Repository layout

skin.json                skin registration, ResourceLoader, hooks
includes/
  SkinChroma.php         extends SkinMustache; injects site name/logo/search/edit data
  Hooks.php              Preferences fields, body data-* attributes
templates/skin.mustache  body-only Mustache template
resources/
  styles/tokens.css      generated MD3 tokens (light/dark/auto)
  styles/tokens-presets.css
  styles/base.css        layout and components
  styles/extensions.css  extension / special-page overrides
  styles/codex-bridge.css
  scripts/chroma.js      drawer, theme, layout, reading mode, scroll-spy, snackbar
i18n/                    en / qqq / zh-hans / zh-hant
tools/                   token and preset generators

Rendering flow

1. MediaWiki calls SkinChroma::getTemplateData();
2. SkinChroma adds sitename, link-search, has-logo, is-editable and link-edit;
3. templates/skin.mustache outputs body content only; <head> belongs to MediaWiki core;
4. Hooks::onOutputPageBodyAttributes() writes user preferences as data-chroma-*;
5. resources/scripts/chroma.js only provides progressive enhancement.

Do not

• output <html>, <head> or <body> from the template;
• put modules with dependencies in the skin styles option (ClientHtml drops them);
• hard-code colors instead of --md-sys-*;
• merge requires / menus across branches.