    expect(schemaForAsset(f.project, bus).map((def) => def.key)).toEqual(['volume', 'fx', 'into']);
+    expect(buildAsset('bus', 'SFX')).toMatchObject({ type: 'bus', props: { volume: 1, fx: '' } });
+    expect(schemaForAsset(f.project, bus).map((def) => def.key)).toEqual(['volume', 'fx']);
     expect(roundTrip(f.project)).toEqual(f.project);
   });
 
-  it('names the master as the empty pick of Into and of the Bus of a sound, an instrument, a pattern and a song', () => {
+  it('leaves where a sound, an instrument, a pattern, a song and a bus go to the routing (#351)', () => {
     const f = withBuses('Music');
-    const into = schemaForAsset(f.project, f.project.assets[0]!).find((def) => def.key === BUS_INTO_KEY);
-    expect(into).toMatchObject({ kind: 'asset', assetTypes: ['bus'], none: 'Master' });
     for (const type of ['sound', 'instrument', 'pattern', 'song'] as const) {
       const command = new CreateAssetCommand(type, type);
       f.stack.execute(command);
-      expect(schemaForAsset(f.project, command.asset).find((def) => def.key === BUS_KEY)).toMatchObject({
-        none: 'Master',
-        assetTypes: ['bus'],
-      });
+      expect(schemaForAsset(f.project, command.asset).map((def) => def.key)).not.toContain('bus');
     }
-  });
-
-  it('offers as Into neither itself nor a bus that already goes into it', () => {
-    const f = withBuses('Master music', 'Music', 'Drums', 'SFX');
-    const [top, music, drums, sfx] = f.ids as [string, string, string, string];
-    f.into(music, top);
-    f.into(drums, music);
-    const rows = schemaForAsset(
-      f.project,
-      f.project.assets.find((a) => a.id === top)!,
-    );
-    expect(rows.find((d) => d.key === BUS_INTO_KEY)).toMatchObject({ intoFor: top });
-    expect(busesInto(f.project, top)).toEqual([top, music, drums]);
-    expect(busesInto(f.project, drums)).toEqual([drums]);
-    expect(busesInto(f.project, sfx)).toEqual([sfx]);
-  });
-
-  it('sends a bus that would come round to itself into the master, whatever the file says', () => {
-    const f = withBuses('A', 'B', 'C');
-    const [a, b, c] = f.ids as [string, string, string];
-    f.into(a, b);
-    f.into(b, c);
-    f.into(c, b);
-    // B and C go round each other: both go into the master. A goes into B, which is no loop.
-    expect([busInto(f.project, a), busInto(f.project, b), busInto(f.project, c)]).toEqual([b, '', '']);
-    f.into(a, a);
-    expect(busInto(f.project, a)).toBe('');
-    f.into(a, 'gone');
-    expect(busInto(f.project, a)).toBe('');
+    expect(schemaForAsset(f.project, f.project.assets[0]!).map((def) => def.key)).not.toContain('into');
   });
 });
 
@@ -167,15 +134,19 @@ describe('the mix (#325)', () => {
     expect(sameMix(before, mixOf(f.project))).toBe(false);
   });
 
-  it('plays on the bus a node picks, else the one its asset names, else the master', () => {
+  it('plays on the bus a node picks, else the one the routing sends its asset to, else the master', () => {
     const f = withBuses('Music', 'SFX');
     const [music, sfx] = f.ids as [string, string];
-    expect(playedBus(f.project, '', { bus: music })).toBe(`mix:${music}`);
-    expect(playedBus(f.project, sfx, { bus: music })).toBe(`mix:${sfx}`);
-    expect(playedBus(f.project, MASTER_BUS, { bus: music })).toBe(MASTER_MIX);
-    expect(playedBus(f.project, '', {})).toBe(MASTER_MIX);
-    // A bus that was deleted leaves it on the master.
-    expect(playedBus(f.project, '', { bus: 'gone' })).toBe(MASTER_MIX);
+    const sound = new CreateSoundCommand('Jump', FILE);
+    f.stack.execute(sound);
+    const id = sound.asset.id;
+    expect(playedBus(f.project, '', id)).toBe(MASTER_MIX);
+    f.into(id, music);
+    expect(playedBus(f.project, '', id)).toBe(`mix:${music}`);
+    expect(playedBus(f.project, sfx, id)).toBe(`mix:${sfx}`);
+    expect(playedBus(f.project, MASTER_BUS, id)).toBe(MASTER_MIX);
+    // A pick of a bus that was deleted leaves it on the master.
+    expect(playedBus(f.project, 'gone', id)).toBe(MASTER_MIX);
   });
 
   it('reaches the master for an empty pick, and no bus for one that is not there', () => {
@@ -219,13 +190,13 @@ function runOnStart(type: string, params: Record<string, string | number | boole
 }
 
