Form Validation Logic

Help me design validation for a {{form_type}} form. Cover the rules per field, client-side validation for fast feedback and server-side validation for security (never trust the client), helpful inline error messages, when to validate (on blur, on submit), handling async validation like uniqueness checks, accessibility for errors, and a single source of truth for the rules to avoid client and server drifting apart. Note that client validation is for UX and server validation is for safety, and the mistake of relying only on the client. Stack: {{stack}}.