diff --git a/Gruntfile.js b/Gruntfile.js
index 2ce79d03bddc6..dae8c3e972e4c 100644
--- a/Gruntfile.js
+++ b/Gruntfile.js
@@ -41,18 +41,43 @@ module.exports = function(grunt) {
 			'wp-admin/css/colors/**/*.css',
 		],
 
-		// Built js files, in /src or /build.
+		// Built JavaScript files that do not belong to a more specific group.
 		jsFiles = [
 			'wp-admin/js/',
-			'wp-includes/js/',
+			'wp-includes/js/*',
+			/*
+			 * This directory has shared responsibility and is managed through
+			 * gutenbergUnversionedFiles, webpackFiles, and copy:vendor-js.
+			 */
+			'!wp-includes/js/dist',
+			'wp-includes/js/dist/vendor/*.js',
+			// Managed by the Gutenberg-related tasks.
+			'!wp-includes/js/dist/vendor/react-jsx-runtime*',
+		],
+
+		// Files sourced from the Gutenberg repository built asset that are ignored by version control.
+		gutenbergUnversionedFiles = [
+			SOURCE_DIR + 'wp-includes/blocks/*/*.css',
+			SOURCE_DIR + 'wp-includes/css/dist',
+			SOURCE_DIR + 'wp-includes/js/dist/*.js',
+			SOURCE_DIR + 'wp-includes/js/dist/script-modules',
+			SOURCE_DIR + 'wp-includes/js/dist/vendor/react-jsx-runtime*',
 		],
 
-		// All files copied from the Gutenberg repository excluded from version control.
-		gutenbergFiles = [
-			'wp-includes/js/dist',
-			'wp-includes/css/dist',
-			// Old location kept temporarily to ensure they are cleaned up.
-			'wp-includes/icons',
+		// Files sourced from the Gutenberg repository built asset that are managed through version control.
+		gutenbergVersionedFiles = [
+			// Block assets (block.json, top-level PHP, nested PHP helpers).
+			SOURCE_DIR + 'wp-includes/blocks/*',
+			'!' + SOURCE_DIR + 'wp-includes/blocks/index.php',
+			SOURCE_DIR + 'wp-includes/images/icon-library',
+			SOURCE_DIR + 'wp-includes/theme.json',
+			SOURCE_DIR + 'wp-includes/theme-i18n.json',
+			// Routes and pages.
+			SOURCE_DIR + 'wp-includes/build',
+			// PHP manifests generated by gutenberg:copy.
+			SOURCE_DIR + 'wp-includes/assets/icon-library-manifest.php',
+			SOURCE_DIR + 'wp-includes/assets/script-loader-packages.php',
+			SOURCE_DIR + 'wp-includes/assets/script-modules-packages.php',
 		],
 
 		// All files built by Webpack, in /src or /build.
@@ -241,10 +266,32 @@ module.exports = function(grunt) {
 				return setFilePath( WORKING_DIR, file );
 			} ),
 
