User submits form
    ↓
Frontend basic validation (required fields only)
    ↓
Backend authoritative validation (business rules + format checks)
    ↓
Service throws JSON error (preserving structure)
    ↓
Parent rethrows error (after logging/toast)
    ↓
Form component maps field → error message
    ↓
Input component highlights and displays message
    ↓
User fixes and resubmits

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