 describe('buses in a running game (#325)', () => {
-  it('plays a sound on the bus its asset names, or on the one Play sound picks', () => {
+  it('plays a sound on the bus the routing sends it to, or on the one Play sound picks', () => {
     const f = makeSpriteScene();
     const bus = new CreateAssetCommand('bus', 'SFX');
     const sound = new CreateSoundCommand('Jump', FILE);
     f.stack.execute(bus);
     f.stack.execute(sound);
-    f.stack.execute(new SetAssetPropertyCommand(sound.asset.id, BUS_KEY, bus.asset.id));
+    routingOf(f).only(sound.asset.id, bus.asset.id);
     runOnStart('PlaySound', { sound: sound.asset.id, volume: 1 }, f);
     const asset = busSink();
     startWorld(f, { behaviors: true, audio: asset }).frame();

tests/core/embedded.test.ts

@@ -71,8 +71,7 @@ describe('an embedded asset (#355)', () => {
   it('hides the rows that do nothing in a song, only while embedded', () => {
     const { f, takeId, blipId } = setup();
     const take = findAsset(f.project, takeId)!;
-    expect(['loop', 'bus', 'reverse', 'fx'].map((k) => isRowHiddenWhenEmbedded(take, k))).toEqual([
-      true,
+    expect(['loop', 'reverse', 'fx'].map((k) => isRowHiddenWhenEmbedded(take, k))).toEqual([
       true,
       false,
       false,
@@ -308,18 +307,11 @@ describe('a pattern made in a song (#355)', () => {
     ]);
   });
 
-  it('hides only its bus, not its clock, length, instrument or sound FX (#363)', () => {
+  it('hides none of its rows: not its clock, length, instrument or sound FX (#363)', () => {
     const { make } = withPatterns();
     const own = make();
-    const keys = ['bus', 'tempo', 'sign', 'bars', 'instrument', 'fx'];
-    expect(keys.map((k) => isRowHiddenWhenEmbedded(own, k))).toEqual([
-      true,
-      false,
-      false,
-      false,
-      false,
-      false,
-    ]);
+    const keys = ['tempo', 'sign', 'bars', 'instrument', 'fx'];
+    expect(keys.map((k) => isRowHiddenWhenEmbedded(own, k))).toEqual([false, false, false, false, false]);
   });
 
   it('plays the instrument of the pattern on its track that starts last before it, else the first after', () => {

tests/core/graph.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest';
-import { isSongRoutingDef } from '../../src/core/music/routingNodes';
+import { isMasterRoutingDef, isSongRoutingDef } from '../../src/core/music/routingNodes';
 import { requireNodeDef } from '../../src/core/commands/require';
 import { CommandError } from '../../src/core/commands/Command';
 import {
@@ -82,9 +82,11 @@ describe('node registry', () => {
       else if (def.category === 'state') expect(def.run).toBeUndefined();
       // A shader node is compiled to GLSL, a particle node to a function, a sound FX node to a
       // stage of a voice, an instrument's own node to part of a note and a node of a song's routing
-      // to its buses (#350): none is ever run.
+      // (#350) or of the master routing (#351) to buses: none is ever run.
       else if (def.category === 'shader' || def.category === 'particles' || def.category === 'sound')
-        expect('emit' in def || 'instrument' in def || isSongRoutingDef(def)).toBe(true);
+        expect('emit' in def || 'instrument' in def || isSongRoutingDef(def) || isMasterRoutingDef(def)).toBe(
+          true,
+        );
       // The end of a block runs as part of the node that opens it (`Find` … `Match`).
       else if (defs.some((d) => d.opens?.type === def.type)) expect(def.run).toBeUndefined();
       // Everything else does one of the two: a step (`run`), or an answer whenever asked (`read`).

tests/core/holders.test.ts

@@ -155,6 +155,7 @@ describe('CommandStack', () => {
       renderLayers: ['Default'],
       masterVolume: 1,
       masterFx: '',
+      routing: { nodes: [], edges: [] },
       symbolScale: 1,
       playFrom: 'start' as const,
       whilePlaying: 'live' as const,

