Snap to the grid from the start in every graph tab (#391)

Laying out a graph by hand mostly means lining nodes up, so the
magnet was switched on in nearly every session. Every graph tab now
starts with it lit: Behavior, State machine, Shader, Particles,
Sound FX, Instrument, the song's Routing and the Routing tab.

- SnapToggle takes the state it starts in and lights its button to
  match. GRAPH_SNAPS_AT_FIRST sets it for the toggles and for
  GraphCanvas alike, so button and canvas cannot disagree.
- Curve and Vector Art are no graphs and still start without it.
- New hook __gm.graphSnapping(on?) reads every graph tab's magnet,
  or "mixed" where button and canvas differ, and switches them all.
- The e2e harness reads the magnets after each navigate() and then
  switches them off, as it already sets the zoom transition to 0.
  Most checks drag a node to an exact spot. e2e 45 does the same
  itself, because the editor comes up there through the sign-in.
- e2e 06 checks that all eight graph tabs started with the magnet on.
  The checks in 06, 26 and 65 that read it off now say they read
  what the harness left.

Tests:
- Unit snap-toggle: 4 tests, 1 new (lit at first, nothing asked of
  the target before a click).
- e2e 06 (melektaus-atx): 150 checks, 1 new. e2e 34: 134 checks.
- Gate (melektaus-atx, together with #390): 287 files, 4397 tests.
- Pictures looked at: none, the state comes from the hook.

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

src/editor/debug/uiHooks.ts

@@ -373,6 +373,32 @@ export function uiHooks({ app, state, editor }: HookContext) {
       if (ms !== undefined) keepGeneralSettings({ zoomTransitionMs: ms });
       return generalSettings().zoomTransitionMs;
     },
+    /**
+     * Whether each graph tab's magnet is on (#391); with `on` they are all switched first. The
+     * harness reads them on every load and then switches them off, so a drag lands where it is let go.
+     */
+    graphSnapping: (on?: boolean) => {
+      const tabs = {
+        logic: [editor.graphEditor.snap, editor.graphEditor.canvas],
+        stateMachine: [editor.stateMachineEditor.snap, editor.stateMachineEditor.canvas],
+        shader: [editor.shaderEditor.snap, editor.shaderEditor.canvas],
+        particles: [editor.particlesEditor.snap, editor.particlesEditor.canvas],
+        soundFx: [editor.soundFxEditor.snap, editor.soundFxEditor.canvas],
+        instrument: [editor.instrumentEditor.snap, editor.instrumentEditor.canvas],
+        song: [editor.songEditor.snap, editor.songEditor.routing],
+        routing: [editor.routingEditor.snap, editor.routingEditor.canvas],
+      } as const;
+      if (on !== undefined) for (const [snap] of Object.values(tabs)) snap.set(on);
+      // The magnet lit and the canvas snapping, or "mixed" where the two disagree.
+      return Object.fromEntries(
+        Object.entries(tabs).map(([tab, [snap, canvas]]) => [
+          tab,
+          snap.button.toggled === canvas.snapEnabled && snap.snapping === canvas.snapEnabled
+            ? canvas.snapEnabled
+            : 'mixed',
+        ]),
+      );
+    },
     /** The "Open project" dialog (#183): the projects it lists and the row picked. */
     projectPicker: () => editor.projectPickerDialog()?.info() ?? null,
     /** The "Snapshots" dialog (#231): its rows, newest first, the row picked and its name field. */

src/editor/graph/GraphCanvas.ts

@@ -82,6 +82,7 @@ import { type PaletteEntry, paletteEntries } from './paletteEntries';
 import { NODE_WIDTH, NodeView, TITLE_HEIGHT } from './NodeView';
 import type { NodeFace } from './nodeFace';
 import { drawGraphGrid, FIT_MARGIN, inView, ZOOM_LIMITS, zoomedAbout } from './graphView';
+import { GRAPH_SNAPS_AT_FIRST } from './SnapToggle';
 import { GraphWiring } from './wiring';
 
 /** One running instance's answer for a machine: which state it holds, and whose instance it is. */
@@ -136,7 +137,7 @@ export class GraphCanvas extends Widget {
     draw: () => this.applyView(),
   });
   private panning: { startX: number; startY: number; panX: number; panY: number } | null = null;
-  private snapping = false;
+  private snapping = GRAPH_SNAPS_AT_FIRST;
   private readonly wiring: GraphWiring;
   private readonly drags: GraphDrags;
   /** A rubber-band selection in progress, in graph coordinates. */

src/editor/graph/GraphEditor.ts

@@ -4,14 +4,14 @@ import { AssetTabEditor } from '../AssetTabEditor';
 import type { EditorState } from '../state';
 import { Breadcrumb } from './Breadcrumb';
 import { GraphCanvas } from './GraphCanvas';
-import { SnapToggle } from './SnapToggle';
+import { GRAPH_SNAPS_AT_FIRST, SnapToggle } from './SnapToggle';
 import { backTo, descend, follow, type Trail } from './trail';
 