-			// Clean files built by the tools/gutenberg scripts.
-			gutenberg: gutenbergFiles.map( function( file ) {
-				return setFilePath( WORKING_DIR, file );
-			}),
+			/*
+			 * Clean files sourced from the downloaded zip file built by the Gutenberg repository.
+			 *
+			 * All files originating from the Gutenberg repository's built assets (both tracked and untracked by version
+			 * control) are deleted when `clean:gutenberg` is explicitly called. This ensures that versioned files that
+			 * have been deleted upstream are also removed from version control in this repository.
+			 *
+			 * When `clean:gutenberg` is not explicitly called and run through `grunt clean`, only ignored files are
+			 * cleaned.
+			 */
+			gutenberg: {
+				get src() {
+					const cli = grunt.cli.tasks;
+					// Preserve versioned files only when running bare `grunt clean`.
+					const isBareCleanSweep =
+						cli.includes( 'clean' ) &&
+						! cli.includes( 'clean:gutenberg' );
+
+					if ( isBareCleanSweep ) {
+						return gutenbergUnversionedFiles;
+					} else {
+						return gutenbergUnversionedFiles.concat( gutenbergVersionedFiles );
+					}
+				},
+			},
+
 			dynamic: {
 				dot: true,
 				expand: true,
@@ -289,7 +336,6 @@ module.exports = function(grunt) {
 						expand: true,
 						cwd: SOURCE_DIR,
 						src: buildFiles.concat( [
-							'!wp-includes/assets/**', // Assets is extracted into separate copy tasks.
 							'!js/**', // JavaScript is extracted into separate copy tasks.
 							'!.{svn,git}', // Exclude version control folders.
 							'!wp-includes/version.php', // Exclude version.php.
@@ -666,24 +712,18 @@ module.exports = function(grunt) {
 						'constants.php',
 						'pages/**/*.php',
 					],
-					dest: WORKING_DIR + 'wp-includes/build/',
+					dest: SOURCE_DIR + 'wp-includes/build/',
 				} ],
 			},
 			/*
-			 * Only copy files relevant to the routes specified in the registry file.
-			 *
-			 * While the registry file does not contain any experimental routes, the `gutenberg/build/routes` directory
-			 * includes the files for all registered routes. Only the files related to the routes specified in the
-			 * registry should be included in the WordPress build.
-			 *
-			 * The `src` list is populated at task runtime by `routes:setup`, which reads the registry after
-			 * `gutenberg:download` has run. See the `routes:setup` task registration for implementation details.
+			 * The list of route source files is populated from the contents of the registry.php file at task runtime by
+			 * `routes:setup`.
 			 */
 			routes: {
 				expand: true,
 				cwd: 'gutenberg/build',
 				src: [],
-				dest: WORKING_DIR + 'wp-includes/build/',
+				dest: SOURCE_DIR + 'wp-includes/build/',
 			},
 			'gutenberg-js': {
 				files: [ {
@@ -692,7 +732,7 @@ module.exports = function(grunt) {
 					src: [
 						'pages/**/*.js',
 					],
-					dest: WORKING_DIR + 'wp-includes/build/',
+					dest: SOURCE_DIR + 'wp-includes/build/',
 				} ],
 			},
 			'gutenberg-modules': {
@@ -706,7 +746,7 @@ module.exports = function(grunt) {
 						// with no debugging value over the minified versions.
 						'!vips/!(*.min).js',
 					],
-					dest: WORKING_DIR + 'wp-includes/js/dist/script-modules/',
+					dest: SOURCE_DIR + 'wp-includes/js/dist/script-modules/',
 				} ],
 			},
 			'gutenberg-styles': {
@@ -719,7 +759,7 @@ module.exports = function(grunt) {
 						// Per-block CSS is copied to wp-includes/blocks/ by tools/gutenberg/copy.js.
 						'!block-library/*/**',
 					],
-					dest: WORKING_DIR + 'wp-includes/css/dist/',
+					dest: SOURCE_DIR + 'wp-includes/css/dist/',
 				} ],
 			},
 			'gutenberg-theme-json': {
@@ -738,11 +778,11 @@ module.exports = function(grunt) {
 				files: [
 					{
 						src: 'gutenberg/lib/theme.json',
-						dest: WORKING_DIR + 'wp-includes/theme.json',
+						dest: SOURCE_DIR + 'wp-includes/theme.json',
 					},
 					{
 						src: 'gutenberg/lib/theme-i18n.json',
-						dest: WORKING_DIR + 'wp-includes/theme-i18n.json',
+						dest: SOURCE_DIR + 'wp-includes/theme-i18n.json',
 					},
 				],
 			},
@@ -750,8 +790,8 @@ module.exports = function(grunt) {
 				files: [ {
 					expand: true,
 					cwd: 'gutenberg/packages/icons/src/library',
-					src: '*.svg',
-					dest: WORKING_DIR + 'wp-includes/images/icon-library',
+					src: [ '*.svg' ],
+					dest: SOURCE_DIR + 'wp-includes/images/icon-library',
 				} ],
 			},
 			'icon-library-manifest': {
@@ -773,7 +813,7 @@ module.exports = function(grunt) {
 				},
 				files: [ {
 					src: 'gutenberg/packages/icons/src/manifest.php',
-					dest: WORKING_DIR + 'wp-includes/assets/icon-library-manifest.php',
+					dest: SOURCE_DIR + 'wp-includes/assets/icon-library-manifest.php',
 				} ],
 			},
 		},
@@ -1667,7 +1707,7 @@ module.exports = function(grunt) {
 			 */
 			grunt.util.spawn( {
 				grunt: true,
-				args: [ 'build:gutenberg', '--dev' ],
+				args: [ 'build:gutenberg' ],
 				opts: { stdio: 'inherit' }
 			}, function( buildError ) {
 				done( ! buildError );
@@ -1677,10 +1717,9 @@ module.exports = function(grunt) {
 
 	grunt.registerTask( 'gutenberg:copy', 'Copies Gutenberg JS packages and block assets to WordPress Core.', function() {
 		const done = this.async();
-		const buildDir = grunt.option( 'dev' ) ? 'src' : 'build';
 		grunt.util.spawn( {
 			cmd: 'node',
-			args: [ 'tools/gutenberg/copy.js', `--build-dir=${ buildDir }` ],
+			args: [ 'tools/gutenberg/copy.js' ],
 			opts: { stdio: 'inherit' }
 		}, function( error ) {
 			done( ! error );
@@ -2164,10 +2203,23 @@ module.exports = function(grunt) {
 		} );
 	} );
 
