diff --git a/.gitignore b/.gitignore
index 10986068e31..15d176078e6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -24,6 +24,7 @@ packages/blockly/tests/compile/main_compressed.js
 packages/blockly/tests/compile/main_compressed.js.map
 packages/blockly/tests/mocha/test-modules.generated.mjs
 packages/blockly/temp/
+packages/blockly/_deploy
 
 # Docs:
 # Autogenerated reference docs, do not check in
diff --git a/eslint.config.mjs b/eslint.config.mjs
index f721f993b94..f7188ef9eba 100644
--- a/eslint.config.mjs
+++ b/eslint.config.mjs
@@ -144,11 +144,6 @@ export default defineConfig(
   {
     // Note: there should be no other properties in this object
     ignores: [
-      // All Packages
-      'packages/*/node_modules/**',
-      'packages/**/build/',
-      'packages/**/dist/',
-      // Core Build artifacts
       // All Packages
       'packages/*/node_modules/**',
       'packages/**/build/',
@@ -157,6 +152,7 @@ export default defineConfig(
       'packages/blockly/msg/*',
       'packages/blockly/typings/*',
       'packages/blockly/docs/*',
+      'packages/blockly/_deploy/*',
       // Core Tests other than mocha unit tests
       'packages/blockly/tests/blocks/*',
       'packages/blockly/tests/themes/*',
diff --git a/nx.json b/nx.json
index d609231eb9e..d227e673a03 100644
--- a/nx.json
+++ b/nx.json
@@ -37,16 +37,12 @@
       "outputs": ["{projectRoot}/build/msg"],
       "cache": true
     },
-    "minify": {
-      "outputs": ["{projectRoot}/dist"],
-      "cache": true
-    },
     "package": {
       "outputs": ["{projectRoot}/dist", "{projectRoot}/build"],
       "cache": true
     },
     "prepareDemos": {
-      "outputs": ["{projectRoot}/../_deploy"],
+      "outputs": ["{projectRoot}/_deploy"],
       "cache": true
     },
     "tsc": {
diff --git a/package-lock.json b/package-lock.json
index 44e6017f8bb..1498fc0d710 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -7650,99 +7650,6 @@
         "@shikijs/vscode-textmate": "^10.0.2"
       }
     },
-    "node_modules/@gulp-sourcemaps/identity-map": {
-      "version": "2.0.1",
-      "resolved": "https://registry.npmjs.org/@gulp-sourcemaps/identity-map/-/identity-map-2.0.1.tgz",
-      "integrity": "sha512-Tb+nSISZku+eQ4X1lAkevcQa+jknn/OVUgZ3XCxEKIsLsqYuPoJwJOPQeaOk75X3WPftb29GWY1eqE7GLsXb1Q==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "acorn": "^6.4.1",
-        "normalize-path": "^3.0.0",
-        "postcss": "^7.0.16",
-        "source-map": "^0.6.0",
-        "through2": "^3.0.1"
-      },
-      "engines": {
-        "node": ">= 0.10"
-      }
-    },
-    "node_modules/@gulp-sourcemaps/identity-map/node_modules/acorn": {
-      "version": "6.4.2",
-      "resolved": "https://registry.npmjs.org/acorn/-/acorn-6.4.2.tgz",
-      "integrity": "sha512-XtGIhXwF8YM8bJhGxG5kXgjkEuNGLTkoYqVE+KMR+aspr4KGYmKYg7yUe3KghyQ9yheNwLnjmzh/7+gfDBmHCQ==",
-      "dev": true,
-      "license": "MIT",
-      "bin": {
-        "acorn": "bin/acorn"
-      },
-      "engines": {
-        "node": ">=0.4.0"
-      }
-    },
-    "node_modules/@gulp-sourcemaps/identity-map/node_modules/picocolors": {
-      "version": "0.2.1",
-      "resolved": "https://registry.npmjs.org/picocolors/-/picocolors-0.2.1.tgz",
-      "integrity": "sha512-cMlDqaLEqfSaW8Z7N5Jw+lyIW869EzT73/F5lhtY9cLGoVxSXznfgfXMO0Z5K0o0Q2TkTXq+0KFsdnSe3jDViA==",
-      "dev": true,
-      "license": "ISC"
-    },
-    "node_modules/@gulp-sourcemaps/identity-map/node_modules/postcss": {
-      "version": "7.0.39",
-      "resolved": "https://registry.npmjs.org/postcss/-/postcss-7.0.39.tgz",
-      "integrity": "sha512-yioayjNbHn6z1/Bywyb2Y4s3yvDAeXGOyxqD+LnVOinq6Mdmd++SW2wUNVzavyyHxd6+DxzWGIuosg6P1Rj8uA==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "picocolors": "^0.2.1",
-        "source-map": "^0.6.1"
-      },
-      "engines": {
-        "node": ">=6.0.0"
-      },
-      "funding": {
-        "type": "opencollective",
-        "url": "https://opencollective.com/postcss/"
-      }
-    },
-    "node_modules/@gulp-sourcemaps/identity-map/node_modules/through2": {
-      "version": "3.0.2",
-      "resolved": "https://registry.npmjs.org/through2/-/through2-3.0.2.tgz",
-      "integrity": "sha512-enaDQ4MUyP2W6ZyT6EsMzqBPZaM/avg8iuo+l2d3QCs0J+6RaqkHV/2/lOwDTueBHeJ/2LG9lrLW3d5rWPucuQ==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "inherits": "^2.0.4",
-        "readable-stream": "2 || 3"
-      }
-    },
-    "node_modules/@gulp-sourcemaps/map-sources": {
-      "version": "1.0.0",
-      "resolved": "https://registry.npmjs.org/@gulp-sourcemaps/map-sources/-/map-sources-1.0.0.tgz",
-      "integrity": "sha512-o/EatdaGt8+x2qpb0vFLC/2Gug/xYPRXb6a+ET1wGYKozKN3krDWC/zZFZAtrzxJHuDL12mwdfEFKcKMNvc55A==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "normalize-path": "^2.0.1",
-        "through2": "^2.0.3"
-      },
-      "engines": {
-        "node": ">= 0.10"
-      }
-    },
-    "node_modules/@gulp-sourcemaps/map-sources/node_modules/normalize-path": {
-      "version": "2.1.1",
-      "resolved": "https://registry.npmjs.org/normalize-path/-/normalize-path-2.1.1.tgz",
-      "integrity": "sha512-3pKJwH184Xo/lnH6oyP1q2pMd7HcypqqmRs91/6/i2CGtWwIKGCkOOMTm/zXbgTEWHw1uNpNi/igc3ePOYHb6w==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "remove-trailing-separator": "^1.0.1"
-      },
-      "engines": {
-        "node": ">=0.10.0"
-      }
-    },
     "node_modules/@gulpjs/messages": {
       "version": "1.1.0",
       "resolved": "https://registry.npmjs.org/@gulpjs/messages/-/messages-1.1.0.tgz",
@@ -12491,13 +12398,6 @@
         "@types/estree": "*"
       }
     },
-    "node_modules/@types/expect": {
-      "version": "1.20.4",
-      "resolved": "https://registry.npmjs.org/@types/expect/-/expect-1.20.4.tgz",
-      "integrity": "sha512-Q5Vn3yjTDyCMV50TB6VRIbQNxSE4OmZR86VSbGaNpfUolm0iePBB4KdEEHmxoY5sT2+2DIvXW0rvMDP2nHZ4Mg==",
-      "dev": true,
-      "license": "MIT"
-    },
     "node_modules/@types/express": {
       "version": "5.0.6",
       "resolved": "https://registry.npmjs.org/@types/express/-/express-5.0.6.tgz",
@@ -12805,17 +12705,6 @@
       "integrity": "sha512-ko/gIFJRv177XgZsZcBwnqJN5x/Gien8qNOn0D5bQU/zAzVf9Zt3BlcUiLqhV9y4ARk0GbT3tnUiPNgnTXzc/Q==",
       "license": "MIT"
     },
-    "node_modules/@types/vinyl": {
-      "version": "2.0.12",
-      "resolved": "https://registry.npmjs.org/@types/vinyl/-/vinyl-2.0.12.tgz",
-      "integrity": "sha512-Sr2fYMBUVGYq8kj3UthXFAu5UN6ZW+rYr4NACjZQJvHvj+c8lYv0CahmZ2P/r7iUkN44gGUBwqxZkrKXYPb7cw==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "@types/expect": "^1.20.4",
-        "@types/node": "*"
-      }
-    },
     "node_modules/@types/which": {
       "version": "2.0.2",
       "resolved": "https://registry.npmjs.org/@types/which/-/which-2.0.2.tgz",
@@ -14208,19 +14097,6 @@
       "dev": true,
       "license": "MIT"
     },
-    "node_modules/atob": {
-      "version": "2.1.2",
-      "resolved": "https://registry.npmjs.org/atob/-/atob-2.1.2.tgz",
-      "integrity": "sha512-Wm6ukoaOGJi/73p/cl2GvLjTI5JM1k/O14isD73YML8StrH/7/lRFgmg8nICZgD3bZZvjwCGxtMOD3wWNAu8cg==",
-      "dev": true,
-      "license": "(MIT OR Apache-2.0)",
-      "bin": {
-        "atob": "bin/atob.js"
-      },
-      "engines": {
-        "node": ">= 4.5.0"
-      }
-    },
     "node_modules/autoprefixer": {
       "version": "10.5.4",
       "resolved": "https://registry.npmjs.org/autoprefixer/-/autoprefixer-10.5.4.tgz",
@@ -14738,19 +14614,6 @@
         "url": "https://github.com/sponsors/sindresorhus"
       }
     },
-    "node_modules/binaryextensions": {
-      "version": "2.3.0",
-      "resolved": "https://registry.npmjs.org/binaryextensions/-/binaryextensions-2.3.0.tgz",
-      "integrity": "sha512-nAihlQsYGyc5Bwq6+EsubvANYGExeJKHDO3RjnvwU042fawQTQfM3Kxn7IHUXQOz4bzfwsGYYHGSvXyW4zOGLg==",
-      "dev": true,
-      "license": "MIT",
-      "engines": {
-        "node": ">=0.8"
-      },
-      "funding": {
-        "url": "https://bevry.me/fund"
-      }
-    },
     "node_modules/bl": {
       "version": "4.1.0",
       "resolved": "https://registry.npmjs.org/bl/-/bl-4.1.0.tgz",
@@ -16703,18 +16566,6 @@
         "url": "https://github.com/sponsors/sindresorhus"
       }
     },
-    "node_modules/css": {
-      "version": "3.0.0",
-      "resolved": "https://registry.npmjs.org/css/-/css-3.0.0.tgz",
-      "integrity": "sha512-DG9pFfwOrzc+hawpmqX/dHYHJG+Bsdb0klhyi1sDneOgGOXy9wQIC8hzyVp1e4NRYDBdxcylvywPkkXCHAzTyQ==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "inherits": "^2.0.4",
-        "source-map": "^0.6.1",
-        "source-map-resolve": "^0.6.0"
-      }
-    },
     "node_modules/css-blank-pseudo": {
       "version": "7.0.1",
       "resolved": "https://registry.npmjs.org/css-blank-pseudo/-/css-blank-pseudo-7.0.1.tgz",
@@ -17160,20 +17011,6 @@
       "integrity": "sha512-z1HGKcYy2xA8AGQfwrn0PAy+PB7X/GSj3UVJW9qKyn43xWa+gl5nXmU4qqLMRzWVLFC8KusUX8T/0kCiOYpAIQ==",
       "license": "MIT"
     },
-    "node_modules/d": {
-      "version": "1.0.2",
-      "resolved": "https://registry.npmjs.org/d/-/d-1.0.2.tgz",
-      "integrity": "sha512-MOqHvMWF9/9MX6nza0KgvFH4HpMU0EF5uUDXqX/BtxtU8NfB0QzRtJ8Oe/6SuS4kbhyzVJwjd97EA4PKrzJ8bw==",
-      "dev": true,
-      "license": "ISC",
-      "dependencies": {
-        "es5-ext": "^0.10.64",
-        "type": "^2.7.2"
-      },
-      "engines": {
-        "node": ">=0.12"
-      }
-    },
     "node_modules/dat.gui": {
       "version": "0.7.9",
       "resolved": "https://registry.npmjs.org/dat.gui/-/dat.gui-0.7.9.tgz",
@@ -17241,28 +17078,6 @@
         }
       }
     },
-    "node_modules/debug-fabulous": {
-      "version": "1.1.0",
-      "resolved": "https://registry.npmjs.org/debug-fabulous/-/debug-fabulous-1.1.0.tgz",
-      "integrity": "sha512-GZqvGIgKNlUnHUPQhepnUZFIMoi3dgZKQBzKDeL2g7oJF9SNAji/AAu36dusFUas0O+pae74lNeoIPHqXWDkLg==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "debug": "3.X",
-        "memoizee": "0.4.X",
-        "object-assign": "4.X"
-      }
-    },
-    "node_modules/debug-fabulous/node_modules/debug": {
-      "version": "3.2.7",
-      "resolved": "https://registry.npmjs.org/debug/-/debug-3.2.7.tgz",
-      "integrity": "sha512-CFjzYYAi4ThfiQvizrFQevTTXHtnCqWfe7x1AhgEscTz6ZbLbfoLRLPugTQyBth6f8ZERVUSyWHFD/7Wu4t1XQ==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "ms": "^2.1.1"