 /** Room kept for the "N nodes · M links" readout, wide enough for a three-digit graph. */
 const INFO_WIDTH = 150;
 
 export class GraphEditor extends AssetTabEditor<BehaviorAsset, GraphCanvas> {
-  readonly snap = new SnapToggle(() => this.canvas);
+  readonly snap = new SnapToggle(() => this.canvas, GRAPH_SNAPS_AT_FIRST);
   readonly breadcrumb = new Breadcrumb();
   private trail: Trail = [];
   /** A call followed into another behavior: the tab goes on to that document (#171). */

src/editor/graph/SnapToggle.ts

@@ -6,12 +6,20 @@ export interface Snappable {
   setSnapping(on: boolean): void;
 }
 
-/** The magnet every tab that snaps carries in its header (#194): an icon toggle, off at first. */
+/** A graph, any of them, snaps from the start (#391); a curve and a vector art wait for the magnet. */
+export const GRAPH_SNAPS_AT_FIRST = true;
+
+/**
+ * The magnet every tab that snaps carries in its header (#194): an icon toggle, lit at first where
+ * its target starts snapping, as every graph does (#391).
+ */
 export class SnapToggle {
   readonly button: Button;
-  private on = false;
 
-  constructor(private readonly target: () => Snappable) {
+  constructor(
+    private readonly target: () => Snappable,
+    private on = false,
+  ) {
     this.button = new Button('', {
       width: Theme.controlHeight,
       icon: HEADER_ICON_SVG.snap,
@@ -19,6 +27,11 @@ export class SnapToggle {
       tooltip: 'Snap to the grid',
       onClick: () => this.set(!this.on),
     });
+    this.button.setToggled(on);
+  }
+
+  get snapping(): boolean {
+    return this.on;
   }
 
   get widgets(): readonly Button[] {

src/editor/instrument/InstrumentEditor.ts

@@ -28,7 +28,7 @@ import { Button, Dropdown, Label, Menu, VStack, type Widget } from '../../ui';
 import { soundLibrary } from '../../viewport/SoundLibrary';
 import { AssetTabEditor } from '../AssetTabEditor';
 import { GraphCanvas } from '../graph/GraphCanvas';
-import { SnapToggle } from '../graph/SnapToggle';
+import { GRAPH_SNAPS_AT_FIRST, SnapToggle } from '../graph/SnapToggle';
 import { TOOLBAR_ICON_SVG } from '../panels/toolbarIcons';
 import { PreviewParams } from '../soundfx/PreviewParams';
 import type { EditorState } from '../state';
@@ -51,7 +51,7 @@ const AUDITION_DELAY_MS = 150;
  * them at once, a preset is heard on the keys.
  */
 export class InstrumentEditor extends AssetTabEditor<InstrumentAsset, GraphCanvas> {
-  readonly snap = new SnapToggle(() => this.canvas);
+  readonly snap = new SnapToggle(() => this.canvas, GRAPH_SNAPS_AT_FIRST);
   /** Public for the check scripts. */
   readonly keyboard = new PianoKeyboard();
   readonly stopButton: Button;

src/editor/particles/ParticlesEditor.ts

@@ -6,7 +6,7 @@ import { Button, HStack, Label, Slider, Spacer, type Splitter, Theme, VStack, ty
 import { AssetTabEditor } from '../AssetTabEditor';
 import { GraphCanvas } from '../graph/GraphCanvas';
 import { PreviewSplit } from '../PreviewSplit';
-import { SnapToggle } from '../graph/SnapToggle';
+import { GRAPH_SNAPS_AT_FIRST, SnapToggle } from '../graph/SnapToggle';
 import type { EditorState } from '../state';
 import { ParticlePreview } from './ParticlePreview';
 
@@ -25,7 +25,7 @@ const HOLD_WIDTH = 52;
  */
 export class ParticlesEditor extends AssetTabEditor<ParticlesAsset, GraphCanvas> {
   readonly preview: ParticlePreview;
-  readonly snap = new SnapToggle(() => this.canvas);
+  readonly snap = new SnapToggle(() => this.canvas, GRAPH_SNAPS_AT_FIRST);
   /** Public for the check scripts: the one control they have to hit rather than read. */
   readonly slider = new Slider(0, 0, MIN_SPAN, 120);
   private readonly holdButton = new Button('Hold', {

src/editor/routing/RoutingEditor.ts

@@ -2,7 +2,7 @@ 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 { GRAPH_SNAPS_AT_FIRST, SnapToggle } from '../graph/SnapToggle';
 import type { EditorState } from '../state';
 import { TabHeader } from '../TabHeader';
 