tests/core/master-routing.test.ts

@@ -0,0 +1,265 @@
+/**
+ * The master routing (#351): a node per sound, instrument, pattern, song and bus and the master,
+ * following the assets through every edit and its undo, and the mix the links make.
+ */
+import { describe, expect, it } from 'vitest';
+import {
+  CreateAssetCommand,
+  CreateSoundCommand,
+  DeleteAssetCommand,
+  RenameAssetCommand,
+} from '../../src/core/commands/assetCommands';
+import type { Command } from '../../src/core/commands/Command';
+import { ConnectCommand, DisconnectCommand } from '../../src/core/commands/graphCommands';
+import { KeepRoutingCommand } from '../../src/core/commands/routingCommands';
+import { SetSendCommand } from '../../src/core/commands/songCommands';
+import type { Graph } from '../../src/core/graph/Graph';
+import { ROUTING_ID } from '../../src/core/model/Project';
+import { MASTER_MIX, mixBusName, mixOf, playedRoute, routeOf, sameMix } from '../../src/core/music/mixer';
+import { heldRouting, masterRoutingProblems, settleRouting } from '../../src/core/music/projectRouting';
+import { ROUTED_ASSET, ROUTED_MASTER } from '../../src/core/music/routingNodes';
+import { MASTER_BUS } from '../../src/core/properties/buses';
+import { makeProject, roundTrip } from '../helpers';
+
+const FILE = `${'b2'.repeat(32)}.wav`;
+
+/** A project edited as the editor edits it: every command keeps the routing in step (#351). */
+function edited() {
+  const f = makeProject();
+  const run = (command: Command) => f.stack.execute(new KeepRoutingCommand(command));
+  const create = (type: 'bus' | 'instrument' | 'pattern' | 'song' | 'scene', name: string) => {
+    const command = new CreateAssetCommand(type, name);
+    run(command);
+    return command.asset.id;
+  };
+  const sound = (name: string) => {
+    const command = new CreateSoundCommand(name, FILE);
+    run(command);
+    return command.asset.id;
+  };
+  const link = (from: string, to: string) => {
+    const command = new ConnectCommand(ROUTING_ID, { node: from, port: 'out' }, { node: to, port: 'in' });
+    run(command);
+    return command.edge.id;
+  };
+  const linksOf = (id: string) =>
+    f.project.routing.edges.filter((e) => e.from.node === id).map((e) => e.to.node);
+  return { ...f, run, create, sound, link, linksOf };
+}
+
+const edge = (from: string, to: string, extra: object = {}) => ({
+  id: `${from}>${to}`,
+  from: { node: from, port: 'out' },
+  to: { node: to, port: 'in' },
+  ...extra,
+});
+
+describe('the nodes of the master routing (#351)', () => {
+  it('come with each sound, instrument, pattern, song and bus, linked to the master', () => {
+    const f = edited();
+    const ids = [f.sound('Kick'), f.create('instrument', 'Lead'), f.create('pattern', 'Riff')];
+    ids.push(f.create('song', 'Theme'), f.create('bus', 'Reverb'), f.sound('Snare'));
+    f.create('scene', 'Level');
+    const nodes = f.project.routing.nodes;
+    expect(nodes.map((n) => n.id).sort()).toEqual([...ids, MASTER_BUS].sort());
+    expect(nodes.find((n) => n.id === MASTER_BUS)?.type).toBe(ROUTED_MASTER);
+    for (const id of ids) expect(f.linksOf(id)).toEqual([MASTER_BUS]);
+    const at = (id: string) => nodes.find((n) => n.id === id)!;
+    expect(at(ids[0]!).type).toBe(ROUTED_ASSET);
+    expect(at(ids[0]!).params).toEqual({ name: 'Kick', kind: 'sound' });
+    // What plays below each other in the first column, the buses in the second, the master right of
+    // them a row above all of it: no link into it runs behind a bus.
+    expect(ids.map((id) => [at(id).x, at(id).y])).toEqual([
+      [0, 0],
+      [0, 80],
+      [0, 160],
+      [0, 240],
+      [320, 0],
+      [0, 320],
+    ]);
+    expect([at(MASTER_BUS).x, at(MASTER_BUS).y]).toEqual([640, -80]);
+  });
+
+  it('come in by type as a project from before the routing is opened', () => {
+    const f = makeProject();
+    for (const command of [
+      new CreateAssetCommand('bus', 'Reverb'),
+      new CreateAssetCommand('song', 'Theme'),
+      new CreateSoundCommand('Kick', FILE),
+      new CreateAssetCommand('instrument', 'Lead'),
+    ])
+      f.stack.execute(command);
+    settleRouting(f.project);
+    const shown = f.project.routing.nodes.map((n) => [n.params.name ?? 'Master', n.x, n.y]);
+    expect(shown).toEqual([
+      ['Kick', 0, 0],
+      ['Lead', 0, 80],
+      ['Theme', 0, 160],
+      ['Reverb', 320, 0],
+      ['Master', 640, -80],
+    ]);
+  });
+
+  it('follow a rename, and go with their asset and its links, all of it back on undo', () => {
+    const f = edited();
+    const kick = f.sound('Kick');
+    const reverb = f.create('bus', 'Reverb');
+    const onMaster = f.project.routing.edges.find((e) => e.from.node === kick)!;
+    f.link(kick, reverb);
+    f.run(new DisconnectCommand(ROUTING_ID, onMaster.id));
+    expect(f.linksOf(kick)).toEqual([reverb]);
+    f.run(new RenameAssetCommand(kick, 'Big kick'));
+    expect(f.project.routing.nodes.find((n) => n.id === kick)?.params.name).toBe('Big kick');
+    f.stack.undo();
+    expect(f.project.routing.nodes.find((n) => n.id === kick)?.params.name).toBe('Kick');
+
+    const before = JSON.stringify(f.project.routing);
+    f.run(new DeleteAssetCommand(reverb));
+    expect(f.project.routing.nodes.some((n) => n.id === reverb)).toBe(false);
+    // The kick went only into the bus, and goes to the master now: deleting a bus silences nothing.
+    expect(f.linksOf(kick)).toEqual([MASTER_BUS]);
+    f.stack.undo();
+    expect(JSON.stringify(f.project.routing)).toBe(before);
+    f.stack.redo();
+    expect(f.project.routing.nodes.some((n) => n.id === reverb)).toBe(false);
+    expect(f.linksOf(kick)).toEqual([MASTER_BUS]);
+  });
+
+  it('leave a node without a link alone when a bus goes that it was not sent to', () => {
+    const f = edited();
+    const kick = f.sound('Kick');
+    const reverb = f.create('bus', 'Reverb');
+    const send = f.project.routing.edges.find((e) => e.from.node === kick)!;
