chore: import upstream snapshot with attribution

showcase/shell-docs/README.md

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+# Shell Docs
+
+`showcase/shell-docs` is the Next.js app that builds and serves
+`docs.copilotkit.ai`. Author CopilotKit product documentation here, not in the retired
+top-level `docs/` app.
+
+## Run Locally
+
+Shell-docs is a standalone npm-based app. You do not need a root install just to run the
+docs app locally.
+
+```bash
+cd showcase/scripts
+npm install
+
+cd ../shell-docs
+npm install
+npm run dev
+```
+
+The local dev server runs on port `3003`.
+
+```text
+http://localhost:3003
+```
+
+The shell-docs npm lifecycle generates registry, demo-content, setup-content, and search
+data before `dev`, `build`, and `typecheck`.
+
+## Validate Changes
+
+Run these from `showcase/shell-docs`:
+
+```bash
+npm run build
+npm run typecheck
+npm run test
+```
+
+For repo-level CI parity, prefer Nx when a shell-docs target is available in the current
+checkout and root dependencies are installed. For normal shell-docs local development, the
+npm commands above are the canonical path.
+
+## Authoring Recipes
+
+### Showcase-Driven Framework Docs
+
+Showcase-driven frameworks use `docs_mode: generated`. The docs are assembled from showcase
+registry/generated data, demos, source regions, shared/root MDX, snippets, and sparse
+framework overrides.
+
+To update showcase-driven docs:
+
+1. Edit the showcase source of truth: manifests, demos, feature coverage, source regions, or
+   registry inputs.
+2. Edit shared/root MDX only when the change applies across generated frameworks.
+3. Add sparse framework overrides only for real framework-specific differences.
+4. Do not hand-edit generated files under `src/data/frameworks/`.
+5. Validate routes, sidebar state, search results, snippets, and framework switching.
+
+### Authored Framework Docs
+
+Authored frameworks use `docs_mode: authored`. The framework owns an MDX tree under
+`src/content/docs/integrations/<docsFolder>/` with a `meta.json` sidebar.
+
+To update authored docs:
+
+1. Check `getDocsFolder()` in `src/lib/registry.ts`; the URL slug and folder name may differ.
+2. Edit the MDX page under `src/content/docs/integrations/<docsFolder>/`.
+3. Update that folder's `meta.json` when adding, removing, or moving pages.
+4. Reuse shared snippets from `src/content/snippets/` when content should stay consistent
+   across frameworks.
+5. Validate the framework route, sidebar, search result, and any shared snippet render.
+
+### Reference Docs
+
+Edit API reference pages under `src/content/reference/`.
+
+The v2 reference does not use `meta.json`; navigation is generated by walking the tree and
+reading each page's `title` and `description` frontmatter. Only the legacy `reference/v1/`
+tree uses `meta.json`.
+
+### Snippets
+
+Reusable snippets live under `src/content/snippets/`. Snippets may be rendered by root docs,
+authored framework pages, and showcase-driven framework pages, so keep them general unless
+the path is intentionally framework-specific.
+
+### Frontend Applicability
+
+Frontend routes use page-level applicability metadata, independent from where the content is
+authored. A page can be authored MDX, showcase-generated content, mirrored protocol docs, or
+reference content and still be universal across frontends.
+
+Use the `frontend` field in page frontmatter or `meta.json` when a root doc should appear in
+non-React frontend docs:
+
+- `universal` — render the same page under `/<frontend>/...`.
+- `frontend-variant` — render only when a matching page exists under
+  `src/content/docs/frontends/<frontend>/...`.
+- `hide` — omit the page from frontend-scoped docs.
+
+Do not use "showcase-driven" as a proxy for frontend availability. Showcase derivation is an
+authoring/source detail; frontend applicability controls routing and sidebar inclusion.
+
+### AG-UI Mirrored Docs
+
+AG-UI protocol docs are authored upstream in `ag-ui-protocol/ag-ui`. The
+`src/content/ag-ui/` tree is a downstream mirror rendered on the CopilotKit docs host.
+Change AG-UI docs upstream first, then sync the mirror back into shell-docs.
+
+## Top-Level Docs Symlink
+
+The repository's top-level `docs/` path is a symlink to `showcase/shell-docs/` for
+contributor muscle memory. It is not a separate docs app. Do not recreate the old
+`docs/content/docs/` tree; author CopilotKit docs in `showcase/shell-docs/src/content/`.