Add ESLint and Prettier, and close the node test gaps

Tooling:
- Prettier as the single formatting authority (110 columns, single quotes,
  measured against the existing style); Markdown excluded because table-cell
  padding turns the README glossary into 1000-character lines.
- Type-aware ESLint ending in eslint-config-prettier, so a rule always means
  "this is a bug", never "this looks different".
- .editorconfig and an `npm run check` that runs typecheck, lint, format and
  tests in one go.

Findings fixed on the first run: three more duplicate imports, four
String(unknown) calls (parameter types narrowed instead of casts), two dead
initialisers, two redundant casts, a console.log for a real error. Two
warnings were false here and are disabled with a reason in place.

Tests 132 -> 269:
- node-catalog.test.ts covers every node with a run(), with a guard that fails
  when a new node has no row.
- behavior-events.test.ts covers the ten event nodes through a running World,
  checking timing rather than existence.
- Input's state machine (press/release/releaseAll) is reachable without DOM
  events now; the DOM handlers are thin adapters.

Compare fell back to == without a configured operator although the schema
default is <; aligned.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/ui/widgets/Button.ts

@@ -34,7 +34,9 @@ export class Button extends Widget {
     this.addChild(this.bg, this.labelText);
 
     // Leaving while pressed cancels the click: a release elsewhere must not activate.
-    this.trackHover(() => { this.pressed = false; });
+    this.trackHover(() => {
+      this.pressed = false;
+    });
     this.on('pointerdown', (e: FederatedPointerEvent) => {
       if (e.button !== 0) return;
       this.pressed = true;
@@ -89,10 +91,22 @@ export class Button extends Widget {
     const flat = this.variant === 'default' || this.variant === 'ghost';
     let fill: number | null = c.control;
     let border: number | null = c.border;
-    if (this.variant === 'primary') { fill = c.accent; border = null; }
-    if (this.variant === 'danger') { fill = c.danger; border = null; }
-    if (this.variant === 'ghost') { fill = null; border = null; }
-    if (this.toggled) { fill = c.accent; border = null; }
+    if (this.variant === 'primary') {
+      fill = c.accent;
+      border = null;
+    }
+    if (this.variant === 'danger') {
+      fill = c.danger;
+      border = null;
+    }
+    if (this.variant === 'ghost') {
+      fill = null;
+      border = null;
+    }
+    if (this.toggled) {
+      fill = c.accent;
+      border = null;
+    }
     if (this.hovered && !this.toggled && flat) fill = c.controlHover;
     if (this.pressed && flat) fill = c.controlActive;
     const stroke = this.focused ? c.accent : border;

src/ui/widgets/Checkbox.ts

@@ -54,7 +54,11 @@ export class Checkbox extends Widget {
       y,
     });
     if (this.checked) {
-      this.box.moveTo(4, y + 8.5).lineTo(7, y + 11.5).lineTo(12.5, y + 5).stroke({ width: 2, color: c.accentText });
+      this.box
+        .moveTo(4, y + 8.5)
+        .lineTo(7, y + 11.5)
+        .lineTo(12.5, y + 5)
+        .stroke({ width: 2, color: c.accentText });
     }
   }
 }

src/ui/widgets/ColorPicker.ts

@@ -54,7 +54,9 @@ export class ColorPicker extends Popup {
       this.applyPointer(local.x, local.y);
     });
     // The press starts on the body; its release bubbles up to the popup either way.
-    this.onPointerRelease(() => { this.dragging = null; });
+    this.onPointerRelease(() => {
+      this.dragging = null;
+    });
     this.content.add(this.body);
     this.renderSv();
   }

src/ui/widgets/Dialog.ts

@@ -22,7 +22,9 @@ export class Dialog extends Popup {
     const row = new HStack({ gap: Theme.gap, align: 'center' });
     row.add(new Spacer(), 1); // pushes the buttons to the right
     for (const b of buttons) {
-      const button = new Button(b.label, { variant: b.primary ? 'primary' : b.danger ? 'danger' : 'default' });
+      const button = new Button(b.label, {
+        variant: b.primary ? 'primary' : b.danger ? 'danger' : 'default',
+      });
       button.onClick = this.closeThen(b.onClick);
       row.add(button);
     }

src/ui/widgets/ListRow.ts

@@ -20,7 +20,11 @@ export class ListRow extends Widget {
   private selected = false;
   private listFocused = false;
 