+    f.stack.execute(
+      new KeepRoutingCommand({
+        label: 'Unlink',
+        execute: (p) => void p.routing.edges.splice(p.routing.edges.indexOf(send), 1),
+        undo: () => {},
+      }),
+    );
+    f.run(new DeleteAssetCommand(reverb));
+    expect(f.linksOf(kick)).toEqual([]);
+    expect(masterRoutingProblems(f.project.routing)[kick]).toMatch(/^Goes nowhere/);
+  });
+
+  it('are not added as a project is read, and a settled routing reads back as it was', () => {
+    const f = makeProject();
+    f.stack.execute(new CreateSoundCommand('Kick', FILE));
+    expect(roundTrip(f.project).routing).toEqual({ nodes: [], edges: [] });
+    const g = edited();
+    g.link(g.sound('Kick'), g.create('bus', 'Reverb'));
+    g.create('pattern', 'Riff');
+    expect(roundTrip(g.project)).toEqual(g.project);
+  });
+
+  it('keep no link that would loop, say again what another says, or go into what is no bus', () => {
+    const assets = [
+      { id: 'a', type: 'bus', name: 'A', props: {} },
+      { id: 'b', type: 'bus', name: 'B', props: {} },
+      { id: 's', type: 'sound', name: 'S', props: {} },
+      { id: 'p', type: 'pattern', name: 'P', props: {} },
+    ] as never[];
+    const node = (id: string, kind: string) => ({
+      id,
+      type: ROUTED_ASSET,
+      x: 0,
+      y: 0,
+      params: { name: id, kind },
+    });
+    const graph: Graph = {
+      nodes: [node('a', 'bus'), node('b', 'bus'), node('s', 'sound'), node('p', 'pattern')],
+      edges: [
+        edge('a', 'b'),
+        edge('b', 'a'),
+        edge('s', 'a', { send: { volume: -6, tap: 'preFx' } }),
+        { ...edge('s', 'a'), id: 'again' },
+        edge('p', 's'),
+        edge('b', MASTER_BUS, { send: { volume: 3, tap: 'preFx' } }),
+      ],
+    };
+    const held = heldRouting(graph, assets, false);
+    expect(held.edges.map((e) => e.id)).toEqual(['a>b', 's>a', 'b>#master', expect.any(String)]);
+    // A sound sends after its volume and FX; a bus may tap before them.
+    expect(held.edges.find((e) => e.id === 's>a')?.send).toEqual({ volume: -6, tap: 'post' });
+    expect(held.edges.find((e) => e.id === 'b>#master')?.send).toEqual({ volume: 3, tap: 'preFx' });
+    // The pattern's one link went into a sound: it goes to the master instead.
+    expect(held.edges.at(-1)).toMatchObject({ from: { node: 'p' }, to: { node: MASTER_BUS } });
+  });
+
+  it('take a send of a sound only after its volume, and of a bus from where it is asked', () => {
+    const f = edited();
+    const kick = f.sound('Kick');
+    const reverb = f.create('bus', 'Reverb');
+    const toBus = f.link(kick, reverb);
+    const out = f.project.routing.edges.find((e) => e.from.node === reverb)!.id;
+    f.run(new SetSendCommand(ROUTING_ID, toBus, { volume: -12, tap: 'preFx' }));
+    f.run(new SetSendCommand(ROUTING_ID, out, { volume: 0, tap: 'postFx' }));
+    const sendOf = (id: string) => f.project.routing.edges.find((e) => e.id === id)?.send;
+    expect([sendOf(toBus), sendOf(out)]).toEqual([
+      { volume: -12, tap: 'post' },
+      { volume: 0, tap: 'postFx' },
+    ]);
+  });
+});
+
+describe('the mix of the master routing (#351)', () => {
+  it('sends what has no node, or one link at 0 dB, straight into that bus', () => {
+    const f = makeProject();
+    const sound = new CreateSoundCommand('Kick', FILE);
+    f.stack.execute(sound);
+    expect(routeOf(f.project, sound.asset.id)).toBe(MASTER_MIX);
+    const g = edited();
+    const kick = g.sound('Kick');
+    const reverb = g.create('bus', 'Reverb');
+    expect(routeOf(g.project, kick)).toBe(MASTER_MIX);
+    g.link(kick, reverb);
+    g.run({
+      label: 'Off the master',
+      execute: (p) =>
+        void (p.routing.edges = p.routing.edges.filter(
+          (e) => !(e.from.node === kick && e.to.node === MASTER_BUS),
+        )),
+      undo: () => {},
+    });
+    expect(routeOf(g.project, kick)).toBe(mixBusName(reverb));
+  });
+
+  it('gives a sound with more than that a bus of its own with its sends, and plays a song along them', () => {
+    const f = edited();
+    const kick = f.sound('Kick');
+    const song = f.create('song', 'Theme');
+    const reverb = f.create('bus', 'Reverb');
+    const send = f.link(kick, reverb);
+    f.run(new SetSendCommand(ROUTING_ID, send, { volume: -6, tap: 'post' }));
+    const before = mixOf(f.project);
+    const own = before.find((bus) => bus.name === mixBusName(kick));
+    expect(own).toMatchObject({ volume: 1, fx: null });
+    expect(own?.sends?.map((s) => [s.to, s.tap, Math.round(s.gain * 1000) / 1000])).toEqual([
+      [MASTER_MIX, 'post', 1],
+      [mixBusName(reverb), 'post', 0.501],
+    ]);
+    expect(before.find((bus) => bus.name === mixBusName(reverb))).toMatchObject({ into: MASTER_MIX });
+    expect(before.some((bus) => bus.name === mixBusName(song))).toBe(false);
+    f.run(new SetSendCommand(ROUTING_ID, send, { volume: -3, tap: 'post' }));
+    expect(sameMix(before, mixOf(f.project))).toBe(false);
+
+    const toReverb = f.link(song, reverb);
+    f.run(new SetSendCommand(ROUTING_ID, toReverb, { volume: 0, tap: 'preFx' }));
+    const route = playedRoute(f.project, '', song);
+    expect(typeof route !== 'string' && route.map((s) => [s.to, s.tap])).toEqual([
+      [MASTER_MIX, 'post'],
+      [mixBusName(reverb), 'preFx'],
+    ]);
+    // A bus the node picks takes it there alone.
+    expect(playedRoute(f.project, reverb, song)).toBe(mixBusName(reverb));
+    expect(playedRoute(f.project, MASTER_BUS, song)).toBe(MASTER_MIX);
+  });
+
+  it('plays an asset with no link at all on nothing', () => {
+    const f = edited();
+    const kick = f.sound('Kick');
+    f.run({ label: 'Unlink', execute: (p) => void (p.routing.edges = []), undo: () => {} });
+    expect(routeOf(f.project, kick)).toEqual([]);
+    expect(mixOf(f.project).find((bus) => bus.name === mixBusName(kick))?.sends).toEqual([]);
+  });
+});

