Steps to reproduce the build-time type error — no code fix needed for this one

1. Edit src/content/docs/getting-started.md so its frontmatter reads:

     ---
     title: Getting Started
     order: "one"
     ---

   ("one" is a string, but the docs schema declares order: z.number().)

2. Run the dev server:

     npm run dev

3. Astro reports a real content validation error before the page
   even renders, naming the exact file and field, roughly:

     [InvalidContentEntryFrontmatterError] getting-started.md frontmatter
     does not match the collection schema.
     "order": Expected number, received string

Notes:
- This is the concrete, observable proof of Chapter 5's own central
  finding: the Zod schema isn't a suggestion or documentation — it's
  a real validation gate, enforced before the site ever builds or
  serves the affected page.
- Reverting order back to a real number (order: 1) clears the error
  immediately on the next save.