-      }
-    },
     "node_modules/decamelize": {
       "version": "6.0.1",
       "resolved": "https://registry.npmjs.org/decamelize/-/decamelize-6.0.1.tgz",
@@ -17296,16 +17111,6 @@
         "url": "https://github.com/sponsors/wooorm"
       }
     },
-    "node_modules/decode-uri-component": {
-      "version": "0.2.2",
-      "resolved": "https://registry.npmjs.org/decode-uri-component/-/decode-uri-component-0.2.2.tgz",
-      "integrity": "sha512-FqUYQ+8o158GyGTrMFJms9qh3CqTKvAqgqsTnkLI8sKu0028orqBhxNMFkFen0zGyg6epACD32pjVk58ngIErQ==",
-      "dev": true,
-      "license": "MIT",
-      "engines": {
-        "node": ">=0.10"
-      }
-    },
     "node_modules/decompress-response": {
       "version": "6.0.0",
       "resolved": "https://registry.npmjs.org/decompress-response/-/decompress-response-6.0.0.tgz",
@@ -17562,16 +17367,6 @@
         "node": ">=8"
       }
     },
-    "node_modules/detect-newline": {
-      "version": "2.1.0",
-      "resolved": "https://registry.npmjs.org/detect-newline/-/detect-newline-2.1.0.tgz",
-      "integrity": "sha512-CwffZFvlJffUg9zZA0uqrjQayUTC8ob94pnr5sFwaVv3IOmkfUHcWH+jXaQK3askE51Cqe8/9Ql/0uXNwqZ8Zg==",
-      "dev": true,
-      "license": "MIT",
-      "engines": {
-        "node": ">=0.10.0"
-      }
-    },
     "node_modules/detect-node": {
       "version": "2.1.0",
       "resolved": "https://registry.npmjs.org/detect-node/-/detect-node-2.1.0.tgz",
@@ -18108,62 +17903,6 @@
         "tests/browser-compat"
       ]
     },
-    "node_modules/es5-ext": {
-      "version": "0.10.64",
-      "resolved": "https://registry.npmjs.org/es5-ext/-/es5-ext-0.10.64.tgz",
-      "integrity": "sha512-p2snDhiLaXe6dahss1LddxqEm+SkuDvV8dnIQG0MWjyHpcMNfXKPE+/Cc0y+PhxJX3A4xGNeFCj5oc0BUh6deg==",
-      "dev": true,
-      "hasInstallScript": true,
-      "license": "ISC",
-      "dependencies": {
-        "es6-iterator": "^2.0.3",
-        "es6-symbol": "^3.1.3",
-        "esniff": "^2.0.1",
-        "next-tick": "^1.1.0"
-      },
-      "engines": {
-        "node": ">=0.10"
-      }
-    },
-    "node_modules/es6-iterator": {
-      "version": "2.0.3",
-      "resolved": "https://registry.npmjs.org/es6-iterator/-/es6-iterator-2.0.3.tgz",
-      "integrity": "sha512-zw4SRzoUkd+cl+ZoE15A9o1oQd920Bb0iOJMQkQhl3jNc03YqVjAhG7scf9C5KWRU/R13Orf588uCC6525o02g==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "d": "1",
-        "es5-ext": "^0.10.35",
-        "es6-symbol": "^3.1.1"
-      }
-    },
-    "node_modules/es6-symbol": {
-      "version": "3.1.4",
-      "resolved": "https://registry.npmjs.org/es6-symbol/-/es6-symbol-3.1.4.tgz",
-      "integrity": "sha512-U9bFFjX8tFiATgtkJ1zg25+KviIXpgRvRHS8sau3GfhVzThRQrOeksPeT0BWW2MNZs1OEWJ1DPXOQMn0KKRkvg==",
-      "dev": true,
-      "license": "ISC",
-      "dependencies": {
-        "d": "^1.0.2",
-        "ext": "^1.7.0"
-      },
-      "engines": {
-        "node": ">=0.12"
-      }
-    },
-    "node_modules/es6-weak-map": {
-      "version": "2.0.3",
-      "resolved": "https://registry.npmjs.org/es6-weak-map/-/es6-weak-map-2.0.3.tgz",
-      "integrity": "sha512-p5um32HOTO1kP+w7PRnB+5lQ43Z6muuMuIMffvDN8ZB4GcnjLBV6zGStpbASIMk4DCAvEaamhe2zhyCb/QXXsA==",
-      "dev": true,
-      "license": "ISC",
-      "dependencies": {
-        "d": "1",
-        "es5-ext": "^0.10.46",
-        "es6-iterator": "^2.0.3",
-        "es6-symbol": "^3.1.1"
-      }
-    },
     "node_modules/esast-util-from-estree": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/esast-util-from-estree/-/esast-util-from-estree-2.0.0.tgz",
@@ -18649,22 +18388,6 @@
       "dev": true,
       "license": "MIT"
     },
-    "node_modules/esniff": {
-      "version": "2.0.1",
-      "resolved": "https://registry.npmjs.org/esniff/-/esniff-2.0.1.tgz",
-      "integrity": "sha512-kTUIGKQ/mDPFoJ0oVfcmyJn4iBDRptjNVIzwIFR7tqWXdVI9xfA2RMwY/gbSpJG3lkdWNEjLap/NqVHZiJsdfg==",
-      "dev": true,
-      "license": "ISC",
-      "dependencies": {
-        "d": "^1.0.1",
-        "es5-ext": "^0.10.62",
-        "event-emitter": "^0.3.5",
-        "type": "^2.7.2"
-      },
-      "engines": {
-        "node": ">=0.10"
-      }
-    },
     "node_modules/espree": {
       "version": "11.2.0",
       "resolved": "https://registry.npmjs.org/espree/-/espree-11.2.0.tgz",
@@ -18887,17 +18610,6 @@
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     },
-    "node_modules/event-emitter": {
-      "version": "0.3.5",
-      "resolved": "https://registry.npmjs.org/event-emitter/-/event-emitter-0.3.5.tgz",
-      "integrity": "sha512-D9rRn9y7kLPnJ+hMq7S/nhvoKwwvVJahBi2BPmx3bvbsEdK3W9ii8cBSGjP+72/LnM4n6fo3+dkCX5FeTQruXA==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "d": "1",
-        "es5-ext": "~0.10.14"
-      }
-    },
     "node_modules/event-target-shim": {
       "version": "5.0.1",
       "resolved": "https://registry.npmjs.org/event-target-shim/-/event-target-shim-5.0.1.tgz",
@@ -19202,16 +18914,6 @@
         "node": ">= 0.6"
       }
     },
-    "node_modules/ext": {
-      "version": "1.7.0",
-      "resolved": "https://registry.npmjs.org/ext/-/ext-1.7.0.tgz",
-      "integrity": "sha512-6hxeJYaL110a9b5TEJSj0gojyHQAmA2ch5Os+ySCiA1QGdS697XWY1pzsrSjqA9LDEEgdB/KypIlR59RcLuHYw==",
-      "dev": true,
-      "license": "ISC",
-      "dependencies": {
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     "node_modules/extend": {
       "version": "3.0.2",
       "resolved": "https://registry.npmjs.org/extend/-/extend-3.0.2.tgz",
@@ -20862,76 +20564,6 @@
         "node": ">=10"
       }
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-    "node_modules/gulp-rename": {
-      "version": "2.1.0",
-      "resolved": "https://registry.npmjs.org/gulp-rename/-/gulp-rename-2.1.0.tgz",
-      "integrity": "sha512-dGuzuH8jQGqCMqC544IEPhs5+O2l+IkdoSZsgd4kY97M1CxQeI3qrmweQBIrxLBbjbe/8uEWK8HHcNBc3OCy4g==",
-      "dev": true,
-      "license": "MIT",
-      "engines": {
-        "node": ">=4"
-      }
-    },
-    "node_modules/gulp-replace": {
-      "version": "1.1.4",
-      "resolved": "https://registry.npmjs.org/gulp-replace/-/gulp-replace-1.1.4.tgz",
-      "integrity": "sha512-SVSF7ikuWKhpAW4l4wapAqPPSToJoiNKsbDoUnRrSgwZHH7lH8pbPeQj1aOVYQrbZKhfSVBxVW+Py7vtulRktw==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "@types/node": "*",
-        "@types/vinyl": "^2.0.4",
-        "istextorbinary": "^3.0.0",
-        "replacestream": "^4.0.3",
-        "yargs-parser": ">=5.0.0-security.0"
-      },
-      "engines": {
-        "node": ">=10"
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-    },
-    "node_modules/gulp-sourcemaps": {
-      "version": "3.0.0",
-      "resolved": "https://registry.npmjs.org/gulp-sourcemaps/-/gulp-sourcemaps-3.0.0.tgz",
-      "integrity": "sha512-RqvUckJkuYqy4VaIH60RMal4ZtG0IbQ6PXMNkNsshEGJ9cldUPRb/YCgboYae+CLAs1HQNb4ADTKCx65HInquQ==",
-      "dev": true,
-      "license": "ISC",
-      "dependencies": {
-        "@gulp-sourcemaps/identity-map": "^2.0.1",
-        "@gulp-sourcemaps/map-sources": "^1.0.0",
-        "acorn": "^6.4.1",
-        "convert-source-map": "^1.0.0",
-        "css": "^3.0.0",
-        "debug-fabulous": "^1.0.0",
-        "detect-newline": "^2.0.0",
-        "graceful-fs": "^4.0.0",
-        "source-map": "^0.6.0",
-        "strip-bom-string": "^1.0.0",
-        "through2": "^2.0.0"
-      },
-      "engines": {
-        "node": ">= 6"
-      }
-    },
-    "node_modules/gulp-sourcemaps/node_modules/acorn": {
-      "version": "6.4.2",
-      "resolved": "https://registry.npmjs.org/acorn/-/acorn-6.4.2.tgz",
-      "integrity": "sha512-XtGIhXwF8YM8bJhGxG5kXgjkEuNGLTkoYqVE+KMR+aspr4KGYmKYg7yUe3KghyQ9yheNwLnjmzh/7+gfDBmHCQ==",
-      "dev": true,
-      "license": "MIT",
-      "bin": {
-        "acorn": "bin/acorn"
-      },
-      "engines": {
-        "node": ">=0.4.0"
-      }
-    },
-    "node_modules/gulp-sourcemaps/node_modules/convert-source-map": {
-      "version": "1.9.0",
-      "resolved": "https://registry.npmjs.org/convert-source-map/-/convert-source-map-1.9.0.tgz",
-      "integrity": "sha512-ASFBup0Mz1uyiIjANan1jzLQami9z1PoYSZCiiYW2FczPbenXc45FZdBZLzOT+r6+iciuEModtmCti+hjaAk0A==",
-      "dev": true,
-      "license": "MIT"
-    },
     "node_modules/gulplog": {
       "version": "2.2.0",
       "resolved": "https://registry.npmjs.org/gulplog/-/gulplog-2.2.0.tgz",
@@ -22490,23 +22122,6 @@
         "node": ">=0.10.0"
       }
     },
-    "node_modules/istextorbinary": {
-      "version": "3.3.0",
-      "resolved": "https://registry.npmjs.org/istextorbinary/-/istextorbinary-3.3.0.tgz",
-      "integrity": "sha512-Tvq1W6NAcZeJ8op+Hq7tdZ434rqnMx4CCZ7H0ff83uEloDvVbqAwaMTZcafKGJT0VHkYzuXUiCY4hlXQg6WfoQ==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "binaryextensions": "^2.2.0",
-        "textextensions": "^3.2.0"
-      },
-      "engines": {
-        "node": ">=8"
-      },
-      "funding": {
-        "url": "https://bevry.me/fund"
-      }
-    },
     "node_modules/jackspeak": {
       "version": "3.4.3",
       "resolved": "https://registry.npmjs.org/jackspeak/-/jackspeak-3.4.3.tgz",
@@ -23955,16 +23570,6 @@
         "yallist": "^3.0.2"
       }
     },
-    "node_modules/lru-queue": {
-      "version": "0.1.0",
-      "resolved": "https://registry.npmjs.org/lru-queue/-/lru-queue-0.1.0.tgz",
-      "integrity": "sha512-BpdYkt9EvGl8OfWHDQPISVpcl5xZthb+XPsbELj5AQXxIC8IriDZIQYjBJPEm5rS420sjZ0TLEzRcq5KdBhYrQ==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "es5-ext": "~0.10.2"
-      }
-    },
     "node_modules/lunr": {
       "version": "2.3.9",
       "resolved": "https://registry.npmjs.org/lunr/-/lunr-2.3.9.tgz",
@@ -24462,33 +24067,6 @@
         "node": ">= 4.0.0"
       }
     },
-    "node_modules/memoizee": {
-      "version": "0.4.17",
-      "resolved": "https://registry.npmjs.org/memoizee/-/memoizee-0.4.17.tgz",
-      "integrity": "sha512-DGqD7Hjpi/1or4F/aYAspXKNm5Yili0QDAFAY4QYvpqpgiY6+1jOfqpmByzjxbWd/T9mChbCArXAbDAsTm5oXA==",
-      "dev": true,
-      "license": "ISC",
-      "dependencies": {
-        "d": "^1.0.2",
-        "es5-ext": "^0.10.64",
-        "es6-weak-map": "^2.0.3",
-        "event-emitter": "^0.3.5",
-        "is-promise": "^2.2.2",
-        "lru-queue": "^0.1.0",
-        "next-tick": "^1.1.0",