tests/core/pattern.test.ts

@@ -56,7 +56,6 @@ describe('pattern asset (#333)', () => {
       'sign',
       'tempo',
       'fx',
-      'bus',
     ]);
   });
 

tests/core/song.test.ts

@@ -71,13 +71,7 @@ describe('the song asset (#334)', () => {
     const f = makeSong(1);
     expect(f.song().tracks.map((t) => t.name)).toEqual(['Track 1']);
     expect(f.song().items).toEqual([]);
-    expect(schemaForAsset(f.project, f.song()).map((d) => d.key)).toEqual([
-      'tempo',
-      'sign',
-      'grid',
-      'fx',
-      'bus',
-    ]);
+    expect(schemaForAsset(f.project, f.song()).map((d) => d.key)).toEqual(['tempo', 'sign', 'grid', 'fx']);
     expect(songGrid(f.song().props)).toBe(BAR);
     f.stack.execute(new SetAssetPropertyCommand(f.song().id, 'grid', '1/8T'));
     expect(songGrid(f.song().props)).toBe(160);

tests/core/sounds.test.ts

@@ -40,7 +40,6 @@ import {
   VOLUME_KEY,
   volumeOf,
 } from '../../src/core/properties/sounds';
-import { BUS_KEY } from '../../src/core/properties/buses';
 import { deserializeProject } from '../../src/core/store/serialize';
 import type { AudioSink } from '../../src/runtime/systems/Audio';
 import {
@@ -131,7 +130,7 @@ describe('the sound asset', () => {
     expect(volumeOf(asset.props)).toBe(1);
     expect(loopsOf(asset.props)).toBe(false);
     // The cut belongs to a clip of the sound (#357), the sound is the whole file.
-    expect(schemaFor('sound').map((def) => def.key)).toEqual([VOLUME_KEY, LOOP_KEY, 'fx', BUS_KEY]);
+    expect(schemaFor('sound').map((def) => def.key)).toEqual([VOLUME_KEY, LOOP_KEY, 'fx']);
     expect(CLIP_ROWS.map((def) => def.key)).toEqual([
       START_KEY,
       END_KEY,

tests/editor/edge-selection.test.ts

@@ -189,6 +189,7 @@ describe('a selection of links', () => {
       type: 'number',
       name: '',
       send: null,
+      tapped: false,
     });
     expect(describeEdge(f.state.project, f.behaviorId, 'gone')).toBeNull();
     expect(edgeSignature(f.state.project, f.behaviorId, f.first, [f.first, f.second])).toBe('many:2');

