Built-in Rails facility (parameter filter) that, given a configured list of regular expressions or strings, redacts matching attributes from a payload. Callaghan pipes every payload destined for the observability vendor through a parameter filter in one central place — avoiding sprinkling filters across the codebase — to prevent leaking email addresses, credit card numbers, and other PII over the wire. Notes this is under-documented and complements vendor-side redaction (which should be a belt-and-braces, not the primary defense).