-        "timers-ext": "^0.1.7"
-      },
-      "engines": {
-        "node": ">=0.12"
-      }
-    },
-    "node_modules/memoizee/node_modules/is-promise": {
-      "version": "2.2.2",
-      "resolved": "https://registry.npmjs.org/is-promise/-/is-promise-2.2.2.tgz",
-      "integrity": "sha512-+lP4/6lKUBfQjZ2pdxThZvLUAafmZb8OAxFb8XXtiQmS35INgr85hdOGoEs124ez1FCnZJt6jau/T+alh58QFQ==",
-      "dev": true,
-      "license": "MIT"
-    },
     "node_modules/merge-descriptors": {
       "version": "1.0.3",
       "resolved": "https://registry.npmjs.org/merge-descriptors/-/merge-descriptors-1.0.3.tgz",
@@ -25947,13 +25525,6 @@
         "node": ">= 0.4.0"
       }
     },
-    "node_modules/next-tick": {
-      "version": "1.1.0",
-      "resolved": "https://registry.npmjs.org/next-tick/-/next-tick-1.1.0.tgz",
-      "integrity": "sha512-CXdUiJembsNjuToQvxayPZF9Vqht7hewsvy2sOWafLvi2awflj9mOC6bHIg50orX8IJvWKY9wYQ/zB2kogPslQ==",
-      "dev": true,
-      "license": "ISC"
-    },
     "node_modules/no-case": {
       "version": "3.0.4",
       "resolved": "https://registry.npmjs.org/no-case/-/no-case-3.0.4.tgz",
@@ -30536,68 +30107,6 @@
         "node": ">= 10.13.0"
       }
     },
-    "node_modules/replacestream": {
-      "version": "4.0.3",
-      "resolved": "https://registry.npmjs.org/replacestream/-/replacestream-4.0.3.tgz",
-      "integrity": "sha512-AC0FiLS352pBBiZhd4VXB1Ab/lh0lEgpP+GGvZqbQh8a5cmXVoTe5EX/YeTFArnp4SRGTHh1qCHu9lGs1qG8sA==",
-      "dev": true,
-      "license": "BSD-3-Clause",
-      "dependencies": {
-        "escape-string-regexp": "^1.0.3",
-        "object-assign": "^4.0.1",
-        "readable-stream": "^2.0.2"
-      }
-    },
-    "node_modules/replacestream/node_modules/escape-string-regexp": {
-      "version": "1.0.5",
-      "resolved": "https://registry.npmjs.org/escape-string-regexp/-/escape-string-regexp-1.0.5.tgz",
-      "integrity": "sha512-vbRorB5FUQWvla16U8R/qgaFIya2qGzwDrNmCZuYKrbdSUMG6I1ZCGQRefkRVhuOkIGVne7BQ35DSfo1qvJqFg==",
-      "dev": true,
-      "license": "MIT",
-      "engines": {
-        "node": ">=0.8.0"
-      }
-    },
-    "node_modules/replacestream/node_modules/isarray": {
-      "version": "1.0.0",
-      "resolved": "https://registry.npmjs.org/isarray/-/isarray-1.0.0.tgz",
-      "integrity": "sha512-VLghIWNM6ELQzo7zwmcg0NmTVyWKYjvIeM83yjp0wRDTmUnrM678fQbcKBo6n2CJEF0szoG//ytg+TKla89ALQ==",
-      "dev": true,
-      "license": "MIT"
-    },
-    "node_modules/replacestream/node_modules/readable-stream": {
-      "version": "2.3.8",
-      "resolved": "https://registry.npmjs.org/readable-stream/-/readable-stream-2.3.8.tgz",
-      "integrity": "sha512-8p0AUk4XODgIewSi0l8Epjs+EVnWiK7NoDIEGU0HhE7+ZyY8D1IMY7odu5lRrFXGg71L15KG8QrPmum45RTtdA==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "core-util-is": "~1.0.0",
-        "inherits": "~2.0.3",
-        "isarray": "~1.0.0",
-        "process-nextick-args": "~2.0.0",
-        "safe-buffer": "~5.1.1",
-        "string_decoder": "~1.1.1",
-        "util-deprecate": "~1.0.1"
-      }
-    },
-    "node_modules/replacestream/node_modules/safe-buffer": {
-      "version": "5.1.2",
-      "resolved": "https://registry.npmjs.org/safe-buffer/-/safe-buffer-5.1.2.tgz",
-      "integrity": "sha512-Gd2UZBJDkXlY7GbJxfsE8/nvKkUEU1G38c1siN6QP6a9PT9MmHB8GnpscSmMJSoF8LOIrt8ud/wPtojys4G6+g==",
-      "dev": true,
-      "license": "MIT"
-    },
-    "node_modules/replacestream/node_modules/string_decoder": {
-      "version": "1.1.1",
-      "resolved": "https://registry.npmjs.org/string_decoder/-/string_decoder-1.1.1.tgz",
-      "integrity": "sha512-n/ShnvDi6FHbbVfviro+WojiFzv+s8MPMHBczVePfUpDJLwoLT0ht1l4YwBCbi8pJAveEEdnkHyPyTP/mzRfwg==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "safe-buffer": "~5.1.0"
-      }
-    },
     "node_modules/require-directory": {
       "version": "2.1.1",
       "resolved": "https://registry.npmjs.org/require-directory/-/require-directory-2.1.1.tgz",
@@ -31802,18 +31311,6 @@
         "node": ">=0.10.0"
       }
     },
-    "node_modules/source-map-resolve": {
-      "version": "0.6.0",
-      "resolved": "https://registry.npmjs.org/source-map-resolve/-/source-map-resolve-0.6.0.tgz",
-      "integrity": "sha512-KXBr9d/fO/bWo97NXsPIAW1bFSBOuCnjbNTBMO7N59hsv5i9yzRDfcYwwt0l04+VqnKC+EwzvJZIP/qkuMgR/w==",
-      "deprecated": "See https://github.com/lydell/source-map-resolve#deprecated",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "atob": "^2.1.2",
-        "decode-uri-component": "^0.2.0"
-      }
-    },
     "node_modules/source-map-support": {
       "version": "0.5.19",
       "resolved": "https://registry.npmjs.org/source-map-support/-/source-map-support-0.5.19.tgz",
@@ -32588,19 +32085,6 @@
         "b4a": "^1.6.4"
       }
     },
-    "node_modules/textextensions": {
-      "version": "3.3.0",
-      "resolved": "https://registry.npmjs.org/textextensions/-/textextensions-3.3.0.tgz",
-      "integrity": "sha512-mk82dS8eRABNbeVJrEiN5/UMSCliINAuz8mkUwH4SwslkNP//gbEzlWNS5au0z5Dpx40SQxzqZevZkn+WYJ9Dw==",
-      "dev": true,
-      "license": "MIT",
-      "engines": {
-        "node": ">=8"
-      },
-      "funding": {
-        "url": "https://bevry.me/fund"
-      }
-    },
     "node_modules/thingies": {
       "version": "2.6.1",
       "resolved": "https://registry.npmjs.org/thingies/-/thingies-2.6.1.tgz",
@@ -32617,77 +32101,12 @@
         "tslib": "^2"
       }
     },
-    "node_modules/through2": {
-      "version": "2.0.5",
-      "resolved": "https://registry.npmjs.org/through2/-/through2-2.0.5.tgz",
-      "integrity": "sha512-/mrRod8xqpA+IHSLyGCQ2s8SPHiCDEeQJSep1jqLYeEUClOFG2Qsh+4FU6G9VeqpZnGW/Su8LQGc4YKni5rYSQ==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "readable-stream": "~2.3.6",
-        "xtend": "~4.0.1"
-      }
-    },
-    "node_modules/through2/node_modules/isarray": {
-      "version": "1.0.0",
-      "resolved": "https://registry.npmjs.org/isarray/-/isarray-1.0.0.tgz",
-      "integrity": "sha512-VLghIWNM6ELQzo7zwmcg0NmTVyWKYjvIeM83yjp0wRDTmUnrM678fQbcKBo6n2CJEF0szoG//ytg+TKla89ALQ==",
-      "dev": true,
-      "license": "MIT"
-    },
-    "node_modules/through2/node_modules/readable-stream": {
-      "version": "2.3.8",
-      "resolved": "https://registry.npmjs.org/readable-stream/-/readable-stream-2.3.8.tgz",
-      "integrity": "sha512-8p0AUk4XODgIewSi0l8Epjs+EVnWiK7NoDIEGU0HhE7+ZyY8D1IMY7odu5lRrFXGg71L15KG8QrPmum45RTtdA==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "core-util-is": "~1.0.0",
-        "inherits": "~2.0.3",
-        "isarray": "~1.0.0",
-        "process-nextick-args": "~2.0.0",
-        "safe-buffer": "~5.1.1",
-        "string_decoder": "~1.1.1",
-        "util-deprecate": "~1.0.1"
-      }
-    },
-    "node_modules/through2/node_modules/safe-buffer": {
-      "version": "5.1.2",
-      "resolved": "https://registry.npmjs.org/safe-buffer/-/safe-buffer-5.1.2.tgz",
-      "integrity": "sha512-Gd2UZBJDkXlY7GbJxfsE8/nvKkUEU1G38c1siN6QP6a9PT9MmHB8GnpscSmMJSoF8LOIrt8ud/wPtojys4G6+g==",
-      "dev": true,
-      "license": "MIT"
-    },
-    "node_modules/through2/node_modules/string_decoder": {
-      "version": "1.1.1",
-      "resolved": "https://registry.npmjs.org/string_decoder/-/string_decoder-1.1.1.tgz",
-      "integrity": "sha512-n/ShnvDi6FHbbVfviro+WojiFzv+s8MPMHBczVePfUpDJLwoLT0ht1l4YwBCbi8pJAveEEdnkHyPyTP/mzRfwg==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "safe-buffer": "~5.1.0"
-      }
-    },
     "node_modules/thunky": {
       "version": "1.1.0",
       "resolved": "https://registry.npmjs.org/thunky/-/thunky-1.1.0.tgz",
       "integrity": "sha512-eHY7nBftgThBqOyHGVN+l8gF0BucP09fMo0oO/Lb0w1OF80dJv+lDVpXG60WMQvkcxAkNybKsrEIE3ZtKGmPrA==",
       "license": "MIT"
     },
-    "node_modules/timers-ext": {
-      "version": "0.1.8",
-      "resolved": "https://registry.npmjs.org/timers-ext/-/timers-ext-0.1.8.tgz",
-      "integrity": "sha512-wFH7+SEAcKfJpfLPkrgMPvvwnEtj8W4IurvEyrKsDleXnKLCDw71w8jltvfLa8Rm4qQxxT4jmDBYbJG/z7qoww==",
-      "dev": true,
-      "license": "ISC",
-      "dependencies": {
-        "es5-ext": "^0.10.64",
-        "next-tick": "^1.1.0"
-      },
-      "engines": {
-        "node": ">=0.12"
-      }
-    },
     "node_modules/tiny-invariant": {
       "version": "1.3.3",
       "resolved": "https://registry.npmjs.org/tiny-invariant/-/tiny-invariant-1.3.3.tgz",
@@ -33024,13 +32443,6 @@
         "node": "^22.22.2 || ^24.15.0 || >=26.0.0"
       }
     },
-    "node_modules/type": {
-      "version": "2.7.3",
-      "resolved": "https://registry.npmjs.org/type/-/type-2.7.3.tgz",
-      "integrity": "sha512-8j+1QmAbPvLZow5Qpi6NCaN8FB60p/6x8/vfNqOk/hC+HuvFZhL4+WfekuhQLiqFZXOgQdrs3B+XxEmCc6b3FQ==",
-      "dev": true,
-      "license": "ISC"
-    },
     "node_modules/type-check": {
       "version": "0.4.0",
       "resolved": "https://registry.npmjs.org/type-check/-/type-check-0.4.0.tgz",
@@ -35513,16 +34925,6 @@
       "dev": true,
       "license": "MIT"
     },
-    "node_modules/xtend": {
-      "version": "4.0.2",
-      "resolved": "https://registry.npmjs.org/xtend/-/xtend-4.0.2.tgz",
-      "integrity": "sha512-LKYU1iAXJXUgAXn9URjiu+MWhyUXHsvfp7mcuYm9dSUKK0/CjtrUwFAxD82/mCWbtLsGjFIad0wIsod4zrTAEQ==",
-      "dev": true,
-      "license": "MIT",
-      "engines": {
-        "node": ">=0.4"
-      }
-    },
     "node_modules/y18n": {
       "version": "5.0.8",
       "resolved": "https://registry.npmjs.org/y18n/-/y18n-5.0.8.tgz",
@@ -35870,9 +35272,6 @@
         "glob": "^13.0.6",
         "google-closure-compiler": "^20260920.0.0",
         "gulp": "^5.0.1",
-        "gulp-rename": "^2.1.0",
-        "gulp-replace": "^1.1.4",
-        "gulp-sourcemaps": "^3.0.0",
         "http-server": "^14.1.1",
         "jsdom": "30.1.0",
         "json5": "^2.2.3",
diff --git a/packages/blockly/gulpfile.mjs b/packages/blockly/gulpfile.mjs
index d21e4874c82..b6aaf9e5e7a 100644
--- a/packages/blockly/gulpfile.mjs
+++ b/packages/blockly/gulpfile.mjs
@@ -21,14 +21,6 @@ import {
   deployDemosBeta,
   prepareDemos,
 } from './scripts/gulpfiles/appengine_tasks.mjs';
-import {
-  build,
-  buildAdvancedCompilationTest,
-  minify,
-} from './scripts/gulpfiles/build_tasks.mjs';
-
-// Default target if gulp invoked without specifying.
-export default build;
 
