Function has_parquet_metadata 

pub(crate) async fn has_parquet_metadata(
    cache: &DiskCache,
    cache_key: &str,
) -> bool

Whether the Parquet metadata header is cached for cache_key.

The cheap half of “is this replayable”: the header is a few hundred bytes, where the geometry blob is the whole model. The hash-only stream probe (#3901) asks this, plus has_current_data_model, BEFORE it takes an admission slot, so the common miss (a file the server has never seen) is answered by two small reads rather than by charging a parse slot for a disk lookup. check_cache asks it too, because its hit sends the client to a fetch that needs the header (#4675). It is a pre-filter, never the decision: try_cached_replay still makes that, and a metadata entry present here with no geometry beside it falls through to the same 404.