-	grunt.registerTask( 'build:gutenberg', [
-		'copy:gutenberg-php',
+	// Detects and copies stable routes.
+	grunt.registerTask( 'build:routes', [
 		'routes:setup',
 		'copy:routes',
+	] );
+
+	/*
+	 * Refresh the Gutenberg-sourced content in src/.
+	 *
+	 * clean:gutenberg must run first to ensure files removed upstream are purged.
+	 *
+	 * Because all of these tasks write to src/, the outcome is identical for build and build:dev.
+	 */
+	grunt.registerTask( 'build:gutenberg', [
+		'clean:gutenberg',
+		'copy:gutenberg-php',
+		'build:routes',
 		'copy:gutenberg-js',
 		'gutenberg:copy',
 		'copy:gutenberg-modules',
@@ -2181,21 +2233,21 @@ module.exports = function(grunt) {
 		if ( grunt.option( 'dev' ) ) {
 			grunt.task.run( [
 				'gutenberg:verify',
+				'build:gutenberg',
 				'build:js',
 				'build:css',
 				'build:codemirror',
-				'build:gutenberg',
 				'build:certificates'
 			] );
 		} else {
 			grunt.task.run( [
 				'gutenberg:verify',
+				'build:gutenberg',
 				'build:certificates',
 				'build:files',
 				'build:js',
 				'build:css',
 				'build:codemirror',
-				'build:gutenberg',
 				'replace:source-maps',
 				'verify:build'
 			] );
diff --git a/package.json b/package.json
index 430efdd2fba85..429e0469dd491 100644
--- a/package.json
+++ b/package.json
@@ -141,6 +141,6 @@
 		"typecheck:php": "node ./tools/local-env/scripts/docker.js run --rm php composer phpstan",
 		"gutenberg:copy": "node tools/gutenberg/copy.js",
 		"gutenberg:verify": "node tools/gutenberg/utils.js",
-		"gutenberg:download": "node tools/gutenberg/download.js && grunt build:gutenberg --dev"
+		"gutenberg:download": "node tools/gutenberg/download.js && grunt build:gutenberg"
 	}
 }
diff --git a/tools/gutenberg/copy.js b/tools/gutenberg/copy.js
index 8589c9581bed1..3da78e4b14611 100644
--- a/tools/gutenberg/copy.js
+++ b/tools/gutenberg/copy.js
@@ -6,32 +6,59 @@
  * This script copies and transforms Gutenberg's build output to WordPress Core.
  * It handles path transformations from plugin structure to Core structure.
  *
+ * Since a number of files sourced from the downloaded zip file are subject to
+ * version control, the `src/` directory is used as the destination for all
+ * outputs of this file (both versioned and unversioned).
+ *
+ * Grunt will copy the files appropriately when running `build` instead of
+ * `build:dev`, and the repository's configured ignore rules will manage what
+ * can be committed.
+ *
  * @package WordPress
  */
 
 const fs = require( 'fs' );
 const path = require( 'path' );
-const json2php = require( 'json2php' );
+const json2php = /** @type {typeof import('json2php').default} */ (
+	/** @type {unknown} */ ( require( 'json2php' ) )
+);
 const { fromString } = require( 'php-array-reader' );
 
-// Paths.
 const rootDir = path.resolve( __dirname, '../..' );
 const gutenbergDir = path.join( rootDir, 'gutenberg' );
 const gutenbergBuildDir = path.join( gutenbergDir, 'build' );
+const wpIncludesDir = path.join( rootDir, 'src', 'wp-includes' );
+
+/**
+ * JS package copy configuration.
+ *
+ * @typedef ScriptsConfig
+ * @type {object}
+ * @property {string}                 source           - Gutenberg-relative source directory (e.g. `'scripts'`).
+ * @property {string}                 destination      - Subpath under `wp-includes/` where packages land (e.g. `'js/dist'`).
+ * @property {boolean}                copyDirectories  - Whether to copy whole directories (with optional renames) as-is.
+ * @property {Record<string, string>} directoryRenames - Map of source directory name → destination directory name.
+ */
 