 // Main sequence targets.  They already invoke prerequisites.  Listed
 // in typical order of invocation, and strictly listing prerequisites
@@ -36,17 +28,7 @@ export default build;
 //
 // prettier-ignore
 export {
-  minify,
-  build,
   prepareDemos,
   deployDemosBeta,
   deployDemos,
 }
-
-// Manually-invokable targets that also invoke prerequisites where
-// required.
-//
-// prettier-ignore
-export {
-  buildAdvancedCompilationTest,
-}
diff --git a/packages/blockly/package.json b/packages/blockly/package.json
index 2d209dc66b1..817f4c50549 100644
--- a/packages/blockly/package.json
+++ b/packages/blockly/package.json
@@ -72,20 +72,14 @@
       },
       "test-compile-advanced-browser": {
         "dependsOn": [
-          "test-build-compile-advanced"
+          "test-compile-advanced"
         ]
       },
-      "test-build-compile-advanced": {
+      "test-compile-advanced": {
         "dependsOn": [
           "tsc"
         ]
       },
-      "docs": {
-        "dependsOn": [
-          "package",
-          "^build"
-        ]
-      },
       "start": {
         "dependsOn": [
           {
@@ -101,11 +95,11 @@
     }
   },
   "scripts": {
-    "build": "npm run tsc && gulp build && npm run langfiles",
-    "build-debug": "gulp build --verbose --debug",
-    "build-debug-log": "npm run build:debug > build-debug.log 2>&1 && tail -3 build-debug.log",
-    "build-strict": "gulp build --verbose --strict",
-    "build-strict-log": "npm run build:strict > build-debug.log 2>&1 && tail -3 build-debug.log",
+    "build": "npm run tsc && node \"scripts/build.mjs\"",
+    "build-debug": "npm run build -- --verbose --debug",
+    "build-debug-log": "npm run build-debug > build-debug.log 2>&1 && tail -3 build-debug.log",
+    "build-strict": "npm run build -- --verbose --strict",
+    "build-strict-log": "npm run build-strict > build-debug.log 2>&1 && tail -3 build-debug.log",
     "clean": "node \"scripts/clean.mjs\"",
     "deployDemos": "npm ci && gulp deployDemos",
     "deployDemos:beta": "npm ci && gulp deployDemosBeta",
@@ -113,7 +107,6 @@
     "lint": "eslint .",
     "lint-fix": "eslint . --fix",
     "langfiles": "node \"scripts/langfiles.mjs\"",
-    "minify": "gulp minify",
     "package": "node scripts/package.mjs",
     "prepareDemos": "gulp prepareDemos",
     "start": "npm run package && nx run @blockly/dev-tools:build && node \"scripts/prepare_advanced_playground.mjs\" && concurrently -n devtools-watch,blockly-watch,server \"nx watch --projects=@blockly/dev-tools --includeDependencies -- nx run rebuildAdvancedPlayground\" \"nx watch --projects=blockly -- nx run rebuildBlockly\" \"http-server ./ -s -o /tests/playground.html -c-1\"",
@@ -126,8 +119,7 @@
     "test-mocha-typecheck": "tsc -p tests/mocha/tsconfig.json",
     "test-generators": "node \"tests/generators/test_generators.mjs\"",
     "test-mocha-interactive": "npm run build && node scripts/prepare_mocha_bundle.mjs && concurrently -n tsc,tsc:tests,esbuild,python3 \"tsc --watch --preserveWatchOutput --outDir \"build/src\" --declarationDir \"build/declarations\"\" \"npm run test-mocha-typecheck -- --watch --preserveWatchOutput\" \"esbuild build/tests/bundle-entry.js --bundle --sourcemap --alias:blockly/core=./build/src/core/blockly.js --alias:blockly/blocks=./build/src/blocks/blocks.js --alias:blockly=./build/src/core/blockly.js --outfile=build/tests/mocha-bundle.js --servedir=. --serve=127.0.0.1:8080 --watch=forever --log-level=warning\" \"python3 -m webbrowser 'http://localhost:8080/tests/mocha/index.html'\"",
-    "test-build-compile-advanced": "gulp buildAdvancedCompilationTest --debug",
-    "test-compile-advanced": "nx run blockly:test-build-compile-advanced",
+    "test-compile-advanced": "npm run tsc && node \"tests/compile/test_compile_advanced.mjs\" --debug",
     "test-compile-advanced-browser": "node \"tests/compile/webdriver.js\"",
     "test-renamings": "node \"tests/migration/validate-renamings.mjs\"",
     "test-type-definitions": "tsc -p ./tests/typescript/tsconfig.json -outDir \"build/test-types\"",
@@ -199,9 +191,6 @@
     "glob": "^13.0.6",
     "google-closure-compiler": "^20260920.0.0",
     "gulp": "^5.0.1",
-    "gulp-rename": "^2.1.0",
-    "gulp-replace": "^1.1.4",
-    "gulp-sourcemaps": "^3.0.0",
     "http-server": "^14.1.1",
     "jsdom": "30.1.0",
     "json5": "^2.2.3",
diff --git a/packages/blockly/scripts/gulpfiles/build_tasks.mjs b/packages/blockly/scripts/build.mjs
similarity index 65%
rename from packages/blockly/scripts/gulpfiles/build_tasks.mjs
rename to packages/blockly/scripts/build.mjs
index 5bcaf4b2a0f..434408892d3 100644
--- a/packages/blockly/scripts/gulpfiles/build_tasks.mjs
+++ b/packages/blockly/scripts/build.mjs
@@ -1,24 +1,26 @@
 /**
  * @license
- * Copyright 2018 Google LLC
+ * Copyright 2026 Raspberry Pi Foundation
  * SPDX-License-Identifier: Apache-2.0
  */
 
