Updates editable profile fields on an existing candidate within a position, and returns the full updated candidate object.

This is a partial update — include only the fields you want to change. Only a fixed set of properties is accepted (name, email_address, phone_number, summary, source, headline, tags, address, social_profiles, custom_attributes, cover_letter); any other properties sent are silently ignored. email_address must be a valid email, tags must be an array, and each social_profiles key must be a supported network name with a valid URL value.