feat(nextjs): export Mosaic UserButton from an experimental subpath

Adds `@clerk/nextjs/experimental/mosaic` (via `@clerk/react` and `@clerk/ui`)
so the Mosaic UserButton can mount directly in a host app's tree, plus the
matching `experimental/mosaic/styles.css`.

The `@clerk/ui` mosaic entry is now a client boundary in whole (the bundle
collapses the per-file directives) and is guarded against Emotion creeping
back in, which meant replacing the UserButton trigger skeleton with StyleX.

Author: alexcarpenter

.changeset/mosaic-experimental-export.md

@@ -0,0 +1,21 @@
+---
+'@clerk/nextjs': minor
+'@clerk/react': minor
+'@clerk/ui': minor
+---
+
+Add an experimental subpath for Mosaic components that mount directly in your app's tree rather than being rendered by clerk-js. `UserButton` is the first one. It reads Clerk through hooks, so a `ClerkProvider` above it is all it needs:
+
+```tsx
+import { UserButton } from '@clerk/nextjs/experimental/mosaic';
+```
+
+Pair it with the stylesheet, which carries the design tokens and every component rule:
+
+```css
+@import '@clerk/nextjs/experimental/mosaic/styles.css' layer(clerk);
+```
+
+The surface and the components behind it will change without a major version while they are experimental.
+
+In `@clerk/ui`, the Mosaic stylesheet moves from `@clerk/ui/styles.css` to `@clerk/ui/experimental/mosaic/styles.css` to sit alongside the components it styles. Update the import if you were using it.

.claude/skills/mosaic/references/stylex.md

@@ -621,8 +621,8 @@ export interface PopoverPopupProps extends MosaicComponentProps<'div'> { … }
 
 - **Published** (`build:mosaic` → `@stylexjs/rollup-plugin`): compiles the
   `styles/index.ts` barrel into `dist-mosaic/styles.css`, exported as
-  `@clerk/ui/styles.css`. Consumers choose the cascade layer at import:
-  `@import '@clerk/ui/styles.css' layer(components)`.
+  `@clerk/ui/experimental/mosaic/styles.css`. Consumers choose the cascade layer at import:
+  `@import '@clerk/ui/experimental/mosaic/styles.css' layer(components)`.
 - **Swingset** (source-consumed): `@stylexjs/unplugin/webpack` in `next.config`
   transforms StyleX **JS only** (calls → static atoms; SWC/Emotion untouched);
   `@stylexjs/postcss-plugin` extracts the **CSS** by replacing `@stylex;` in

packages/nextjs/package.json

@@ -55,6 +55,12 @@
       "import": "./dist/esm/experimental.js",
       "require": "./dist/cjs/experimental.js"
     },
+    "./experimental/mosaic": {
+      "types": "./dist/types/experimental/mosaic.d.ts",
+      "import": "./dist/esm/experimental/mosaic.js",
+      "require": "./dist/cjs/experimental/mosaic.js"
+    },
+    "./experimental/mosaic/styles.css": "./dist/experimental/mosaic/styles.css",
     "./legacy": {
       "types": "./dist/types/legacy.d.ts",
       "import": "./dist/esm/legacy.js",
@@ -70,15 +76,15 @@
     "webhooks"
   ],
   "scripts": {
-    "build": "pnpm clean && tsup",
+    "build": "pnpm clean && tsup && node ../../scripts/copy-mosaic-styles.mjs dist/experimental/mosaic/styles.css",
     "build:declarations": "tsc -p tsconfig.declarations.json",
     "clean": "rimraf ./dist",
     "dev": "tsup --watch",
     "dev:pub": "pnpm dev -- --env.publish",
     "format": "node ../../scripts/format-package.mjs",
     "format:check": "node ../../scripts/format-package.mjs --check",
     "lint": "eslint src",
-    "lint:attw": "attw --pack . --profile node16 --ignore-rules unexpected-module-syntax",
+    "lint:attw": "attw --pack . --exclude-entrypoints experimental/mosaic/styles.css --profile node16 --ignore-rules unexpected-module-syntax",
     "lint:publint": "publint",
     "test": "vitest run",
     "test:watch": "vitest watch"
@@ -91,6 +97,7 @@
     "tslib": "catalog:repo"
   },
   "devDependencies": {
+    "@clerk/ui": "workspace:*",
     "crypto-es": "^2.1.0",
     "next": "15.5.19"
   },