 /**
- * @fileoverview Gulp script to build Blockly for Node & NPM.
+ * @fileoverview Script to build the blockly package.
  */
 
-import * as gulp from 'gulp';
-import rename from 'gulp-rename';
-import replace from 'gulp-replace';
-import sourcemaps from 'gulp-sourcemaps';
-
-import * as fs from 'fs';
-import * as fsPromises from 'fs/promises';
-import * as path from 'path';
+import {execSync} from 'child_process';
+import {
+  appendFile,
+  mkdir,
+  readFile,
+  rename,
+  rm,
+  unlink,
+  writeFile,
+} from 'node:fs/promises';
 
 import {globSync} from 'glob';
-import {gulp as closureCompiler} from 'google-closure-compiler';
+import * as path from 'path';
 import yargs from 'yargs';
 import {hideBin} from 'yargs/helpers';
 
@@ -26,22 +28,14 @@ import {
   BUILD_DIR,
   RELEASE_DIR,
   TSC_OUTPUT_DIR,
-} from './config.mjs';
-
-import {posixPath, quote} from '../helpers.js';
-import {getPackageJson} from '../lib/package_json.mjs';
+  TSC_OUTPUT_DIR_POSIX,
+} from './build_constants.mjs';
+import {posixPath, quote} from './helpers.js';
+import {compile} from './lib/build_utils.mjs';
+import {getPackageJson} from './lib/package_json.mjs';
 
 const argv = yargs(hideBin(process.argv)).parse();
 
-////////////////////////////////////////////////////////////
-//                        Build                           //
-////////////////////////////////////////////////////////////
-
-/**
- * Posix version of TSC_OUTPUT_DIR
- */
-const TSC_OUTPUT_DIR_POSIX = posixPath(TSC_OUTPUT_DIR);
-
 /**
  * Suffix to add to compiled output files.
  */
@@ -182,9 +176,10 @@ for (let i = 1; i < chunks.length; i++) {
  * with an arbitrary, very short name.
  *
  * Nevertheless, this function can still be used to compute the
- * location of @defined variables, because --define directives are
+ * location of `@define`d variables, because --define directives are
  * processed before the final renaming occurs.
- */ 
+ * @param {{entry: string}} chunk The chunk whose module path to compute.
+ */
 function modulePath(chunk) {
   const entryPath = path.posix.join(TSC_OUTPUT_DIR_POSIX, chunk.entry);
   return 'module$' + entryPath.replace(/\.js$/, '').replaceAll('/', '$');
@@ -199,127 +194,28 @@ const licenseRegex = `\\/\\*\\*
 
 /**
  * Helper method for stripping the Google's and MIT's Apache Licenses.
- */
-function stripApacheLicense() {
-  // Strip out Google's and MIT's Apache licences.
-  // Closure Compiler preserves dozens of Apache licences in the Blockly code.
-  // Remove these if they belong to Google or MIT.
-  // MIT's permission to do this is logged in Blockly issue #2412.
-  return replace(new RegExp(licenseRegex, 'g'), '\n\n\n\n');
-  // Replace with the same number of lines so that source-maps are not affected.
-}
-
-/**
- * Closure Compiler diagnostic groups we want to be treated as errors.
- * These are effected when the --debug or --strict flags are passed.
- * For a full list of Closure Compiler groups, consult the output of
- * google-closure-compiler --help or look in the source  here:
- * https://github.com/google/closure-compiler/blob/master/src/com/google/javascript/jscomp/DiagnosticGroups.java#L117
- *
- * The list in JSCOMP_ERROR contains all the diagnostic groups we know
- * about, but some are commented out if we don't want them, and may
- * appear in JSCOMP_WARNING or JSCOMP_OFF instead.  Items not
- * appearing on any list will default to setting provided by the
- * compiler, which may vary depending on compilation level.
- */
-const JSCOMP_ERROR = [
-  // 'accessControls',  // Deprecated; means same as visibility.
-  // 'checkPrototypalTypes',  // override annotations are stripped by tsc.
-  'checkRegExp',
-  // 'checkTypes',  // Disabled; see note in JSCOMP_OFF.
-  'checkVars',
-  'conformanceViolations',
-  'const',
-  'constantProperty',
-  'duplicateMessage',
-  'es5Strict',
-  'externsValidation',
-  'extraRequire', // Undocumented but valid.
-  'functionParams',
-  // 'globalThis',  // This types are stripped by tsc.
-  'invalidCasts',
-  'misplacedTypeAnnotation',
-  // 'missingOverride',  // There are many of these, which should be fixed.
-  'missingPolyfill',
-  // 'missingProperties',  // Unset static properties are stripped by tsc.
-  'missingProvide',
-  'missingRequire',
-  'missingReturn',
-  // 'missingSourcesWarnings',  // Group of several other options.
-  'moduleLoad',
-  'msgDescriptions',
-  // 'nonStandardJsDocs',  // Disabled; see note in JSCOMP_OFF.
-  // 'partialAlias',  // Don't want this to be an error yet; only warning.
-  // 'polymer',  // Not applicable.
-  // 'reportUnknownTypes',  // VERY verbose.
-  // 'strictCheckTypes',  // Use --strict to enable.
-  // 'strictMissingProperties',  // Part of strictCheckTypes.
-  'strictModuleChecks', // Undocumented but valid.
-  'strictModuleDepCheck',
-  // 'strictPrimitiveOperators',  // Part of strictCheckTypes.
-  'suspiciousCode',
-  'typeInvalidation',
-  'undefinedVars',
-  'underscore',
-  'unknownDefines',
-  // 'unusedLocalVariables',  // Disabled; see note in JSCOMP_OFF.
-  'uselessCode',
-  'untranspilableFeatures',
-  // 'visibility',  // Disabled; see note in JSCOMP_OFF.
-];
-
-/**
- * Closure Compiler diagnostic groups we want to be treated as warnings.
- * These are effected when the --debug or --strict flags are passed.
- *
- * For most (all?) diagnostic groups this is the default level, so
- * it's generally sufficient to remove them from JSCOMP_ERROR.
- */
-const JSCOMP_WARNING = ['deprecated', 'deprecatedAnnotations'];
-
-/**
- * Closure Compiler diagnostic groups we want to be ignored.  These
- * suppressions are always effected by default.
  *
- * Make sure that anything added here is commented out of JSCOMP_ERROR
- * above, as that takes precedence.)
+ * @param {!Array<string>} filePaths Files to rewrite.
  */
-const JSCOMP_OFF = [
-  /* The removal of Closure type system types from our JSDoc
-   * annotations means that the Closure Compiler now generates certain
-   * diagnostics because it no longer has enough information to be
-   * sure that the input code is correct.  The following diagnostic
-   * groups are turned off to suppress such errors.
-   *
-   * When adding additional items to this list it may be helpful to
-   * search the compiler source code
-   * (https://github.com/google/closure-compiler/) for the JSC_*
-   * diagnostic name (omitting the JSC_ prefix) to find the corresponding
-   * DiagnosticGroup.
-   */
-  'checkTypes',
-  'nonStandardJsDocs', // Due to @internal
-  'unusedLocalVariables', // Due to code generated for merged namespaces.
-
-  /* In order to transition to ES modules, modules will need to import
-   * one another by relative paths. This means that the previous
-   * practice of moving all source files into the same directory for
-   * compilation would break imports.
-   *
-   * Not flattening files in this way breaks our usage
-   * of @package however: files were flattened so that all Blockly
-   * source files are in the same directory and can use @package to
-   * mark methods that are only allowed for use by Blockly, while
-   * still allowing access between e.g. core/events/* and
-   * core/utils/*. We were downgrading access control violations
-   * (including @private) to warnings, but this ends up being so
-   * spammy that it makes the compiler output nearly useless.
-   *
-   * Once ES module migration is complete, they will be re-enabled and
-   * an alternative to @package will be established.
-   */
-  'visibility',
-];
+async function stripApacheLicenses(filePaths) {
+  await Promise.all(
+    filePaths.map(async (filePath) => {
+      const source = await readFile(filePath, 'utf8');
+      // Strip out Google's, MIT's, and Raspberry Pi Foundation's Apache
+      // licences. Closure Compiler preserves dozens of Apache licences in the
+      // Blockly code. Remove these if they belong to Google, MIT, or Raspberry
+      // Pi Foundation.
+      // MIT's permission to do this is logged in Blockly issue #2412.
+      const stripped = source.replace(
+        new RegExp(licenseRegex, 'g'),
+        '\n\n\n\n',
+      );
+      // Replace with the same number of lines so that source-maps are
+      // not affected.
+      if (stripped !== source) await writeFile(filePath, stripped);
+    }),
+  );
+}
 