-/*
- * Determine build target from command line argument (--dev or --build-dir).
- * Default to 'src' for development.
+/**
+ * One block family entry — block library, widget blocks, etc.
+ *
+ * @typedef BlockConfigSource
+ * @type {object}
+ * @property {string} name    - Human-readable label (e.g. `'block-library'`, `'widgets'`).
+ * @property {string} scripts - Gutenberg-relative path to the block scripts directory.
+ * @property {string} styles  - Gutenberg-relative path to the block styles directory.
+ * @property {string} php     - Gutenberg-relative path to the block PHP directory.
  */
-const args = process.argv.slice( 2 );
-const buildDirArg = args.find( ( arg ) => arg.startsWith( '--build-dir=' ) );
-const buildTarget = buildDirArg
-	? buildDirArg.split( '=' )[ 1 ]
-	: args.includes( '--dev' )
-	? 'src'
-	: 'build';
 
-const wpIncludesDir = path.join( rootDir, buildTarget, 'wp-includes' );
+/**
+ * Block copy configuration.
+ *
+ * @typedef BlockConfig
+ * @type {object}
+ * @property {string}              destination - Subpath under `wp-includes/` where blocks land (e.g. `'blocks'`).
+ * @property {BlockConfigSource[]} sources     - One entry per block family.
+ */
 
 /**
  * Copy configuration.
@@ -81,7 +108,7 @@ const COPY_CONFIG = {
  * @throws Error when PHP source file unable to be read or parsed.
  *
  * @param {string} phpFilepath Absolute path of PHP file returning a single value.
- * @return {Object|Array} JavaScript representation of value from input file.
+ * @return {any} JavaScript representation of value from input file.
  */
 function readReturnedValueFromPHPFile( phpFilepath ) {
 	const content = fs.readFileSync( phpFilepath, 'utf8' );
@@ -109,104 +136,244 @@ function isExperimentalBlock( blockJsonPath ) {
 }
 
 /**
- * Copy all assets for blocks from Gutenberg to Core.
- * Handles scripts, styles, PHP, and JSON for all block types in a unified way.
+ * Generate a list of stable blocks.
  *
- * @param {Object} config - Block configuration from COPY_CONFIG.blocks
+ * Blocks marked as `"__experimental": true` in a `block.json` file are excluded.
+ *
+ * @param {string} scriptsSrc - Path to the Gutenberg scripts source (e.g. `scripts/block-library`).
+ * @return {string[]} Stable block directory names.
  */
-function copyBlockAssets( config ) {
-	const blocksDest = path.join( wpIncludesDir, config.destination );
+function getStableBlocks( scriptsSrc ) {
+	if ( ! fs.existsSync( scriptsSrc ) ) {
+		return [];
+	}
+	return fs
+		.readdirSync( scriptsSrc, { withFileTypes: true } )
+		.filter( ( entry ) => entry.isDirectory() )
+		.map( ( entry ) => entry.name )
+		.filter( ( blockName ) => ! isExperimentalBlock(
+			path.join( scriptsSrc, blockName, 'block.json' )
+		) );
+}
 
-	for ( const source of config.sources ) {
-		const scriptsSrc = path.join( gutenbergBuildDir, source.scripts );
-		const stylesSrc = path.join( gutenbergBuildDir, source.styles );
-		const phpSrc = path.join( gutenbergBuildDir, source.php );
+/**
+ * Copy JavaScript files.
+ *
+ * @param {ScriptsConfig} config - Scripts configuration from `COPY_CONFIG.scripts`.
+ */
+function copyScripts( config ) {
+	const scriptsSrc = path.join( gutenbergBuildDir, config.source );
+	const scriptsDest = path.join( wpIncludesDir, config.destination );
 
-		if ( ! fs.existsSync( scriptsSrc ) ) {
-			continue;
-		}
+	if ( ! fs.existsSync( scriptsSrc ) ) {
+		return;
+	}
 