tests/helpers.ts

@@ -1,6 +1,6 @@
 import { CreateAssetCommand } from '../src/core/commands/assetCommands';
 import { CommandStack } from '../src/core/commands/CommandStack';
-import { AddNodeCommand, ConnectCommand } from '../src/core/commands/graphCommands';
+import { AddNodeCommand, ConnectCommand, DisconnectCommand } from '../src/core/commands/graphCommands';
 import { AddPortsCommand } from '../src/core/commands/portCommands';
 import { PlaceAssetCommand } from '../src/core/commands/sceneObjectCommands';
 import { requireNodeDef } from '../src/core/commands/require';
@@ -29,7 +29,9 @@ import { findObject } from '../src/core/model/hierarchy';
 import { worldPosition } from '../src/core/properties/transform';
 import { resolvedHolder } from '../src/core/model/instance';
 import type { Position, PropertyBag, Vec2 } from '../src/core/model/Properties';
-import { createEmptyProject, findScene, type Project } from '../src/core/model/Project';
+import { createEmptyProject, findScene, type Project, ROUTING_ID } from '../src/core/model/Project';
+import { settleRouting } from '../src/core/music/projectRouting';
+import { MASTER_BUS } from '../src/core/properties/buses';
 import type { SceneObject } from '../src/core/model/SceneObject';
 import { deserializeProject, serializeProject } from '../src/core/store/serialize';
 import type { AudioSink } from '../src/runtime/systems/Audio';
@@ -65,6 +67,28 @@ export function makeProject(): ProjectFixture {
   return { project, stack: new CommandStack(project) };
 }
 
+/**
+ * The master routing of a fixture (#351), held to its assets before each change: `link` adds a link
+ * from an asset to a bus or the master, `only` makes that its one link.
+ */
+export function routingOf({ project, stack }: ProjectFixture) {
+  const link = (from: string, to = MASTER_BUS) => {
+    settleRouting(project);
+    const command = new ConnectCommand(ROUTING_ID, { node: from, port: 'out' }, { node: to, port: 'in' });
+    stack.execute(command);
+    return command.edge;
+  };
+  return {
+    link,
+    only(from: string, to = MASTER_BUS) {
+      settleRouting(project);
+      for (const edge of project.routing.edges.filter((e) => e.from.node === from))
+        stack.execute(new DisconnectCommand(ROUTING_ID, edge.id));
+      return link(from, to);
+    },
+  };
+}
+
 /** A project with a scene "Level" and a 100×100 sprite (named "Box" unless told otherwise), plus lookups into the scene. */
 export function makeSpriteScene(spriteName = 'Box'): SceneFixture {
   const fixture = makeProject();

tests/viewport/sound-library.test.ts

@@ -2295,6 +2295,50 @@ describe('the master and the buses of the project (#325)', () => {
     expect(levels(library).map((level) => level.name)).toEqual(['mix', 'mix:a']);
   });
 
+  it('sends a bus of the mix along the links of the master routing, and back into one bus (#351)', async () => {
+    const library = new SoundLibrary(false);
+    await play(library);
+    const sends = [
+      { to: 'mix', gain: 1, tap: 'post' as const },
+      { to: 'mix:a', gain: 0.5, tap: 'preFx' as const },
+    ];
+    await library.setMix([mix[0]!, mix[1]!, { ...mix[2]!, sends }]);
+    const b = library.busLevels().find((level) => level.name === 'mix:b');
+    expect(b?.sends?.map(({ to, gain, tap }) => [to, gain, tap])).toEqual([
+      ['mix', 1, 'post'],
+      ['mix:a', 0.5, 'preFx'],
+    ]);
+    expect(b?.into).toBeNull();
+    await library.setMix(mix);
+    expect(levels(library).at(-1)).toEqual({ name: 'mix:b', gain: 0.25, into: 'mix:a' });
+  });
+
+  it('sends the master of a playing along the links of its pattern or song (#351)', async () => {
+    const library = new SoundLibrary(false);
+    await library.setMix(mix);
+    const id = library.playSequence(
+      'song:s',
+      {
+        sequence: { notes: [{ tick: 0, length: 480, velocity: 1, instrument: 'i', note: 60 }] },
+        tempo: 120,
+        length: 1920,
+        loop: null,
+        needs: { layers: [], files: [] },
+        sends: [
+          { to: 'mix', gain: 1, tap: 'post' },
+          { to: 'mix:b', gain: 0.25, tap: 'preFx' },
+        ],
+        strike: () => 0,
+      },
+      '',
+    );
+    const master = library.busLevels().find((level) => level.name === `play:${id}`);
+    expect(master?.sends?.map(({ to, gain, tap }) => [to, gain, tap])).toEqual([
+      ['mix', 1, 'post'],
+      ['mix:b', 0.25, 'preFx'],
+    ]);
+  });
+
   it('holds the volume a game sets over that of the asset until it is reset, gliding there over its time', async () => {
     const library = new SoundLibrary(false);
     await library.setMix(mix);