 /**
  * Return the path to the generated chunk exporter for the given
@@ -327,7 +223,7 @@ const JSCOMP_OFF = [
  *
  * See buildChunkExporters for additional information.
  *
- * @param {{name: string}} chunk
+ * @param {{name: string}} chunk The chunk whose exporter path to compute.
  * @return {string}
  */
 function chunkExporterPath(chunk) {
@@ -393,7 +289,7 @@ function chunkExporterPath(chunk) {
  */
 async function buildChunkExporters() {
   const outDir = path.join(TSC_OUTPUT_DIR, CHUNK_EXPORTERS_DIR);
-  await fsPromises.mkdir(outDir, {recursive: true});
+  await mkdir(outDir, {recursive: true});
 
   await Promise.all(
     chunks.map(async (chunk) => {
@@ -401,7 +297,7 @@ async function buildChunkExporters() {
       const importPath = posixPath(
         path.posix.relative(path.posix.dirname(filename), chunk.entry),
       );
-      await fsPromises.writeFile(
+      await writeFile(
         path.join(TSC_OUTPUT_DIR, filename),
         // Suppress undefined-variable diagnostics, since Closure
         // Compiler can't see the declaration of NAMESPACE_VARIABLE
@@ -420,6 +316,9 @@ ${NAMESPACE_VARIABLE}['${CHUNK_EXPORTS_PREFIX}${chunk.name}'] = exports;
  * A helper method to return an Closure Compiler chunk wrapper that
  * wraps the compiler output for the given chunk in a Universal Module
  * Definition.
+ * @param {{name: string, parent: ?object, scriptExport: string,
+ *     scriptNamedExports: ({[key: string]: string}|undefined)}} chunk
+ *     The chunk to generate a UMD wrapper for.
  */
 function chunkWrapper(chunk) {
   // Each chunk can have only a single dependency, which is its parent
@@ -453,7 +352,7 @@ function chunkWrapper(chunk) {
   const scriptExportStatements = [
     `root.${chunk.scriptExport} = factory(${scriptDepsExpr});`,
   ];
-  for (var location in chunk.scriptNamedExports) {
+  for (let location in chunk.scriptNamedExports) {
     const namedExport = chunk.scriptNamedExports[location];
     scriptExportStatements.push(
       `root.${location} = root.${chunk.scriptExport}.${namedExport};`,
@@ -550,41 +449,16 @@ function getChunkOptions() {
   return {chunk: chunkOptions, js: allFiles, chunk_wrapper: chunkWrappers};
 }
 
-/**
- * Helper method for calling the Closure Compiler, establishing
- * default options (that can be overridden by the caller).
- * @param {*} options Caller-supplied options that will override the
- *     defaultOptions.
- */
-function compile(options) {
-  const defaultOptions = {
-    compilation_level: 'SIMPLE_OPTIMIZATIONS',
-    warning_level: argv.verbose ? 'VERBOSE' : 'DEFAULT',
-    language_in: 'ECMASCRIPT_2020',
-    language_out: 'ECMASCRIPT_2015',
-    jscomp_off: [...JSCOMP_OFF],
-    rewrite_polyfills: true,
-    hide_warnings_for: ['node_modules'],
-    define: ['COMPILED=true'],
-  };
-  if (argv.debug || argv.strict) {
-    defaultOptions.jscomp_error = [...JSCOMP_ERROR];
-    defaultOptions.jscomp_warning = [...JSCOMP_WARNING];
-    if (argv.strict) {
-      defaultOptions.jscomp_error.push('strictCheckTypes');
-    }
-  }
-  // Extra options for Closure Compiler gulp plugin.
-  const platform = ['native'];
-
-  return closureCompiler({...defaultOptions, ...options}, {platform});
-}
-
 /**
  * This task compiles the core library, blocks and generators, creating
  * blockly_compressed.js, blocks_compressed.js, etc.
  */
-function buildCompiled() {
+async function buildCompiled() {
+  // Closure writes each chunk's bare output here rather than straight into
+  // RELEASE_DIR, so it can't overwrite files already in dist/ (package.mjs
+  // writes legacy shims named blocks.js, dart.js, etc., which collide with
+  // Closure's bare chunk output).
+  const compiledDir = path.join(BUILD_DIR, 'compiled');
   // Get chunking.
   const chunkOptions = getChunkOptions();
   // Closure Compiler options.
@@ -600,23 +474,58 @@ function buildCompiled() {
     // by the time --define is processed.)  See
     // https://github.com/google/closure-compiler/issues/1601#issuecomment-483452226
     define: `VERSION$$${modulePath(chunks[0])}='${packageJson.version}'`,
+    js: chunkOptions.js,
     chunk: chunkOptions.chunk,
     chunk_wrapper: chunkOptions.chunk_wrapper,
-    // Don't supply the list of source files in chunkOptions.js as an
-    // option to Closure Compiler; instead feed them as input via gulp.src.
+    // Closure writes one file per chunk, named after the chunk, so
+    // this produces e.g. build/compiled/blockly.js; the file is then
+    // renamed with COMPILED_SUFFIX and moved into RELEASE_DIR below.
+    chunk_output_path_prefix: `${compiledDir}/`,
+    create_source_map: '%outname%.map',
     rename_prefix_namespace: NAMESPACE_VARIABLE,
     assume_function_wrapper: true,
   };
 
-  // Fire up compilation pipline.
-  return gulp
-    .src(chunkOptions.js, {base: './'})
-    .pipe(stripApacheLicense())
-    .pipe(sourcemaps.init())
-    .pipe(compile(options))
-    .pipe(rename({suffix: COMPILED_SUFFIX}))
-    .pipe(sourcemaps.write('.'))
-    .pipe(gulp.dest(RELEASE_DIR));
+  await stripApacheLicenses(chunkOptions.js);
+  // Start from an empty scratch directory and ensure the destination exists.
+  await rm(compiledDir, {recursive: true, force: true});
+  await mkdir(compiledDir, {recursive: true});
+  await mkdir(RELEASE_DIR, {recursive: true});
+  await compile(options, argv);
+  for (const chunk of chunks) {
+    const compiledPath = path.join(compiledDir, `${chunk.name}.js`);
+    const outputName = `${chunk.name}${COMPILED_SUFFIX}.js`;
+    const outputPath = path.join(RELEASE_DIR, outputName);
+
+    // Closure's --chunk_output_path_prefix write path appends one extra
+    // trailing blank line beyond what's in chunk_wrapper. Trim it here so the
+    // .js and its .map stay consistent with each other.
+    let code = await readFile(compiledPath, 'utf8');
+    if (code.endsWith('\n\n')) {
+      code = code.slice(0, -1);
+      await writeFile(compiledPath, code);
+    }
+
+    const sourceMap = JSON.parse(await readFile(`${compiledPath}.map`, 'utf8'));
+    sourceMap.file = outputName;
+    if (sourceMap.mappings.endsWith(';')) {
+      sourceMap.mappings = sourceMap.mappings.slice(0, -1);
+    }
+    sourceMap.sourcesContent = await Promise.all(
+      sourceMap.sources.map((source) =>
+        readFile(source, 'utf8').catch(() => null),
+      ),
+    );
+
+    await writeFile(`${outputPath}.map`, JSON.stringify(sourceMap));
+    await unlink(`${compiledPath}.map`);
+
+    await rename(compiledPath, outputPath);
+    await appendFile(
+      outputPath,
+      `\n\n//# sourceMappingURL=${outputName}.map\n`,
+    );
+  }
 }
 
