Deadline JSON formatting: avoid changing signed payloads

When formatting JSON under a deadline, save the original and check whether exact bytes matter. A signed or hashed payload can fail after harmless-looking whitespace changes. For ordinary data, format a copy, parse it, and compare values and types with the source. Review duplicate keys and critical fields such as IDs and endpoints. Do not mistake a clean pretty-print for schema validation. If the receiver expects a specific shape, run that check separately before sending.