-		// Get all block directories from the scripts source.
-		const blockDirs = fs
-			.readdirSync( scriptsSrc, { withFileTypes: true } )
-			.filter( ( entry ) => entry.isDirectory() )
-			.map( ( entry ) => entry.name );
-
-		for ( const blockName of blockDirs ) {
-			// Skip experimental blocks.
-			const blockJsonPath = path.join(
-				scriptsSrc,
-				blockName,
-				'block.json'
-			);
-			if ( isExperimentalBlock( blockJsonPath ) ) {
-				continue;
+	const entries = fs.readdirSync( scriptsSrc, { withFileTypes: true } );
+
+	for ( const entry of entries ) {
+		const src = path.join( scriptsSrc, entry.name );
+
+		if ( entry.isDirectory() ) {
+			// Check if this should be copied as a directory (like vendors/).
+			if (
+				config.copyDirectories &&
+				config.directoryRenames &&
+				config.directoryRenames[ entry.name ]
+			) {
+				/*
+				 * Copy special directories with rename (vendors/ → vendor/).
+				 * Only copy react-jsx-runtime from vendors (react and react-dom come from Core's node_modules).
+				 */
+				const destName = config.directoryRenames[ entry.name ];
+				const dest = path.join( scriptsDest, destName );
+
+				if ( entry.name === 'vendors' ) {
+					// Only copy react-jsx-runtime files, skip react and react-dom.
+					const vendorFiles = fs.readdirSync( src );
+					let copiedCount = 0;
+					fs.mkdirSync( dest, { recursive: true } );
+					for ( const file of vendorFiles ) {
+						if (
+							file.startsWith( 'react-jsx-runtime' ) &&
+							file.endsWith( '.js' )
+						) {
+							const srcFile = path.join( src, file );
+							const destFile = path.join( dest, file );
+
+							fs.copyFileSync( srcFile, destFile );
+							copiedCount++;
+						}
+					}
+					console.log(
+						`   ✅ ${ entry.name }/ → ${ destName }/ (react-jsx-runtime only, ${ copiedCount } files)`
+					);
+				}
+			} else {
+				/*
+				 * Flatten package structure: package-name/index.js → package-name.js.
+				 * This matches Core's expected file structure.
+				 */
+				const packageFiles = fs.readdirSync( src );
+
+				for ( const file of packageFiles ) {
+					if ( /^index\.(js|min\.js)$/.test( file ) ) {
+						const srcFile = path.join( src, file );
+						// Replace 'index.' with 'package-name.'.
+						const destFile = file.replace(
+							/^index\./,
+							`${ entry.name }.`
+						);
+						const destPath = path.join( scriptsDest, destFile );
+
+						fs.mkdirSync( path.dirname( destPath ), {
+							recursive: true,
+						} );
+
+						fs.copyFileSync( srcFile, destPath );
+					}
+				}
 			}
+		} else if ( entry.isFile() && entry.name.endsWith( '.js' ) ) {
+			// Copy root-level JS files.
+			const dest = path.join( scriptsDest, entry.name );
+			fs.mkdirSync( path.dirname( dest ), { recursive: true } );
+			fs.copyFileSync( src, dest );
+		}
+	}
+
+	console.log( '   ✅ JavaScript packages copied' );
+}
 
+/**
+ * Copy `block.json` files for every stable block.
+ *
+ * @param {BlockConfig} config - Block configuration from `COPY_CONFIG.blocks`.
+ */
+function copyBlockJson( config ) {
+	const blocksDest = path.join( wpIncludesDir, config.destination );
+
+	for ( const source of config.sources ) {
+		const scriptsSrc = path.join( gutenbergBuildDir, source.scripts );
+		const blocks = getStableBlocks( scriptsSrc );
+
+		for ( const blockName of blocks ) {
+			const blockSrc = path.join( scriptsSrc, blockName );
 			const blockDest = path.join( blocksDest, blockName );
 			fs.mkdirSync( blockDest, { recursive: true } );
 
-			// 1. Copy scripts/JSON (everything except PHP)
-			const blockScriptsSrc = path.join( scriptsSrc, blockName );
-			if ( fs.existsSync( blockScriptsSrc ) ) {
-				fs.cpSync(
-					blockScriptsSrc,
-					blockDest,
-					{
-						recursive: true,
-						// Skip PHP, copied from build in steps 3 & 4.
-						filter: f => ! f.endsWith( '.php' ),
-					}
+			const blockJsonSrc = path.join( blockSrc, 'block.json' );
+			if ( fs.existsSync( blockJsonSrc ) ) {
+				fs.copyFileSync(
+					blockJsonSrc,
+					path.join( blockDest, 'block.json' )
 				);
 			}
+		}
 
-			// 2. Copy styles (if they exist in per-block directory)
-			const blockStylesSrc = path.join( stylesSrc, blockName );
-			if ( fs.existsSync( blockStylesSrc ) ) {
-				const cssFiles = fs
-					.readdirSync( blockStylesSrc )
-					.filter( ( file ) => file.endsWith( '.css' ) );
-				for ( const cssFile of cssFiles ) {
-					fs.copyFileSync(
-						path.join( blockStylesSrc, cssFile ),
-						path.join( blockDest, cssFile )
-					);
-				}
-			}
+		console.log(
+			`   ✅ ${ source.name } block.json copied (${ blocks.length } blocks)`
+		);
+	}
+}
 
