Add Keystatic CMS integration

[VibratingKoala]

Requirement

Add Keystatic as a CMS option alongside the existing microCMS, so users can scaffold an Astro project with a Git-based, locally-editable CMS out of the box.

Scope for the first iteration:

• Bases: all Astro bases (astro, astro-react, astro-vue). Excluded from Nuxt and Vite (Keystatic has no integration for them).
• Storage: generate storage: { kind: 'local' } by default — zero external setup, works on first dev run. Include a commented github block + README note so users can switch when deploying.
• React renderer: Keystatic's admin UI is React-based, so auto-inject @astrojs/react (+ react/react-dom) for astro and astro-vue bases where it isn't already present.

Implementation notes (details and test plan to be documented in the PR):

• Re-key CMS templates by provider: templates/cms/{cms}/{group} (move existing microCMS templates under templates/cms/microcms/...).
• Add the keystatic entry to cms[] in registry.json with excludeGroups: ["nuxt", "vite"] (already enforced by the wizard).
• Conditionally inject Keystatic + React + output: 'hybrid' into astro.config.mjs.tmpl.
• Add the React cross-cutting rule in packagejson.go; update the --cms flag help and add CMS validation in cmd/create.go.
• Add keystatic.config.ts.tmpl (local storage, sample collection) under templates/cms/keystatic/astro/.

Open item to resolve during implementation: Astro output: 'hybrid' requires an adapter to build; reconcile the default (@astrojs/node) with the existing Cloudflare deploy option.

Notes

Related Issues

1. Add Shadcn component integration #17 (Shadcn integration — sibling "integration" feature, no dependency)

[VibratingKoala]

Viability review

Verdict: viable, but two assumptions in the original write-up were wrong and need correcting before implementation. The repo pins Astro ^6.1.3 and React ^19.2.4, which changes the details materially.

Verified facts (June 2026)

• Astro 6 + React 19 are supported by Keystatic, but only on the latest releases:

  • @keystatic/astro@5.1.0 — peerDeps astro: 2 || 3 || 4 || 5 || 6, react: ^18.2.0 || ^19.0.0
  • @keystatic/core@0.5.50 — peerDeps react: ^18.2.0 || ^19.0.0
  • Astro 6 support landed via Support Astro 6 Thinkmill/keystatic#1534, published ~2026-05-27 (issue #1515 closed COMPLETED). React 19 supported since #1374 (closed 2025-02-11).
  • ⚠️ Use these versions, not the ^5.0.4 / ^0.5.47 in the original notes — those predate Astro 6 support.

• output: 'hybrid' no longer exists (removed in Astro 5; folded into static). Official Astro + Keystatic guide uses:

  import react from '@astrojs/react'
  import keystatic from '@keystatic/astro'
  export default defineConfig({
    integrations: [react(), keystatic()],
    output: 'static',
  })

• An adapter is required. Keystatic's /keystatic admin UI and /api/keystatic/* routes are server-rendered on demand, so an adapter must be configured even though output is static. This was under-weighted originally and is the main added scope.

Corrected scope / decisions

1. Versions: @keystatic/astro@^5.1.0, @keystatic/core@^0.5.50.
2. astro.config: output: 'static', integrations: [react(), keystatic(), ...] — drop the hybrid idea.
3. Adapter (the real decision): Keystatic needs one. Options:
   • Default to @astrojs/node (mode standalone) when no deploy target is chosen — works for local dev + admin out of the box.
   • When the existing Cloudflare deploy option is also selected, use @astrojs/cloudflare instead (Keystatic + CF Pages/Workers is a known-trickier combo — may scope as "not supported in v1" if it fights us).
   • This makes adapter selection a cross-cutting rule (CMS × deploy target), not a flat package add.
4. Markdoc: the official guide also adds @astrojs/markdoc for document fields. Keep the sample collection simple (avoid markdoc fields) to skip this dep in v1, or include it if we want a rich-text field.

Risks

• Freshness: Astro 6 support is ~1 month old. Contributors on #1515 report editor dropdowns and the "set a link" modal misbehaving on the very latest builds (some downgraded 0.5.50 → 0.5.49). Recommend pinning a known-good version and smoke-testing the admin UI as part of the PR test plan.
• Adapter × deploy interaction is the most likely source of breakage — needs an explicit cross-cutting rule and a test.

Bottom line

Buildable on the current Astro 6 / React 19 stack with the corrected versions and an adapter. The template re-keying (templates/cms/{cms}/{group}), registry entry, and React injection from the original plan all still hold.