Collections must have a loader defined — Astro 6 removed type: 'content' / type: 'data' collections

// before (Astro <= 5 legacy)
import { defineCollection, z } from 'astro:content'
const blog = defineCollection({ type: 'content', schema: z.object({ title: z.string() }) })
const authors = defineCollection({ type: 'data', schema: z.object({ name: z.string() }) })

// after (Astro 6, src/content.config.ts)
import { defineCollection } from 'astro:content'
import { glob, file } from 'astro/loaders'
import { z } from 'astro/zod'
const blog = defineCollection({
  loader: glob({ pattern: '**/[^_]*.{md,mdx}', base: './src/content/blog' }),
  schema: z.object({ title: z.string() }),
})
const authors = defineCollection({
  loader: glob({ pattern: '**/*.json', base: './src/content/authors' }),
  schema: z.object({ name: z.string() }),
})
export const collections = { blog, authors }

Astro 6 also uses Zod 4. Use z.email() instead of z.string().email(), and { error: '...' } instead of { message: '...' }. Importing z from astro:content is deprecated; use astro/zod.