-			// 3. Copy PHP from build
-			const blockPhpSrc = path.join( phpSrc, `${ blockName }.php` );
-			const phpDest = path.join(
-				wpIncludesDir,
-				config.destination,
-				`${ blockName }.php`
-			);
-			if ( fs.existsSync( blockPhpSrc ) ) {
-				fs.copyFileSync( blockPhpSrc, phpDest );
+/**
+ * Copy block PHP files for every stable block.
+ *
+ * Handles both the top-level `<block>.php` dynamic block files and any nested
+ * `*.php` helpers under `<block>/` (e.g. `navigation-link/shared/render-submenu-icon.php`).
+ *
+ * @param {BlockConfig} config - Block configuration from `COPY_CONFIG.blocks`.
+ */
+function copyBlockPhp( config ) {
+	const blocksDest = path.join( wpIncludesDir, config.destination );
+
+	for ( const source of config.sources ) {
+		const scriptsSrc = path.join( gutenbergBuildDir, source.scripts );
+		const phpSrc = path.join( gutenbergBuildDir, source.php );
+		const blocks = getStableBlocks( scriptsSrc );
+
+		for ( const blockName of blocks ) {
+			// Top-level <block>.php (dynamic block file).
+			const topLevelPhpSrc = path.join( phpSrc, `${ blockName }.php` );
+			const topLevelPhpDest = path.join( blocksDest, `${ blockName }.php` );
+			if ( fs.existsSync( topLevelPhpSrc ) ) {
+				fs.mkdirSync( blocksDest, { recursive: true } );
+				fs.copyFileSync( topLevelPhpSrc, topLevelPhpDest );
 			}
 
-			// 4. Copy PHP subdirectories from build (e.g., navigation-link/shared/*.php)
+			// Nested PHP helpers under <block>/, excluding the block's own index.php.
 			const blockPhpDir = path.join( phpSrc, blockName );
 			if ( fs.existsSync( blockPhpDir ) ) {
+				const blockDest = path.join( blocksDest, blockName );
 				const rootIndex = path.join( blockPhpDir, 'index.php' );
+
+				/**
+				 * @param {string} src
+				 * @return {boolean}
+				 */
+				function hasPhpFiles( src ) {
+					const stat = fs.statSync( src );
+					if ( stat.isDirectory() ) {
+						return fs.readdirSync( src, { withFileTypes: true } ).some(
+							( entry ) => hasPhpFiles( path.join( src, entry.name ) )
+						);
+					}
+					return src.endsWith( '.php' ) && src !== rootIndex;
+				}
+
 				fs.cpSync( blockPhpDir, blockDest, {
 					recursive: true,
-					filter: function hasPhpFiles( src ) {
-						const stat = fs.statSync( src );
-						if ( stat.isDirectory() ) {
-							return fs.readdirSync( src, { withFileTypes: true } ).some(
-								( entry ) => hasPhpFiles( path.join( src, entry.name ) )
-							);
-						}
-						// Copy PHP files, but skip root index.php (handled by step 3).
-						return src.endsWith( '.php' ) && src !== rootIndex;
-					},
+					filter: hasPhpFiles,
 				} );
 			}
 		}
 
 		console.log(
-			`   ✅ ${ source.name } blocks copied (${ blockDirs.length } blocks)`
+			`   ✅ ${ source.name } block PHP copied (${ blocks.length } blocks)`
+		);
+	}
+}
+
+/**
+ * Copy per-block CSS files for every stable block.
+ *
+ * @param {BlockConfig} config - Block configuration from `COPY_CONFIG.blocks`.
+ */
+function copyBlockStyles( config ) {
+	const blocksDest = path.join( wpIncludesDir, config.destination );
+
+	for ( const source of config.sources ) {
+		const scriptsSrc = path.join( gutenbergBuildDir, source.scripts );
+		const stylesSrc = path.join( gutenbergBuildDir, source.styles );
+		const blocks = getStableBlocks( scriptsSrc );
+
+		let stylesCopied = 0;
+		for ( const blockName of blocks ) {
+			const blockStylesSrc = path.join( stylesSrc, blockName );
+			if ( ! fs.existsSync( blockStylesSrc ) ) {
+				continue;
+			}
+
+			const blockDest = path.join( blocksDest, blockName );
+			fs.mkdirSync( blockDest, { recursive: true } );
+
+			const cssFiles = fs
+				.readdirSync( blockStylesSrc )
+				.filter( ( file ) => file.endsWith( '.css' ) );
+			for ( const cssFile of cssFiles ) {
+				fs.copyFileSync(
+					path.join( blockStylesSrc, cssFile ),
+					path.join( blockDest, cssFile )
+				);
+			}
+			if ( cssFiles.length > 0 ) {
+				stylesCopied++;
+			}
+		}
+
+		console.log(
+			`   ✅ ${ source.name } block CSS copied (${ stylesCopied } blocks)`
 		);
 	}
 }
@@ -218,6 +385,7 @@ function copyBlockAssets( config ) {
  */
 function generateScriptModulesPackages() {
 	const modulesDir = path.join( gutenbergBuildDir, 'modules' );
+	/** @type {Record<string, any>} */
 	const assets = {};
 
