Prompt-to-PR: Add a Sitemap and robots.txt

SOP for adding a dynamic XML sitemap and robots.txt to a Next.js or Astro project — correct lastmod, priority, and crawl rules for production SEO.

Sitemaps and robots.txt are the first SEO primitives an agent touches, and they are frequently wrong — wrong lastmod format, missing Sitemap: directive in robots, or blocked pages inadvertently included. This playbook gets them right.

1. Requirement

Produce an XML sitemap covering all public routes (static + dynamic content from the database) and a robots.txt that blocks admin/API paths and references the sitemap. Works for both Next.js App Router and Astro; choose the correct approach for your framework.

2. First Prompt

Add a sitemap.xml and robots.txt to this project. Use the correct approach
for the framework detected below.

### If Next.js 14+:
1. Create `src/app/sitemap.ts` using the Next.js `MetadataRoute.Sitemap`
   return type. Include:
   - All static routes: /, /pricing, /blog, /about (hardcoded is fine).
   - All dynamic blog posts: fetch slugs from the DB using the existing
     query helper, return lastModified from the post's updatedAt field.
   - Use `process.env.NEXT_PUBLIC_APP_URL` as the base URL.
   - Correct W3C datetime format for lastModified (ISO 8601).
2. Create `src/app/robots.ts` using MetadataRoute.Robots.
   - Allow: all routes.
   - Disallow: /admin, /api, /dashboard.
   - Add `sitemap: process.env.NEXT_PUBLIC_APP_URL + "/sitemap.xml"`.

### If Astro:
1. Add `@astrojs/sitemap` integration. In astro.config.ts, add
   `sitemap({ filter: (page) => !page.includes("/admin") })` and set
   `site: process.env.SITE_URL`.
2. Create `public/robots.txt`:
   User-agent: *
   Disallow: /admin
   Disallow: /api
   Sitemap: <SITE_URL>/sitemap-index.xml

Do not create a custom sitemap endpoint if the integration handles it.
Do not block / or any public content pages.

3. Expected File Changes

### Next.js
src/app/sitemap.ts             (new — dynamic MetadataRoute.Sitemap)
src/app/robots.ts              (new — MetadataRoute.Robots)

### Astro
astro.config.ts                (add sitemap integration + filter)
public/robots.txt              (new)
.env.example                   (SITE_URL added if missing)

4. Review Checklist

Base URL comes from an env var — not hardcoded as http://localhost:3000.
lastModified is a JavaScript Date object (Next.js converts to ISO 8601) or already a valid ISO string — not "undefined" or missing.
/admin, /api, and /dashboard are in the Disallow list.
The Sitemap: directive in robots.txt uses an absolute URL.
Dynamic routes (blog posts) are included via a DB query, not just static routes.
The sitemap does not include 404, redirect, or noindex pages.
bun run build then curl /sitemap.xml returns valid XML (check with xmllint).

5. Test Commands

bun run build && bun run start
# or for Astro:
bun run build && bun run preview

# Validate sitemap XML
curl -s http://localhost:3000/sitemap.xml | xmllint --format - | head -40

# Confirm robots.txt
curl http://localhost:3000/robots.txt

# Confirm admin is disallowed and sitemap directive is present
grep -E "Disallow|Sitemap" <(curl -s http://localhost:3000/robots.txt)

# Google Rich Results / URL Inspection simulation
curl -A "Googlebot" http://localhost:3000/sitemap.xml -I

6. Common Failures

lastModified is "undefined" — post’s updatedAt field is null. Guard: lastModified: post.updatedAt ?? post.createdAt ?? new Date().
Sitemap returns 404 — src/app/sitemap.ts is missing or placed outside the app directory.
All routes disallowed — agent adds Disallow: / by mistake. Confirm only admin/API paths are blocked.
Sitemap: directive has relative URL — Google ignores it. Must be absolute: https://example.com/sitemap.xml.
Static sitemap only — agent hardcodes blog slugs instead of querying the DB. Confirm the sitemap function is async and fetches real data.

7. Fix Prompt

The sitemap.xml at /sitemap.xml includes every blog post with
lastModified "undefined" (rendered as the string).

Fix in src/app/sitemap.ts:
  const posts = await getBlogPosts();
  return posts.map((post) => ({
    url: `${BASE_URL}/blog/${post.slug}`,
    lastModified: post.updatedAt ?? post.createdAt ?? new Date(),
    changeFrequency: "weekly",
    priority: 0.8,
  }));

Ensure getBlogPosts() returns rows that include updatedAt and createdAt.

8. PR Description

## SEO: Add dynamic sitemap.xml and robots.txt

**Next.js**: `src/app/sitemap.ts` + `src/app/robots.ts` using built-in
`MetadataRoute` types. Sitemap includes static routes + all published blog
posts with correct `lastModified` timestamps from the DB.

**robots.txt** disallows `/admin`, `/api`, `/dashboard`; includes absolute
`Sitemap:` directive pointing to the generated `/sitemap.xml`.

Base URL read from `NEXT_PUBLIC_APP_URL` — no localhost URLs in production.