tools/e2e/34-sound.mjs

@@ -20,7 +20,7 @@ const DRONE_BYTES = 12044;
 
 export async function sound(t) {
   const { check, sleep, json, evaluate, mutate, click, clickText, press, play, stop, shot, showTab } = t;
-  const { select } = t;
+  const { select, drag } = t;
   const assetsOfType = (type) =>
     json(`__gm.state.project.assets.filter((a) => a.type === ${JSON.stringify(type)})
       .map((a) => ({ id: a.id, name: a.name, file: a.file, props: a.props }))`);
@@ -2262,55 +2262,123 @@ export async function sound(t) {
     JSON.stringify({ clips: await clips(), current: await json('__gm.soundTab.current()') }),
   );
 
-  // 34h-3. Buses and the master (#325). "+ → Bus" makes one into the master; its Into never offers
-  //        itself nor a bus that goes into it; the Sound tab plays a sound on its bus, and the
-  //        master's volume is a project setting, one undo step.
+  // 34h-3. Buses and the master (#325), routed in the Master routing tab (#351). "+ → Bus" makes
+  //        one; the tab has a node for it and for the sound, each linked to the master. Links drawn
+  //        there and one deleted send the sound into a bus and that bus into the other, as the Sound
+  //        tab then plays it. A click on a node shows its asset, on the master the master's volume.
   for (let i = 0; i < 2; i++) {
     await clickText('+');
     await pickAssetType(t, 'Bus');
     await sleep(150);
   }
   const [busA, busB] = await assetsOfType('bus');
-  const intoMenu = async () => {
-    await select({ kind: 'asset', assetId: busA.id });
-    const at = await json("__gm.inspectorField('Into', true)");
-    await click(at.x, at.y);
-    const offered = await json('__gm.overlayTexts()');
-    await press('Escape');
-    return offered;
-  };
-  const offeredBefore = await intoMenu();
-  await mutate(`
-    const p = __gm.state.project;
-    p.assets.find((a) => a.id === ${JSON.stringify(busB.id)}).props.into = ${JSON.stringify(busA.id)};`);
-  const offeredAfter = await intoMenu();
+  await t.clickToolbar('menu');
+  await clickText('Master routing');
+  await sleep(300);
+  const routing = () => json('__gm.routing.graph()');
+  const links = (graph) => graph.edges.map((e) => `${e.from.node}>${e.to.node}`);
+  const opened = { shown: await json('__gm.routing.shown()'), graph: await routing() };
+  const labels = await json(
+    `[${JSON.stringify(droneId)}, ${JSON.stringify(busA.id)}, '#master'].map((id) => __gm.routing.label(id))`,
+  );
+  await select({ kind: 'asset', assetId: droneId });
+  const busRow = await json("__gm.inspectorField('Bus', true)");
+  await select({ kind: 'asset', assetId: busA.id });
+  const intoRow = await json("__gm.inspectorField('Into', true)");
   check(
-    '"+ → Bus" makes buses into the master, and Into offers neither the bus itself nor one going into it',
-    [busA, busB].every((bus) => bus.props.volume === 1 && bus.props.fx === '' && bus.props.into === '') &&
-      JSON.stringify(offeredBefore) === JSON.stringify(['Search…', 'Master', `${busB.name} (bus)`]) &&
-      JSON.stringify(offeredAfter) === JSON.stringify(['Search…', 'Master']),
-    JSON.stringify({ busA, busB, offeredBefore, offeredAfter }),
+    'Menu → Master routing has a node per sound and bus and the master, each linked to the master; no Bus or Into rows',
+    opened.shown &&
+      [droneId, busA.id, busB.id, '#master'].every((id) => opened.graph.nodes.some((n) => n.id === id)) &&
+      [droneId, busA.id, busB.id].every((id) => links(opened.graph).includes(`${id}>#master`)) &&
+      JSON.stringify(labels) === JSON.stringify(['drone', busA.name, 'Master']) &&
+      [busA, busB].every((bus) => bus.props.volume === 1 && bus.props.fx === '' && !('into' in bus.props)) &&
+      busRow === null &&
+      intoRow === null,
+    JSON.stringify({ opened, labels, busRow, intoRow, busA, busB }),
   );
 