 	/**
@@ -254,7 +422,7 @@ function generateScriptModulesPackages() {
 				} catch ( error ) {
 					console.error(
 						`   ⚠️  Error reading ${ relativePath }:`,
-						error.message
+						error instanceof Error ? error.message : String( error )
 					);
 				}
 			}
@@ -291,6 +459,7 @@ function generateScriptModulesPackages() {
  */
 function generateScriptLoaderPackages() {
 	const scriptsDir = path.join( gutenbergBuildDir, 'scripts' );
+	/** @type {Record<string, any>} */
 	const assets = {};
 
 	if ( ! fs.existsSync( scriptsDir ) ) {
@@ -326,7 +495,7 @@ function generateScriptLoaderPackages() {
 		} catch ( error ) {
 			console.error(
 				`   ⚠️  Error reading ${ entry.name }/index.min.asset.php:`,
-				error.message
+				error instanceof Error ? error.message : String( error )
 			);
 		}
 	}
@@ -354,9 +523,10 @@ function generateScriptLoaderPackages() {
 }
 
 /**
- * Generate require-dynamic-blocks.php and require-static-blocks.php.
- * Reads all block.json files from wp-includes/blocks and categorizes them.
- * Only includes blocks from block-library, not widgets.
+ * Generate `require-*-blocks.php` files.
+ *
+ * Reads all `block.json` files from the block-library (widgets are ignored) and
+ * creates `require-dynamic-blocks.php` and `require-static-blocks.php` files.
  */
 function generateBlockRegistrationFiles() {
 	const blocksDir = path.join( wpIncludesDir, 'blocks' );
@@ -447,12 +617,15 @@ ${ staticBlocks.map( ( name ) => `\t'${ name }',` ).join( '\n' ) }
 }
 
 /**
- * Generate blocks-json.php from all block.json files.
- * Reads all block.json files and combines them into a single PHP array.
- * Uses json2php to maintain consistency with Core's formatting.
+ * Generate a `blocks-json.php` file.
+ *
+ * Reads all `block.json` files and combines them into a single PHP array.
+ *
+ * This must run after `copyBlockJson` has populated `wp-includes/blocks/`.
  */
 function generateBlocksJson() {
 	const blocksDir = path.join( wpIncludesDir, 'blocks' );
+	/** @type {Record<string, any>} */
 	const blocks = {};
 
 	if ( ! fs.existsSync( blocksDir ) ) {
@@ -478,7 +651,7 @@ function generateBlocksJson() {
 			} catch ( error ) {
 				console.error(
 					`   ⚠️  Error reading ${ entry.name }/block.json:`,
-					error.message
+					error instanceof Error ? error.message : String( error )
 				);
 			}
 		}
@@ -508,7 +681,7 @@ function generateBlocksJson() {
  * Main execution function.
  */
 async function main() {
-	console.log( `📦 Copying Gutenberg build to ${ buildTarget }/...` );
+	console.log( '📦 Copying Gutenberg build to src/...' );
 
 	if ( ! fs.existsSync( gutenbergBuildDir ) ) {
 		console.error( '❌ Gutenberg build directory not found' );
@@ -518,95 +691,18 @@ async function main() {
 
 	// 1. Copy JavaScript packages.
 	console.log( '\n📦 Copying JavaScript packages...' );
-	const scriptsConfig = COPY_CONFIG.scripts;
-	const scriptsSrc = path.join( gutenbergBuildDir, scriptsConfig.source );
-	const scriptsDest = path.join( wpIncludesDir, scriptsConfig.destination );
+	copyScripts( COPY_CONFIG.scripts );
 
-	if ( fs.existsSync( scriptsSrc ) ) {
-		const entries = fs.readdirSync( scriptsSrc, { withFileTypes: true } );
+	console.log( '\n📦 Copying block.json files...' );
+	copyBlockJson( COPY_CONFIG.blocks );
 
