wp-build: Replace getter-based exports with data properties

packages/wp-build/lib/build.mjs

@@ -564,11 +564,35 @@ async function bundlePackage( packageName, options = {} ) {
 			globalName,
 		};
 
-		// For packages with default exports, add a footer to properly expose the default
+		// Compose the footer in pieces:
+		//   1. If the package has a default export, unwrap the namespace so
+		//      `globalName` IS the default value.
+		//   2. For every package that exposes a global namespace, replace
+		//      esbuild's getter-based re-exports with direct data properties.
+		//      esbuild emits each export as `Object.defineProperty(ns, k,
+		//      { get: () => binding })` to preserve ESM live-binding semantics
+		//      across hoisting; consumers then pay a getter call on every
+		//      property access. Across the editor mount that's hundreds of
+		//      thousands of getter invocations (every hook, every selector).
+		//      Once the IIFE has finished, the bindings are stable, so we can
+		//      read each getter once and replace it with a plain data
+		//      property — same value, ~2x cheaper per access in V8.
+		const footerParts = [];
 		if ( packageJson.wpScriptDefaultExport && globalName ) {
-			baseConfig.footer = {
-				js: `if (typeof ${ globalName } === 'object' && ${ globalName }.default) { ${ globalName } = ${ globalName }.default; }`,
-			};
+			footerParts.push(
+				`if (typeof ${ globalName } === 'object' && ${ globalName }.default) { ${ globalName } = ${ globalName }.default; }`
+			);
+		}
+		if ( globalName ) {
+			// esbuild marks the getters non-configurable, so we can't rewrite
+			// them in place; replacing the whole namespace with a shallow
+			// copy is the simplest way to materialize each value once.
+			footerParts.push(
+				`if(${ globalName }&&typeof ${ globalName }==='object'){${ globalName }=Object.assign({},${ globalName });}`
+			);
+		}
+		if ( footerParts.length ) {
+			baseConfig.footer = { js: footerParts.join( '' ) };
 		}
 
 		const baseBundlePlugins = [