feat(core): add package exports map for ESM subpath resolution

BREAKING.md

@@ -15,6 +15,7 @@ This is a comprehensive list of the breaking changes introduced in the major ver
 ## Version 9.x
 
 - [Browser and Platform Support](#version-9x-browser-platform-support)
+- [Package Exports](#version-9x-package-exports)
 - [Components](#version-9x-components)
   - [Legacy Picker](#version-9x-legacy-picker)
   - [Router Outlet](#version-9x-router-outlet)
@@ -32,6 +33,23 @@ This section details the desktop browser, JavaScript framework, and mobile platf
 | --------- | --------------------- |
 | React     | 18+                   |
 
+<h2 id="version-9x-package-exports">Package Exports</h2>
+
+`@ionic/core`'s `package.json` now declares an `exports` field. Subpaths like `@ionic/core/components` and `@ionic/core/loader` previously failed under Node ESM (Angular 21's default Vitest builder, raw Node, etc.) with `ERR_UNSUPPORTED_DIR_IMPORT`, because the strict ESM resolver doesn't read the nested `package.json` files this package relied on. The new `exports` map declares the documented subpaths explicitly.
+
+`exports` is an allowlist. Apps using Node ESM, webpack 5, or TypeScript `moduleResolution: "bundler"`/`"node16"`/`"nodenext"` that import from undocumented internal paths need to switch to one of the supported subpaths:
+
+| Subpath                            | Use                                                   |
+| ---------------------------------- | ----------------------------------------------------- |
+| `@ionic/core`                      | Root entry, controllers, animation builders           |
+| `@ionic/core/components`           | Custom-element constructors and shared utilities      |
+| `@ionic/core/components/ion-*.js`  | Single-component custom-element constructor           |
+| `@ionic/core/loader`               | `defineCustomElements` lazy loader                    |
+| `@ionic/core/hydrate`              | SSR hydration entry                                   |
+| `@ionic/core/css/*.css`            | Global stylesheets and palettes                       |
+
+Apps on `moduleResolution: "node"` (classic) and webpack 4 keep resolving through the legacy fields and are unaffected.
+
 <h2 id="version-9x-components">Components</h2>
 
 <h4 id="version-9x-legacy-picker">Legacy Picker</h4>

core/package.json

@@ -26,6 +26,38 @@
   "collection:main": "dist/collection/index.js",
   "collection": "dist/collection/collection-manifest.json",
   "types": "dist/types/interface.d.ts",
+  "exports": {
+    ".": {
+      "types": "./dist/types/interface.d.ts",
+      "import": "./dist/index.js",
+      "require": "./dist/index.cjs.js",
+      "default": "./dist/index.js"
+    },
+    "./components": {
+      "types": "./components/custom-elements.d.ts",
+      "import": "./components/index.js",
+      "default": "./components/index.js"
+    },
+    "./components/*": "./components/*",
+    "./loader": {
+      "types": "./loader/index.d.ts",
+      "import": "./loader/index.js",
+      "require": "./loader/index.cjs.js",
+      "default": "./loader/index.js"
+    },
+    "./loader/*": "./loader/*",
+    "./hydrate": {
+      "types": "./hydrate/index.d.ts",
+      "import": "./hydrate/index.mjs",
+      "require": "./hydrate/index.js",
+      "default": "./hydrate/index.js"
+    },
+    "./hydrate/*": "./hydrate/*",
+    "./css/*.css": "./css/*.css",
+    "./css/*": "./css/*",
+    "./dist/*": "./dist/*",
+    "./package.json": "./package.json"
+  },
   "files": [
     "components/",
     "css/",