fix(cli): handle missing yoga-layout WASM files gracefully

Add existence checks before reading yoga.wasm and yoga.js files.
Generate placeholder yoga-sync.mjs with minimal API when WASM files
are not available (e.g., in CI without WASM build).

Follows same pattern as extract-minilm-model.mjs which already has
graceful degradation for missing AI models.

Author: jdalton

packages/cli/scripts/extract-yoga-wasm.mjs

@@ -6,7 +6,7 @@
  * Idempotent: Skips regeneration if source hasn't changed (supports CI caching).
  */
 
-import { readFileSync, writeFileSync } from 'node:fs'
+import { existsSync, readFileSync, writeFileSync } from 'node:fs'
 import path from 'node:path'
 import { fileURLToPath } from 'node:url'
 
@@ -39,6 +39,43 @@ if (
   process.exit(0)
 }
 
+// Check if yoga-layout WASM files exist.
+if (!existsSync(yogaWasmFile) || !existsSync(yogaJsFile)) {
+  // Graceful fallback: Generate placeholder for CI builds without WASM.
+  logger.warn('yoga-layout WASM not built yet, generating placeholder')
+
+  const placeholderContent = `/**
+ * Synchronous yoga-layout with embedded WASM binary (Placeholder).
+ *
+ * This file is AUTO-GENERATED by scripts/extract-yoga-wasm.mjs
+ * DO NOT EDIT MANUALLY - changes will be overwritten on next build.
+ *
+ * NOTE: This is a placeholder build. Run 'pnpm build' in yoga-layout first.
+ */
+
+// Placeholder yoga export with minimal API.
+const yoga = {
+  Config: class Config {},
+  Node: class Node {
+    static create() {
+      return new Node()
+    }
+    calculateLayout() {}
+    getComputedLayout() {
+      return { left: 0, top: 0, width: 0, height: 0 }
+    }
+  },
+}
+
+export default yoga
+`
+
+  ensureOutputDir(outputPath)
+  writeFileSync(outputPath, placeholderContent, 'utf-8')
+  logger.log(`✓ Generated placeholder ${outputPath}`)
+  process.exit(0)
+}
+
 // Read WASM binary and convert to base64.
 const wasmBinary = readFileSync(yogaWasmFile)
 const base64Data = wasmBinary.toString('base64')