 /**
@@ -635,13 +544,13 @@ async function buildShims() {
   // .js files therein are ESM not CJS, so we can import the
   // entrypoints to enumerate their exported names.
   const TMP_PACKAGE_JSON = path.join(BUILD_DIR, 'package.json');
-  await fsPromises.writeFile(TMP_PACKAGE_JSON, '{"type": "module"}');
+  await writeFile(TMP_PACKAGE_JSON, '{"type": "module"}');
 
   await Promise.all(
     chunks.map(async (chunk) => {
       // Import chunk entrypoint to get names of exports for chunk.
       const entryPath = path.posix.join(TSC_OUTPUT_DIR_POSIX, chunk.entry);
-      const exportedNames = Object.keys(await import(`../../${entryPath}`));
+      const exportedNames = Object.keys(await import(`../${entryPath}`));
 
       // Write an ESM wrapper that imports the CJS module and re-exports
       // its named exports.
@@ -649,7 +558,7 @@ async function buildShims() {
       const wrapperPath = path.join(RELEASE_DIR, `${chunk.name}.mjs`);
       const importName = chunk.scriptExport.replace(/.*\./, '');
 
-      await fsPromises.writeFile(
+      await writeFile(
         wrapperPath,
         `import ${importName} from '${cjsPath}';
 export const {
@@ -661,7 +570,7 @@ ${exportedNames.map((name) => `  ${name},`).join('\n')}
       // For first chunk, write an additional ESM wrapper for 'blockly'
       // entrypoint since it has the same exports as 'blockly/core'.
       if (chunk.name === 'blockly') {
-        await fsPromises.writeFile(
+        await writeFile(
           path.join(RELEASE_DIR, `index.mjs`),
           `import Blockly from './index.js';
 export const {
@@ -683,7 +592,7 @@ ${exportedNames.map((name) => `  ${name},`).join('\n')}
         ? `import ${quote(`./${chunk.parent.name}.loader.mjs`)};`
         : '';
 
-      await fsPromises.writeFile(
+      await writeFile(
         shimPath,
         `import {loadChunk} from '../tests/scripts/load.mjs';
 ${parentImport}
@@ -700,58 +609,26 @@ ${exportedNames.map((name) => `  ${name},`).join('\n')}
     }),
   );
 
-  await fsPromises.rm(TMP_PACKAGE_JSON);
+  await rm(TMP_PACKAGE_JSON);
 }
 
 /**
- * This task uses Closure Compiler's ADVANCED_OPTIMIZATIONS mode to
- * compile together Blockly core, blocks and generators with a simple
- * test app; the purpose is to verify that Blockly is compatible with
- * the ADVANCED_OPTIMIZATIONS mode.
+ * Executes the langfiles command.
+ */
+function execLangFiles() {
+  execSync('npm run langfiles', {stdio: 'inherit'});
+}
+
+/**
+ * Build all chunks, compressed files, sourcemaps, shims, and langfiles.
  *
  * Prerequisite: tsc.
  */
-function compileAdvancedCompilationTest() {
-  // If main_compressed.js exists (from a previous run) delete it so that
-  // a later browser-based test won't check it should the compile fail.
-  try {
-    fs.unlinkSync('./tests/compile/main_compressed.js');
-  } catch {
-    // Probably it didn't exist.
-  }
-
-  const srcs = [
-    TSC_OUTPUT_DIR + '/**/*.js',
-    'tests/compile/main.js',
-    'tests/compile/test_blocks.js',
-  ];
-
-  // Closure Compiler options.
-  const options = {
-    dependency_mode: 'PRUNE',
-    compilation_level: 'ADVANCED_OPTIMIZATIONS',
-    entry_point: './tests/compile/main.js',
-    js_output_file: 'main_compressed.js',
-  };
-  return gulp
-    .src(srcs, {base: './'})
-    .pipe(stripApacheLicense())
-    .pipe(sourcemaps.init())
-    .pipe(compile(options))
-    .pipe(sourcemaps.write('.', {includeContent: false, sourceRoot: '../../'}))
-    .pipe(gulp.dest('./tests/compile/'));
+async function build() {
+  await buildChunkExporters();
+  await buildCompiled();
+  await buildShims();
+  execLangFiles();
 }
 
-// function tsc, above
-export const minify = gulp.series(
-  buildChunkExporters,
-  buildCompiled,
-  buildShims,
-);
-export const build = minify;
-
-// Manually-invokable targets, with prerequisites where required.
-// function messages, above
-export const buildAdvancedCompilationTest = gulp.series(
-  compileAdvancedCompilationTest,
-);
+await build();
diff --git a/packages/blockly/scripts/build_constants.mjs b/packages/blockly/scripts/build_constants.mjs
index b07c593fec1..f0bc4ca2da2 100644
--- a/packages/blockly/scripts/build_constants.mjs
+++ b/packages/blockly/scripts/build_constants.mjs
@@ -1,5 +1,7 @@
 import * as path from 'path';
 
+import {posixPath} from './helpers.js';
+
 // Paths are all relative to the repository root.  Do not include
 // trailing slash.
 
@@ -19,6 +21,11 @@ export const TSC_OUTPUT_DIR = path.join(BUILD_DIR, 'src');
 // Directory for files generated by compiling test code.
 export const TEST_TSC_OUTPUT_DIR = path.join(BUILD_DIR, 'tests');
 
+/**
+ * Posix version of TSC_OUTPUT_DIR
+ */
+export const TSC_OUTPUT_DIR_POSIX = posixPath(TSC_OUTPUT_DIR);
+
 // Directory in which to assemble (and from which to publish) the
 // blockly npm package.
 export const RELEASE_DIR = 'dist';
diff --git a/packages/blockly/scripts/gulpfiles/appengine_tasks.mjs b/packages/blockly/scripts/gulpfiles/appengine_tasks.mjs
index ff207bc7910..6223e095ad7 100644
--- a/packages/blockly/scripts/gulpfiles/appengine_tasks.mjs
+++ b/packages/blockly/scripts/gulpfiles/appengine_tasks.mjs
@@ -12,13 +12,13 @@ import * as gulp from 'gulp';
 
 import * as fs from 'fs';
 import {execSync} from 'child_process';
-import * as buildTasks from './build_tasks.mjs';
 import {getPackageJson} from '../lib/package_json.mjs';
 import {cleanBuildDir, cleanReleaseDir} from '../lib/fs_utils.mjs';
 import {rimraf} from 'rimraf';
 
-const demoTmpDir = '../_deploy';
-const demoStaticTmpDir = '../_deploy/static';
+const demoTmpDir = '_deploy';
+const demoStaticTmpDir = '_deploy/static';
+const demoStaticBlocklyDir = '_deploy/static/packages/blockly';
 
 /**
  * Cleans and creates the tmp directory used for deploying.
@@ -50,8 +50,8 @@ function copyStaticSrc(done) {
  * Prerequisite: clean, build.
  */
 function copyBuilt(done) {
-  return gulp.src(['build/msg/*', 'dist/*_compressed.js*', 'build/*.loader.mjs'], {base: '.'})
-      .pipe(gulp.dest(demoStaticTmpDir));
+  return gulp.src(['build/src/**/*', 'build/msg/*', 'dist/*_compressed.js*', 'build/*.loader.mjs'], {base: '.'})
+      .pipe(gulp.dest(demoStaticBlocklyDir));
 }
 
 /**
@@ -75,7 +75,7 @@ function copyCompressedToOldLocation(done) {
  */
 function copyMessagesToOldLocation(done) {
   return gulp.src(['build/msg/*'])
-      .pipe(gulp.dest(demoStaticTmpDir + '/msg/js'));
+      .pipe(gulp.dest(`${demoStaticTmpDir}/msg/js`));
 }
 
 /**
@@ -83,8 +83,8 @@ function copyMessagesToOldLocation(done) {
  */
 function copyAppengineSrc() {
   const appengineSrc = [
-      `${demoStaticTmpDir}/appengine/**/*`,
-      `${demoStaticTmpDir}/appengine/.gcloudignore`,
+      `${demoStaticBlocklyDir}/appengine/**/*`,
+      `${demoStaticBlocklyDir}/appengine/.gcloudignore`,
   ];
   return gulp.src(appengineSrc).pipe(gulp.dest(demoTmpDir));
 }
@@ -94,12 +94,11 @@ function copyAppengineSrc() {
  */
 function copyPlaygroundDeps() {
   const playgroundDeps = [
-      './node_modules/@blockly/dev-tools/dist/index.js',
-      './node_modules/@blockly/theme-modern/dist/index.js',
-      './node_modules/@blockly/block-test/dist/index.js',
-      './node_modules/@blockly/keyboard-navigation/dist/index.js',
+      '../../node_modules/@blockly/dev-tools/dist/index.js',
+      '../../node_modules/@blockly/theme-modern/dist/index.js',
+      '../../node_modules/@blockly/block-test/dist/index.js',
   ];
-  return gulp.src(playgroundDeps, {base: '.'}).pipe(gulp.dest(demoStaticTmpDir));
+  return gulp.src(playgroundDeps, {base: '../..'}).pipe(gulp.dest(demoStaticBlocklyDir));
 }
 