-  constructor(readonly item: ListItem, height: number, private readonly chevronSlot: boolean) {
+  constructor(
+    readonly item: ListItem,
+    height: number,
+    private readonly chevronSlot: boolean,
+  ) {
     super();
     this.cursor = 'pointer';
     this.minHeight = height;
@@ -59,12 +63,17 @@ export class ListRow extends Widget {
     const depth = this.item.depth ?? 0;
     const indent = this.indent;
     this.bg.clear();
-    if (this.selected) this.bg.rect(0, 0, this.w, this.h).fill(this.listFocused ? c.selection : c.controlActive);
+    if (this.selected)
+      this.bg.rect(0, 0, this.w, this.h).fill(this.listFocused ? c.selection : c.controlActive);
     else if (this.hovered) this.bg.rect(0, 0, this.w, this.h).fill(c.controlHover);
     // Tree guide: a short "└" mark in front of nested rows.
     if (depth > 0) {
       const gx = indent - 8;
-      this.bg.moveTo(gx, 0).lineTo(gx, this.h / 2).lineTo(indent - 2, this.h / 2).stroke({ width: 1, color: c.border });
+      this.bg
+        .moveTo(gx, 0)
+        .lineTo(gx, this.h / 2)
+        .lineTo(indent - 2, this.h / 2)
+        .stroke({ width: 1, color: c.border });
     }
     let x = indent;
     if (this.chevronSlot) {
@@ -86,13 +95,26 @@ export class ListRow extends Widget {
     const hintW = this.hint.text ? this.hint.width + Theme.padding : 0;
     this.labelText.text = truncate(this.item.label, this.labelText.style, this.w - x - hintW - Theme.padding);
     this.labelText.position.set(x, centreY(this.h, this.labelText.height));
-    this.hint.position.set(Math.round(this.w - Theme.padding - this.hint.width), centreY(this.h, this.hint.height));
+    this.hint.position.set(
+      Math.round(this.w - Theme.padding - this.hint.width),
+      centreY(this.h, this.hint.height),
+    );
   }
 
   /** ▸ when collapsed, ▾ when expanded – drawn, not glyphs, so it stays crisp at any size. */
   private drawChevron(x: number, y: number, expanded: boolean): void {
     const color = this.selected ? Theme.colors.text : Theme.colors.textMuted;
-    if (expanded) this.bg.moveTo(x - 3, y - 2).lineTo(x + 5, y - 2).lineTo(x + 1, y + 3).fill(color);
-    else this.bg.moveTo(x - 1, y - 4).lineTo(x + 4, y).lineTo(x - 1, y + 4).fill(color);
+    if (expanded)
+      this.bg
+        .moveTo(x - 3, y - 2)
+        .lineTo(x + 5, y - 2)
+        .lineTo(x + 1, y + 3)
+        .fill(color);
+    else
+      this.bg
+        .moveTo(x - 1, y - 4)
+        .lineTo(x + 4, y)
+        .lineTo(x - 1, y + 4)
+        .fill(color);
   }
 }

src/ui/widgets/NumberField.ts

@@ -124,6 +124,8 @@ export class NumberField extends TextField {
 
   /** Clamps to min/max; NaN/Infinity keep the current value (0 before the first assignment). */
   private clampValue(value: number): number {
+    // `?? 0` is not dead despite the type: the constructor calls this before assigning `numeric`.
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (!Number.isFinite(value)) return this.numeric ?? 0;
     return clamp(value, this.min, this.max);
   }

src/ui/widgets/ScrollContainer.ts

@@ -39,7 +39,9 @@ export class ScrollContainer extends Widget {
       this.scrollTo(this.dragScrollStart + (e.global.y - this.dragStart) * ratio);
     });
     // The press starts on the scrollbar graphics; its release bubbles up to us either way.
-    this.onPointerRelease(() => { this.draggingBar = false; });
+    this.onPointerRelease(() => {
+      this.draggingBar = false;
+    });
   }
 