packages/nextjs/src/experimental/mosaic.ts

@@ -0,0 +1,16 @@
+'use client';
+
+/**
+ * Mosaic components mounted directly in the host app's tree, rather than through clerk-js. They
+ * read Clerk via hooks, so a `ClerkProvider` above them is all they need.
+ *
+ * Pair with the stylesheet, which carries the design tokens and every component rule:
+ *
+ * ```css
+ * @import '@clerk/nextjs/experimental/mosaic/styles.css' layer(clerk);
+ * ```
+ *
+ * @experimental The surface and the components behind it are subject to change.
+ */
+export { UserButton } from '@clerk/react/experimental/mosaic';
+export type { UserButtonProps } from '@clerk/react/experimental/mosaic';

packages/react/package.json

@@ -63,6 +63,17 @@
         "default": "./dist/experimental.cjs"
       }
     },
+    "./experimental/mosaic": {
+      "import": {
+        "types": "./dist/experimental/mosaic.d.mts",
+        "default": "./dist/experimental/mosaic.mjs"
+      },
+      "require": {
+        "types": "./dist/experimental/mosaic.d.cts",
+        "default": "./dist/experimental/mosaic.cjs"
+      }
+    },
+    "./experimental/mosaic/styles.css": "./dist/experimental/mosaic/styles.css",
     "./legacy": {
       "import": {
         "types": "./dist/legacy.d.mts",
@@ -88,25 +99,25 @@
     "dist"
   ],
   "scripts": {
-    "build": "tsdown",
+    "build": "tsdown && node ../../scripts/copy-mosaic-styles.mjs dist/experimental/mosaic/styles.css",
     "clean": "rimraf ./dist",
     "dev": "tsdown --watch",
     "dev:pub": "pnpm dev --env.publish",
     "format": "node ../../scripts/format-package.mjs",
     "format:check": "node ../../scripts/format-package.mjs --check",
     "lint": "eslint src",
-    "lint:attw": "attw --pack . --profile node16",
+    "lint:attw": "attw --pack . --exclude-entrypoints experimental/mosaic/styles.css --profile node16",
     "lint:publint": "publint",
     "test": "vitest run",
     "test:watch": "vitest watch"
   },
   "dependencies": {
     "@clerk/shared": "workspace:^",
+    "@clerk/ui": "workspace:^",
     "tslib": "catalog:repo"
   },
   "devDependencies": {
     "@clerk/localizations": "workspace:*",
-    "@clerk/ui": "workspace:*",
     "@types/semver": "^7.7.1",
     "semver": "^7.8.5",
     "yaml": "^2.9.0"

packages/react/src/experimental/mosaic.ts

@@ -0,0 +1,14 @@
+/**
+ * Mosaic components mounted directly in the host app's tree, rather than through clerk-js. They
+ * read Clerk via `@clerk/shared/react` hooks, so a `ClerkProvider` above them is all they need.
+ *
+ * Pair with the stylesheet, which carries the design tokens and every component rule:
+ *
+ * ```css
+ * @import '@clerk/react/experimental/mosaic/styles.css' layer(clerk);
+ * ```
+ *
+ * @experimental The surface and the components behind it are subject to change.
+ */
+export { UserButton } from '@clerk/ui/experimental/mosaic';
+export type { UserButtonProps } from '@clerk/ui/experimental/mosaic';

packages/react/tsdown.config.mts

@@ -63,6 +63,7 @@ export default defineConfig((overrideOptions: Options) => {
       internal: 'src/internal.ts',
       errors: 'src/errors.ts',
       experimental: 'src/experimental.ts',
+      'experimental/mosaic': 'src/experimental/mosaic.ts',
       legacy: 'src/legacy.ts',
       types: 'src/types/index.ts',
     },