 /**
@@ -157,6 +156,14 @@ function deployBetaAndClean(done) {
   done();
 }
 
+/**
+ * Executes the build command.
+ */
+function execBuild(done) {
+  execSync('npm run build', {stdio: 'inherit'});
+  done()
+}
+
 /**
  * Prepares demos.
  *
@@ -171,7 +178,7 @@ export const prepareDemos = gulp.series(
         gulp.series(
             gulp.parallel(cleanBuildDir,
                           cleanReleaseDir),
-            buildTasks.build,
+            execBuild,
             gulp.parallel(copyBuilt,
                           copyCompressedToOldLocation,
                           copyMessagesToOldLocation)),
diff --git a/packages/blockly/scripts/lib/build_utils.mjs b/packages/blockly/scripts/lib/build_utils.mjs
new file mode 100644
index 00000000000..db7830082b7
--- /dev/null
+++ b/packages/blockly/scripts/lib/build_utils.mjs
@@ -0,0 +1,199 @@
+/**
+ * @license
+ * Copyright 2026 Raspberry Pi Foundation
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @fileoverview Helpers for building/compiling using Googles Closure Compiler.
+ */
+
+import {compiler as ClosureCompiler} from 'google-closure-compiler';
+import {getNativeImagePath} from 'google-closure-compiler/lib/utils.js';
+
+/**
+ * Closure Compiler diagnostic groups we want to be treated as errors.
+ * These are effected when the --debug or --strict flags are passed.
+ * For a full list of Closure Compiler groups, consult the output of
+ * google-closure-compiler --help or look in the source  here:
+ * https://github.com/google/closure-compiler/blob/master/src/com/google/javascript/jscomp/DiagnosticGroups.java#L117
+ *
+ * The list in JSCOMP_ERROR contains all the diagnostic groups we know
+ * about, but some are commented out if we don't want them, and may
+ * appear in JSCOMP_WARNING or JSCOMP_OFF instead.  Items not
+ * appearing on any list will default to setting provided by the
+ * compiler, which may vary depending on compilation level.
+ */
+const JSCOMP_ERROR = [
+  // 'accessControls',  // Deprecated; means same as visibility.
+  // 'checkPrototypalTypes',  // override annotations are stripped by tsc.
+  'checkRegExp',
+  // 'checkTypes',  // Disabled; see note in JSCOMP_OFF.
+  'checkVars',
+  'conformanceViolations',
+  'const',
+  'constantProperty',
+  'duplicateMessage',
+  'es5Strict',
+  'externsValidation',
+  'extraRequire', // Undocumented but valid.
+  'functionParams',
+  // 'globalThis',  // This types are stripped by tsc.
+  'invalidCasts',
+  'misplacedTypeAnnotation',
+  // 'missingOverride',  // There are many of these, which should be fixed.
+  'missingPolyfill',
+  // 'missingProperties',  // Unset static properties are stripped by tsc.
+  'missingProvide',
+  'missingRequire',
+  'missingReturn',
+  // 'missingSourcesWarnings',  // Group of several other options.
+  'moduleLoad',
+  'msgDescriptions',
+  // 'nonStandardJsDocs',  // Disabled; see note in JSCOMP_OFF.
+  // 'partialAlias',  // Don't want this to be an error yet; only warning.
+  // 'polymer',  // Not applicable.
+  // 'reportUnknownTypes',  // VERY verbose.
+  // 'strictCheckTypes',  // Use --strict to enable.
+  // 'strictMissingProperties',  // Part of strictCheckTypes.
+  'strictModuleChecks', // Undocumented but valid.
+  'strictModuleDepCheck',
+  // 'strictPrimitiveOperators',  // Part of strictCheckTypes.
+  'suspiciousCode',
+  'typeInvalidation',
+  'undefinedVars',
+  'underscore',
+  'unknownDefines',
+  // 'unusedLocalVariables',  // Disabled; see note in JSCOMP_OFF.
+  'uselessCode',
+  'untranspilableFeatures',
+  // 'visibility',  // Disabled; see note in JSCOMP_OFF.
+];
+
+/**
+ * Closure Compiler diagnostic groups we want to be treated as warnings.
+ * These are effected when the --debug or --strict flags are passed.
+ *
+ * For most (all?) diagnostic groups this is the default level, so
+ * it's generally sufficient to remove them from JSCOMP_ERROR.
+ */
+const JSCOMP_WARNING = ['deprecated', 'deprecatedAnnotations'];
+
+/**
+ * Closure Compiler diagnostic groups we want to be ignored.  These
+ * suppressions are always effected by default.
+ *
+ * Make sure that anything added here is commented out of JSCOMP_ERROR
+ * above, as that takes precedence.)
+ */
+const JSCOMP_OFF = [
+  /* The removal of Closure type system types from our JSDoc
+   * annotations means that the Closure Compiler now generates certain
+   * diagnostics because it no longer has enough information to be
+   * sure that the input code is correct.  The following diagnostic
+   * groups are turned off to suppress such errors.
+   *
+   * When adding additional items to this list it may be helpful to
+   * search the compiler source code
+   * (https://github.com/google/closure-compiler/) for the JSC_*
+   * diagnostic name (omitting the JSC_ prefix) to find the corresponding
+   * DiagnosticGroup.
+   */
+  'checkTypes',
+  'nonStandardJsDocs', // Due to @internal
+  'unusedLocalVariables', // Due to code generated for merged namespaces.
+
+  /* In order to transition to ES modules, modules will need to import
+   * one another by relative paths. This means that the previous
+   * practice of moving all source files into the same directory for
+   * compilation would break imports.
+   *
+   * Not flattening files in this way breaks our usage
+   * of @package however: files were flattened so that all Blockly
+   * source files are in the same directory and can use @package to
+   * mark methods that are only allowed for use by Blockly, while
+   * still allowing access between e.g. core/events/* and
+   * core/utils/*. We were downgrading access control violations
+   * (including @private) to warnings, but this ends up being so
+   * spammy that it makes the compiler output nearly useless.
+   *
+   * Once ES module migration is complete, they will be re-enabled and
+   * an alternative to @package will be established.
+   */
+  'visibility',
+];
+
+/**
+ * Helper method for fetching the default closure compiler options.
+ *
+ * @param {string[]} argv The arguments passed in from the command line.
+ */
+function getDefaultCompileOptions(argv) {
+  const defaultOptions = {
+    compilation_level: 'SIMPLE_OPTIMIZATIONS',
+    warning_level: argv?.verbose ? 'VERBOSE' : 'DEFAULT',
+    language_in: 'ECMASCRIPT_2020',
+    language_out: 'ECMASCRIPT_2015',
+    jscomp_off: [...JSCOMP_OFF],
+    rewrite_polyfills: true,
+    hide_warnings_for: ['node_modules'],
+    define: ['COMPILED=true'],
+  };
+  if (argv?.debug || argv?.strict) {
+    defaultOptions.jscomp_error = [...JSCOMP_ERROR];
+    defaultOptions.jscomp_warning = [...JSCOMP_WARNING];
+    if (argv?.strict) {
+      defaultOptions.jscomp_error.push('strictCheckTypes');
+    }
+  }
+  return defaultOptions;
+}
+
+/**
+ * Helper method for calling the Closure Compiler, establishing
+ * default options (that can be overridden by the caller).
+ *
+ * The compiler reads its inputs from and writes its outputs to disk,
+ * so the caller is expected to supply --js and either --js_output_file
+ * or --chunk_output_path_prefix.
+ *
+ * @param {{[flag: string]: string|boolean|!Array<string>}} options
+ *     Caller-supplied options that will override the defaultOptions.
+ * @param {string[]} argv The arguments passed in from the command line.
+ * @return {!Promise<string>} Resolves with the compiler's stdout once
+ *     it exits successfully; rejects if it exits non-zero.
+ */
+export function compile(options, argv) {
+  const compilerInstance = new ClosureCompiler({
+    ...getDefaultCompileOptions(argv),
+    ...options,
+  });
+
+  // google-closure-compiler's node API always shells out to `java`
+  // unless JAR_PATH is cleared; only its gulp and grunt plugins know
+  // about the platform-native binaries.  Do what those plugins do, so
+  // that a JRE isn't needed on platforms we ship a binary for.  See
+  // getFirstSupportedPlatform() in google-closure-compiler/lib/utils.js.
+  const nativeImagePath = getNativeImagePath();
+  if (nativeImagePath) {
+    compilerInstance.JAR_PATH = null;
+    compilerInstance.javaPath = nativeImagePath;
+  } else if (!process.env.JAVA_HOME) {
+    throw new Error(
+      'No native Closure Compiler binary for this platform and no JRE ' +
+        'found; set JAVA_HOME or install google-closure-compiler-<platform>.',
+    );
+  }
+
+  return new Promise((resolve, reject) => {
+    compilerInstance.run((exitCode, stdout, stderr) => {
+      // Diagnostics go to stderr even when compilation succeeds.
+      if (stderr) process.stderr.write(stderr);
+      if (exitCode === 0) {
+        resolve(stdout);
+      } else {
+        reject(new Error(`Closure Compiler exited with code ${exitCode}.`));
+      }
+    });
+  });
+}
diff --git a/packages/blockly/tests/compile/test_compile_advanced.mjs b/packages/blockly/tests/compile/test_compile_advanced.mjs
new file mode 100644
index 00000000000..36e145bcf41
--- /dev/null
+++ b/packages/blockly/tests/compile/test_compile_advanced.mjs
@@ -0,0 +1,87 @@
+/**
+ * @license
+ * Copyright 2026 Raspberry Pi Foundation
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @fileoverview Test compile for closure compiler's advanced optimizations.
+ */
+
+import {
+  appendFile,
+  readFile,
+  unlink,
+  writeFile,
+} from 'node:fs/promises';
+
+import {globSync} from 'glob';
+import * as path from 'path';
+import yargs from 'yargs';
+import {hideBin} from 'yargs/helpers';
+
+import {posixPath} from '../../scripts/helpers.js';
+import {compile} from '../../scripts/lib/build_utils.mjs';
+import {TSC_OUTPUT_DIR_POSIX} from '../../scripts/build_constants.mjs';
+
+const argv = yargs(hideBin(process.argv)).parse();
+
+/**
+ * Resolve glob patterns to file paths using globSync
+ */
+function globToArray(patterns) {
+  return globSync(patterns, {absolute: true})
+    .map((file) => posixPath(path.relative(process.cwd(), file)))
+    .sort();
+}
+/**
+ * This task uses Closure Compiler's ADVANCED_OPTIMIZATIONS mode to
+ * compile together Blockly core, blocks and generators with a simple
+ * test app; the purpose is to verify that Blockly is compatible with
+ * the ADVANCED_OPTIMIZATIONS mode.
+ *
+ * Prerequisite: tsc.
+ */
+async function compileAdvancedCompilationTest() {
+  const outputPath = path.join('tests', 'compile', 'main_compressed.js');
+  const mapPath = `${outputPath}.map`;
+
+  // If main_compressed.js exists (from a previous run) delete it so that
+  // a later browser-based test won't check it should the compile fail.
+  try {
+    await unlink(outputPath);
+  } catch {
+    // Probably it didn't exist.
+  }
+
+  const mainPath = 'tests/compile/main.js';
+  const srcs = [
+    ...(globToArray(TSC_OUTPUT_DIR_POSIX + '/**/*.js')),
+    mainPath,
+    'tests/compile/test_blocks.js',
+  ];
+
+  const options = {
+    js: srcs,
+    dependency_mode: 'PRUNE',
+    compilation_level: 'ADVANCED_OPTIMIZATIONS',
+    entry_point: './' + mainPath,
+    js_output_file: outputPath,
+    create_source_map: mapPath,
+  };
+
+  await compile(options, argv);
+
+  const sourceMap = JSON.parse(await readFile(mapPath, 'utf8'));
+  sourceMap.file = path.basename(outputPath);
+  sourceMap.sourceRoot = '../../'; 
+  delete sourceMap.sourcesContent;
+
+  await writeFile(mapPath, JSON.stringify(sourceMap));
+  await appendFile(
+    outputPath,
+    `\n//# sourceMappingURL=${path.basename(mapPath)}\n`,
+  );
+}
+
+await compileAdvancedCompilationTest();