   /** Replaces the scrolled widget. The previous content is detached, not destroyed. */
@@ -99,6 +101,8 @@ export class ScrollContainer extends Widget {
     const x = this.w - trackW - 2;
     const barH = Math.max(20, (this.h / this.contentHeight) * this.h);
     const barY = (this.scrollY / this.maxScroll) * (this.h - barH);
-    this.scrollbar.roundRect(x, barY, trackW, barH, trackW / 2).fill({ color: Theme.colors.textMuted, alpha: 0.6 });
+    this.scrollbar
+      .roundRect(x, barY, trackW, barH, trackW / 2)
+      .fill({ color: Theme.colors.textMuted, alpha: 0.6 });
   }
 }

src/ui/widgets/TextField.ts

@@ -61,7 +61,14 @@ export class TextField extends Widget implements TextEditTarget {
     this.minWidth = options.width ?? 80;
     this.textNode = new Text({ text: value, style: textStyle(options.style ?? 'body') });
     this.placeholderNode = new Text({ text: this.placeholder, style: textStyle('muted') });
-    this.addChild(this.bg, this.selectionShape, this.placeholderNode, this.textNode, this.caret, this.clipShape);
+    this.addChild(
+      this.bg,
+      this.selectionShape,
+      this.placeholderNode,
+      this.textNode,
+      this.caret,
+      this.clipShape,
+    );
     this.mask = this.clipShape;
 
     this.trackHover();
@@ -71,7 +78,9 @@ export class TextField extends Widget implements TextEditTarget {
       const index = this.indexAt(this.toLocal(e.global).x);
       this.setSelection(this.selStart, index, true);
     });
-    this.onPointerRelease(() => { this.dragSelecting = false; });
+    this.onPointerRelease(() => {
+      this.dragSelecting = false;
+    });
   }
 
   /** Current text, including an edit in progress that has not been committed yet. */
@@ -216,7 +225,10 @@ export class TextField extends Widget implements TextEditTarget {
     let bestDist = Infinity;
     for (let i = 0; i <= this.valueText.length; i++) {
       const dist = Math.abs(this.textWidth(this.valueText.slice(0, i)) - x);
-      if (dist < bestDist) { bestDist = dist; best = i; }
+      if (dist < bestDist) {
+        bestDist = dist;
+        best = i;
+      }
     }
     return best;
   }
@@ -248,7 +260,10 @@ export class TextField extends Widget implements TextEditTarget {
       fill: this.hovered && !this.editing ? c.controlHover : c.control,
       border: this.focused ? c.accent : c.border,
     });
-    this.clipShape.clear().rect(1, 1, this.w - 2, this.h - 2).fill(0xffffff);
+    this.clipShape
+      .clear()
+      .rect(1, 1, this.w - 2, this.h - 2)
+      .fill(0xffffff);
 
     this.textNode.text = this.valueText;
     this.placeholderNode.text = this.valueText ? '' : this.placeholder;
@@ -271,7 +286,9 @@ export class TextField extends Widget implements TextEditTarget {
     if (hi > lo) {
       const x1 = textX + this.textWidth(this.valueText.slice(0, lo));
       const x2 = textX + this.textWidth(this.valueText.slice(0, hi));
-      this.selectionShape.rect(x1, textY, x2 - x1, this.textNode.height).fill({ color: c.accent, alpha: 0.45 });
+      this.selectionShape
+        .rect(x1, textY, x2 - x1, this.textNode.height)
+        .fill({ color: c.accent, alpha: 0.45 });
     }
     if (this.caretVisible) {
       this.caret.rect(Math.round(textX + caretX), textY, 1, this.textNode.height).fill(c.text);