@@ -22,7 +22,7 @@ export class RoutingEditor extends VStack {
   constructor(private readonly state: EditorState) {
     super();
     this.canvas = new GraphCanvas(state, 'routing');
-    this.snap = new SnapToggle(() => this.canvas);
+    this.snap = new SnapToggle(() => this.canvas, GRAPH_SNAPS_AT_FIRST);
     this.fitButton = new Button('Fit', { onClick: () => this.canvas.fit() });
     this.info.minWidth = INFO_WIDTH;
     const header = new TabHeader();

src/editor/shader/ShaderEditor.ts

@@ -19,7 +19,7 @@ import {
 import { shaderLibrary } from '../../viewport/ShaderLibrary';
 import { AssetTabEditor } from '../AssetTabEditor';
 import { GraphCanvas } from '../graph/GraphCanvas';
-import { SnapToggle } from '../graph/SnapToggle';
+import { GRAPH_SNAPS_AT_FIRST, SnapToggle } from '../graph/SnapToggle';
 import { PreviewSplit } from '../PreviewSplit';
 import type { EditorState } from '../state';
 import {
@@ -50,7 +50,7 @@ const FUNCTION_SUBJECT = 'A function shows in the shaders calling it';
  * frame – so the shader is judged on the image it is meant for; before that, a built-in test image.
  */
 export class ShaderEditor extends AssetTabEditor<ShaderTabAsset, GraphCanvas> {
-  readonly snap = new SnapToggle(() => this.canvas);
+  readonly snap = new SnapToggle(() => this.canvas, GRAPH_SNAPS_AT_FIRST);
   readonly preview: ShaderPreview;
   /** Assigned by `body`; public for the check scripts, which drag it. */
   splitter!: Splitter;

src/editor/song/SongEditor.ts

@@ -40,7 +40,7 @@ import {
 import { activateAsset } from '../actions';
 import { AssetTabEditor } from '../AssetTabEditor';
 import { GraphCanvas } from '../graph/GraphCanvas';
-import { SnapToggle } from '../graph/SnapToggle';
+import { GRAPH_SNAPS_AT_FIRST, SnapToggle } from '../graph/SnapToggle';
 import { BakeButton } from '../music/BakeButton';
 import { clockText } from '../music/timeView';
 import { claimTransport, releaseTransport } from '../music/transport';
@@ -93,7 +93,7 @@ export class SongEditor extends AssetTabEditor<SongAsset, SongTimeline> {
   readonly routingButton: Button;
   readonly bakeButton: BakeButton;
   readonly routing: GraphCanvas;
-  readonly snap = new SnapToggle(() => this.routing);
+  readonly snap = new SnapToggle(() => this.routing, GRAPH_SNAPS_AT_FIRST);
   private shown: SongView = 'timeline';
   private readonly pane = new VStack();
   /** Heard through the sound FX (#352), then straight into the master: a preview leaves the routing out (#368). */

src/editor/soundfx/SoundFxEditor.ts

@@ -10,7 +10,7 @@ import { soundLibrary } from '../../viewport/SoundLibrary';
 import { MASTER_MIX } from '../../core/music/mixer';
 import { AssetTabEditor } from '../AssetTabEditor';
 import { GraphCanvas } from '../graph/GraphCanvas';
-import { SnapToggle } from '../graph/SnapToggle';
+import { GRAPH_SNAPS_AT_FIRST, SnapToggle } from '../graph/SnapToggle';
 import { TOOLBAR_ICON_SVG } from '../panels/toolbarIcons';
 import type { EditorState } from '../state';
 import { PreviewParams } from './PreviewParams';
@@ -27,7 +27,7 @@ const PREVIEW_OWNER = 'soundfx-preview';
  * only there to listen with.
  */
 export class SoundFxEditor extends AssetTabEditor<SoundFxAsset, GraphCanvas> {
-  readonly snap = new SnapToggle(() => this.canvas);
+  readonly snap = new SnapToggle(() => this.canvas, GRAPH_SNAPS_AT_FIRST);
   /** Public for the check scripts. */
   readonly soundPicker: Dropdown;
   readonly playButton: Button;

src/editor/statemachine/StateMachineEditor.ts

@@ -2,7 +2,7 @@ import { statesOf } from '../../core/graph';
 import type { Asset, StateMachineAsset } from '../../core/model/Asset';
 import { AssetTabEditor } from '../AssetTabEditor';
 import { GraphCanvas } from '../graph/GraphCanvas';
-import { SnapToggle } from '../graph/SnapToggle';
+import { GRAPH_SNAPS_AT_FIRST, SnapToggle } from '../graph/SnapToggle';
 import type { EditorState } from '../state';
 
 /** Room kept for the "N states" readout. */
@@ -14,7 +14,7 @@ const INFO_WIDTH = 90;
  * and undo are all the graph's.
  */
 export class StateMachineEditor extends AssetTabEditor<StateMachineAsset, GraphCanvas> {
-  readonly snap = new SnapToggle(() => this.canvas);
+  readonly snap = new SnapToggle(() => this.canvas, GRAPH_SNAPS_AT_FIRST);
 
   constructor(state: EditorState) {
     super(state, { infoWidth: INFO_WIDTH });