packages/swingset/src/stories/menu.component.mdx

@@ -120,10 +120,10 @@ const [open, setOpen] = useState(false);
 Unlike the slot-recipe components, the Mosaic menu is themed with **StyleX**. Each styled part
 carries a stable `.cl-<slot>` class (the slots above) alongside the StyleX atoms. Consumers never
 target the hashed atomic classes — override by targeting the `.cl-*` slot from a CSS layer that wins
-over `@clerk/ui/styles.css`:
+over `@clerk/ui/experimental/mosaic/styles.css`:
 
 ```css
-@import '@clerk/ui/styles.css' layer(components);
+@import '@clerk/ui/experimental/mosaic/styles.css' layer(components);
 
 @layer overrides {
   .cl-menu-popup {

packages/swingset/src/stories/popover.component.mdx

@@ -189,10 +189,10 @@ them through your own typography (`Heading`, `Text`) inside the surface.
 Unlike the slot-recipe components, the Mosaic popover is themed with **StyleX**. Each styled part
 carries a stable `.cl-<slot>` class (the slots in the table above) alongside the StyleX atoms.
 Consumers never target the hashed atomic classes — override by targeting the `.cl-*` slot from a
-CSS layer that wins over `@clerk/ui/styles.css`:
+CSS layer that wins over `@clerk/ui/experimental/mosaic/styles.css`:
 
 ```css
-@import '@clerk/ui/styles.css' layer(components);
+@import '@clerk/ui/experimental/mosaic/styles.css' layer(components);
 
 @layer overrides {
   .cl-popover-popup[data-size='lg'] {

packages/ui/package.json

@@ -57,7 +57,12 @@
       "default": "./dist/experimental/index.js"
     },
     "./themes/shadcn.css": "./dist/themes/shadcn.css",
-    "./styles.css": {
+    "./experimental/mosaic": {
+      "types": "./dist-mosaic/index.d.ts",
+      "import": "./dist-mosaic/index.js",
+      "default": "./dist-mosaic/index.js"
+    },
+    "./experimental/mosaic/styles.css": {
       "types": "./styles.css.d.ts",
       "default": "./dist-mosaic/styles.css"
     },
@@ -81,14 +86,15 @@
     "register"
   ],
   "scripts": {
-    "build": "pnpm build:umd && pnpm build:esm && pnpm build:mosaic && pnpm check:no-rhc && pnpm type-check",
+    "build": "pnpm build:umd && pnpm build:esm && pnpm build:mosaic && pnpm check:no-rhc && pnpm check:no-emotion && pnpm type-check",
     "build:analyze": "rspack build --config rspack.config.js --env production --env analyze",
     "build:esm": "tsdown",
     "build:mosaic": "tsdown --config tsdown.mosaic.config.mts",
     "build:rsdoctor": "RSDOCTOR=true rspack build --config rspack.config.js --env production",
     "build:umd": "rspack build --config rspack.config.js --env production",
     "bundlewatch": "FORCE_COLOR=1 bundlewatch --config bundlewatch.config.json",
     "bundlewatch:fix": "node bundlewatch-fix.mjs",
+    "check:no-emotion": "node scripts/check-mosaic-emotion-free.mjs",
     "check:no-rhc": "node ../../scripts/search-for-rhc.mjs directory dist/no-rhc",
     "clean": "rimraf ./dist",
     "dev": "rspack serve --config rspack.config.js",
@@ -107,6 +113,7 @@
     "type-check": "tsc --noEmit"
   },
   "dependencies": {
+    "@clerk/headless": "workspace:^",
     "@clerk/localizations": "workspace:^",
     "@clerk/shared": "workspace:^",
     "@emotion/cache": "11.11.0",
@@ -126,7 +133,6 @@
     "qrcode.react": "4.2.0"
   },
   "devDependencies": {
-    "@clerk/headless": "workspace:^",
     "@floating-ui/react-dom": "^2.1.8",
     "@rsdoctor/rspack-plugin": "^1.5.9",
     "@rspack/cli": "catalog:rspack",