What this fixes

astryx swizzle <Component> copies a component's raw StyleX source into your app. That source needs a build-time StyleX compiler to produce atomic CSS — but nothing in the CLI output or docs said so, and there was no framework-specific setup guidance. Result: a freshly swizzled component compiles but renders unstyled, with no error, and it's non-obvious why. Fixes #3373.

Changes

1. Post-copy CLI note (only when the swizzled source actually uses StyleX). The copy loop now detects @stylexjs/stylex usage and, for StyleX components, prints:

⚠ These components use StyleX and require a StyleX compiler in your build.
  Without one they render unstyled (no error). See setup per framework:
  npx astryx docs styling
  Next.js note: the StyleX Babel plugin disables SWC and breaks next/font —
  use an SWC-based StyleX transform instead (covered in the guide).

Components with no StyleX get no note (verified by a negative test). The --json payload also gains a usesStyleX boolean for machine consumers.

2. Docs: a "StyleX Build Setup" section in astryx docs styling. The issue noted that grepping the docs for babel, swc, next.config, compiler, transform, or plugin returned nothing. The new section covers:

• Why swizzled components need a compiler (and that consuming the published package does not).
• A per-bundler table (Webpack, Vite/Rollup, Babel, Next.js).
• The Next.js App Router sharp edge: the StyleX Babel plugin disables SWC, which breaks next/font — so an SWC-based transform (e.g. the community @stylexswc/nextjs-plugin) is the working path, with a next.config example.
• A pointer to the working reference app apps/example-nextjs-stylex in the repo.
• The clarification that pure theming (defineTheme + astryx theme build) needs no StyleX compiler.

Why point at astryx docs styling rather than a wiki page

The issue mentioned astryx docs swizzle, but there is no swizzle docs topic, and no StyleX-setup wiki page exists yet. Rather than invent a URL, this puts the setup content in the existing styling doc (which the issue explicitly named as a gap) and points the CLI note there.

Verification

• Ran astryx swizzle Button in the monorepo: the StyleX note prints with the Next.js caveat and the astryx docs styling pointer.
• Ran astryx docs styling: the "StyleX Build Setup" section renders with the table, the Next.js note, and the next.config example.
• New tests in swizzle.routing.test.mjs: a StyleX component reports usesStyleX: true and prints the note (asserting the compiler requirement, the unstyled symptom, the next/font caveat, and the docs pointer); a non-StyleX component reports usesStyleX: false and prints no note.
• All existing swizzle tests (18 total across routing/path-safety/unit) pass; ESLint clean.