VALIDATION-PLANES-11: Frontmatter enum, format, and bounds

What it demonstrates

Zod enum/date/min refinements over frontmatter surface as positioned frontmatter-plane findings.

Builds on: VALIDATION-PLANES-10: Cross into content: a one-field frontmatter schema

How it’s done

A TypeScript program against the library API; inline comments show the resulting values and behavior.

const c = contract({
  frontmatter: z.strictObject({
    id: z.string().min(1),
    status: z.enum(["open", "closed"]),
    created: z.string().date(),
  }),
});
// status: "bogus" -> frontmatter/enum at the status line
// an unexpected key -> frontmatter/unknown-key (strictObject)

Surfaces exercised

• z.enum() / z.string().date() / .min() over frontmatter
• z.strictObject() -> frontmatter/unknown-key (src/core/content.ts matchFrontmatter)
• frontmatter/enum (src/core/content.ts frontmatterIdFor)