DECLARATIVE-YAML-04: Make fields optional, defaulted, or nullable

What it demonstrates

The three field wrappers — optional, default, nullable — applied over a base schema.

Builds on: DECLARATIVE-YAML-03: Bound and shape strings with min/max, pattern, format

How it’s done

The declarative YAML artifact, verbatim — no code required.

frontmatter:
  fields:
    last_reviewed: { type: string, format: date, optional: true }
    priority:      { type: number, default: 3 }
    archived_at:   { type: string, format: date, nullable: true }

Surfaces exercised

• compileSchema() wrappers: .optional()
• .default(value)
• .nullable()