-		for ( const entry of entries ) {
-			const src = path.join( scriptsSrc, entry.name );
-
-			if ( entry.isDirectory() ) {
-				// Check if this should be copied as a directory (like vendors/).
-				if (
-					scriptsConfig.copyDirectories &&
-					scriptsConfig.directoryRenames &&
-					scriptsConfig.directoryRenames[ entry.name ]
-				) {
-					/*
-					 * Copy special directories with rename (vendors/ → vendor/).
-					 * Only copy react-jsx-runtime from vendors (react and react-dom come from Core's node_modules).
-					 */
-					const destName =
-						scriptsConfig.directoryRenames[ entry.name ];
-					const dest = path.join( scriptsDest, destName );
-
-					if ( entry.name === 'vendors' ) {
-						// Only copy react-jsx-runtime files, skip react and react-dom.
-						const vendorFiles = fs.readdirSync( src );
-						let copiedCount = 0;
-						fs.mkdirSync( dest, { recursive: true } );
-						for ( const file of vendorFiles ) {
-							if (
-								file.startsWith( 'react-jsx-runtime' ) &&
-								file.endsWith( '.js' )
-							) {
-								const srcFile = path.join( src, file );
-								const destFile = path.join( dest, file );
-
-								fs.copyFileSync( srcFile, destFile );
-								copiedCount++;
-							}
-						}
-						console.log(
-							`   ✅ ${ entry.name }/ → ${ destName }/ (react-jsx-runtime only, ${ copiedCount } files)`
-						);
-					}
-				} else {
-					/*
-					 * Flatten package structure: package-name/index.js → package-name.js.
-					 * This matches Core's expected file structure.
-					 */
-					const packageFiles = fs.readdirSync( src );
-
-					for ( const file of packageFiles ) {
-						if (
-							/^index\.(js|min\.js)$/.test( file )
-						) {
-							const srcFile = path.join( src, file );
-							// Replace 'index.' with 'package-name.'.
-							const destFile = file.replace(
-								/^index\./,
-								`${ entry.name }.`
-							);
-							const destPath = path.join( scriptsDest, destFile );
-
-							fs.mkdirSync( path.dirname( destPath ), {
-								recursive: true,
-							} );
-
-							fs.copyFileSync( srcFile, destPath );
-						}
-					}
-				}
-			} else if ( entry.isFile() && entry.name.endsWith( '.js' ) ) {
-				// Copy root-level JS files.
-				const dest = path.join( scriptsDest, entry.name );
-				fs.mkdirSync( path.dirname( dest ), { recursive: true } );
-				fs.copyFileSync( src, dest );
-			}
-		}
-
-		console.log( '   ✅ JavaScript packages copied' );
-	}
+	console.log( '\n📦 Copying block PHP files...' );
+	copyBlockPhp( COPY_CONFIG.blocks );
 
-	// 2. Copy blocks (unified: scripts, styles, PHP, JSON).
-	console.log( '\n📦 Copying blocks...' );
-	copyBlockAssets( COPY_CONFIG.blocks );
+	console.log( '\n📦 Copying block CSS files...' );
+	copyBlockStyles( COPY_CONFIG.blocks );
 
-	// 3. Generate script-modules-packages.php from individual asset files.
+	// 3. Generate script-modules-packages.php.
 	console.log( '\n📦 Generating script-modules-packages.php...' );
 	generateScriptModulesPackages();
 
diff --git a/tools/gutenberg/utils.js b/tools/gutenberg/utils.js
index 43047b5ee5dd7..3ba95199578b4 100644
--- a/tools/gutenberg/utils.js
+++ b/tools/gutenberg/utils.js
@@ -139,7 +139,7 @@ async function resolveExpectedSha( { ref, ghcrRepo, isMutable } ) {
 
 /**
  * Trigger a fresh download of the Gutenberg artifact by spawning download.js,
- * then run `grunt build:gutenberg --dev` to copy the build to src/.
+ * then run `grunt build:gutenberg` to copy the build into src/.
  * Exits the process if either step fails.
  */
 function downloadGutenberg() {
@@ -148,7 +148,7 @@ function downloadGutenberg() {
 		process.exit( downloadResult.status ?? 1 );
 	}
 
-	const buildResult = spawnSync( 'grunt', [ 'build:gutenberg', '--dev' ], { stdio: 'inherit', shell: true } );
+	const buildResult = spawnSync( 'grunt', [ 'build:gutenberg' ], { stdio: 'inherit', shell: true } );
 	if ( buildResult.status !== 0 ) {
 		process.exit( buildResult.status ?? 1 );
 	}
diff --git a/tsconfig.json b/tsconfig.json
index 87abe9fb7a42b..e9f36c374ac89 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -30,6 +30,7 @@
 		"src/js/_enqueues/wp/code-editor.js",
 		"src/js/_enqueues/lib/codemirror/javascript-lint.js",
 		"src/js/_enqueues/lib/codemirror/htmlhint-kses.js",
+		"tools/gutenberg/copy.js",
 		"tools/gutenberg/download.js",
 		"tools/gutenberg/utils.js"
 	]