Function mark_header_from_cache 

pub(crate) fn mark_header_from_cache(header: String) -> String

The stored X-IFC-Metadata header JSON, with stats.from_cache set to true.

The header is cached exactly as the live parse wrote it, and the live parse writes from_cache: false, because at that moment it was not. Replaying it verbatim therefore told every warm caller it had just been parsed: parseParquet() reported stats.from_cache === false on a cache hit (#5542), while GET /api/v1/cache/{key} and the JSON parse route both set the flag on theirs.

Works on the JSON value rather than a typed header so the flat and optimized headers (two different structs) share one rule, and so a field this build does not know about is carried through untouched. A header that is not a JSON object with a stats object is returned unchanged: that is what every replay path did before, and the flag is not this function’s reason to reject an entry.