+  const portOf = (nodeId, key, isOutput) =>
+    json(`__gm.routing.portAt(${JSON.stringify(nodeId)}, ${JSON.stringify(key)}, ${isOutput})`);
+  const link = async (from, to) => {
+    const a = await portOf(from, 'out', true);
+    const b = await portOf(to, 'in', false);
+    await drag(a.x, a.y, b.x, b.y);
+    await sleep(200);
+  };
+  // The link is picked by the model: its line may run behind a node, as lines do.
+  const unlink = async (from, to) => {
+    const edge = (await routing()).edges.find((e) => e.from.node === from && e.to.node === to);
+    await select({ kind: 'edge', assetId: '#routing', edgeId: edge.id, edgeIds: [edge.id] });
+    await press('Delete');
+    await sleep(150);
+  };
+  await link(droneId, busB.id);
+  await link(busB.id, busA.id);
+  await unlink(droneId, '#master');
+  await unlink(busB.id, '#master');
+  await shot('h3-routing');
   await mutate(`
-    const p = __gm.state.project;
-    p.assets.find((a) => a.id === ${JSON.stringify(busA.id)}).props.volume = 0.5;
-    p.assets.find((a) => a.id === ${JSON.stringify(droneId)}).props.bus = ${JSON.stringify(busB.id)};`);
+    __gm.state.project.assets.find((a) => a.id === ${JSON.stringify(busA.id)}).props.volume = 0.5;`);
   await evaluate(`__gm.state.openAsset(${JSON.stringify(droneId)})`);
   const startedBefore = (await stats()).started;
   await click(tabPlay.x, tabPlay.y);
   await waitFor(stats, (s) => s.started > startedBefore, 10);
+  await sleep(300);
   const buses = await json('__gm.sound.buses()');
   const heardOn = (await stats()).last?.bus;
+  const peak = await waitFor(
+    () => json(`__gm.routing.peaks([${JSON.stringify(`mix:${busB.id}`)}])`),
+    (peaks) => Math.max(...(peaks[`mix:${busB.id}`] ?? [0])) > 0.01,
+  );
+  await click(tabPlay.x, tabPlay.y);
   const levelOf = (name) => buses.find((bus) => bus.name === name);
   check(
-    'the Sound tab plays the sound on its bus, into the bus that one names, on into the master',
-    heardOn === `mix:${busB.id}` &&
+    'linked in the routing, the Sound tab plays the sound on its bus, into the bus that one goes to, on into the master',
+    links(await routing())
+      .filter((l) => l.startsWith(droneId) || l.startsWith(busB.id))
+      .join() === `${droneId}>${busB.id},${busB.id}>${busA.id}` &&
+      heardOn === `mix:${busB.id}` &&
       levelOf(`mix:${busB.id}`)?.into === `mix:${busA.id}` &&
       levelOf(`mix:${busA.id}`)?.into === 'mix' &&
       levelOf(`mix:${busA.id}`)?.gain === 0.5 &&
-      levelOf('mix')?.into === null,
-    JSON.stringify({ heardOn, buses }),
+      levelOf('mix')?.into === null &&
+      Math.max(...(peak?.[`mix:${busB.id}`] ?? [0])) > 0.01,
+    JSON.stringify({ links: links(await routing()), heardOn, buses, peak }),
+  );
+
+  await t.clickToolbar('menu');
+  await clickText('Master routing');
+  await sleep(200);
+  let at = await json(`__gm.routing.nodeAt(${JSON.stringify(busA.id)})`);
+  await click(at.x, at.y);
+  await sleep(200);
+  const busShown = await json("__gm.inspectorField('Volume', true)");
+  at = await json("__gm.routing.nodeAt('#master')");
+  await click(at.x, at.y);
+  await sleep(200);
+  await shot('h3-master');
+  const masterField = await json("__gm.inspectorField('Volume', true)");
+  await click(masterField.x, masterField.y);
+  await press('a', { ctrl: true });
+  await t.typeText('0.6');
+  await press('Enter');
+  await sleep(150);
+  const masterSet = await json('__gm.state.project.masterVolume');
+  await t.clickToolbar('undo');
+  await sleep(150);
+  const masterShown = { set: masterSet, undone: await json('__gm.state.project.masterVolume') };
+  at = await json(`__gm.routing.nodeAt(${JSON.stringify(droneId)})`);
+  await click(at.x, at.y);
+  await click(at.x, at.y);
+  await sleep(300);
+  check(
+    'a click on a node shows its asset in the inspector, on the master the master volume, a double click opens the sound',
+    busShown !== null &&
+      masterShown.set === 0.6 &&
+      masterShown.undone === 1 &&
+      (await json('__gm.soundTab.current()')) === droneId &&
+      (await json('__gm.routing.shown()')) === false,
+    JSON.stringify({ busShown, masterShown, current: await json('__gm.soundTab.current()') }),
   );
 
   await t.clickToolbar('menu');
@@ -2337,10 +2405,11 @@ export async function sound(t) {
     mastered.project === 0.6 && mastered.heard === 0.6 && undone.project === 1 && undone.heard === 1,
     JSON.stringify({ masterAt, mastered, undone }),
   );
+  // The routing starts again from the assets with the next edit: everything on the master.
   await mutate(`
     const p = __gm.state.project;
-    p.assets.find((a) => a.id === ${JSON.stringify(droneId)}).props.bus = '';
-    p.assets = p.assets.filter((a) => a.type !== 'bus');`);
+    p.assets = p.assets.filter((a) => a.type !== 'bus');
+    p.routing = { nodes: [], edges: [] };`);
 
   // 34i. The step takes back everything it made, so the steps after it see the fixture again.
   await mutate(`