Shadcn Guideline: Form — Display form messages. Description: Use FormMessage for validation error display. Do: FormMessage after FormControl. Don't: Custom error text without FormMessage. Good Example: <FormControl><Input/></FormControl><FormMessage/>. Bad Example: <Input/>{error && <span>{error}</span>}. Severity: Medium. Docs: https://ui.shadcn.com/docs/components/form.