Fix text layout without CanvasKit: estimate size instead of 100×100 default

Text nodes with textAutoResize=WIDTH_AND_HEIGHT kept their 100×100
default SceneNode size when MeasureFunc was unavailable (no CanvasKit),
blowing up every HUG container.

Add fallback estimator (~0.6 × fontSize per char) in layout.ts so
headless layout produces sane sizes.

DO NOT change textAutoResize defaults in renderer.ts without testing
headless layout — see comments there and in layout.ts.

packages/core/src/layout.ts

@@ -23,6 +23,8 @@ export type TextMeasurer = (
 
 let globalTextMeasurer: TextMeasurer | null = null
 
+const GLYPH_WIDTH_FACTOR = 0.6
+
 export function setTextMeasurer(measurer: TextMeasurer | null): void {
   globalTextMeasurer = measurer
 }
@@ -343,6 +345,15 @@ function configureChildAsLeaf(yogaChild: YogaNode, child: SceneNode, parent: Sce
 
   if (needsMeasureFunc) {
     configureTextLeaf(yogaChild, child, parent)
+  } else if (isText && !globalTextMeasurer && child.textAutoResize !== 'NONE') {
+    const est = estimateTextSize(child)
+    if (child.textAutoResize === 'WIDTH_AND_HEIGHT') {
+      yogaChild.setWidth(est.width)
+      yogaChild.setHeight(est.height)
+    } else if (child.textAutoResize === 'HEIGHT') {
+      yogaChild.setWidth(child.width)
+      yogaChild.setHeight(est.height)
+    }
   } else {
     configureNonTextLeaf(yogaChild, child, isRow, stretchCross)
   }
@@ -353,6 +364,18 @@ function configureChildAsLeaf(yogaChild: YogaNode, child: SceneNode, parent: Sce
   applyMinMaxConstraints(yogaChild, child)
 }
 
+// Fallback text size estimate when CanvasKit is unavailable (headless/tests).
+// Without this, text nodes keep their 100×100 default and blow up HUG containers.
+function estimateTextSize(node: SceneNode): { width: number; height: number } {
+  const fontSize = node.fontSize || 14
+  const lineHeight = fontSize * 1.2
+  const charWidth = fontSize * GLYPH_WIDTH_FACTOR
+  return {
+    width: Math.ceil(node.text.length * charWidth),
+    height: Math.ceil(lineHeight)
+  }
+}
+
 function configureTextLeaf(
   yogaChild: YogaNode,
   child: SceneNode,

packages/core/src/render/renderer.ts

@@ -401,6 +401,7 @@ function applyTextOverrides(
   const fillsParent = w === 'fill' || (props.grow as number) > 0
   const isInsideAutoLayout = parentLayout !== 'NONE'
 
+  // Coupled with estimateTextSize() in layout.ts — test headless layout after changes.
   if (props.textAutoResize) {
     o.textAutoResize = TEXT_AUTO_RESIZE_MAP[props.textAutoResize as string] ?? 'NONE'
   } else if (hasExplicitWidth || (isInsideAutoLayout && fillsParent)) {

tests/engine/layout.test.ts

@@ -1020,7 +1020,7 @@ describe('Auto Layout', () => {
       expect(updatedArrow2.x).toBe(190)
     })
 
-    test('without measurer, text keeps its existing width', () => {
+    test('without measurer, text uses estimated size instead of 100x100 default', () => {
       const graph = new SceneGraph()
       const pid = pageId(graph)
 
@@ -1045,7 +1045,11 @@ describe('Auto Layout', () => {
       computeAllLayouts(graph)
 
       const updatedText = graph.getNode(text.id)!
-      expect(updatedText.width).toBe(200)
+      // Rough estimate: ~0.6 × fontSize × charCount, not the 100×100 default
+      expect(updatedText.width).toBeLessThan(100)
+      expect(updatedText.width).toBeGreaterThan(0)
+      expect(updatedText.height).toBeLessThan(100)
+      expect(updatedText.height).toBeGreaterThan(0)
     })
 
     test('HEIGHT auto-resize text wraps via MeasureFunc when filling parent', () => {