Function record_series_metadata 

fn record_series_metadata(
    index: &mut SemanticIndexes,
    symbols: &[&str],
    series_metadata: &Metadata,
    prom_ctx: &PromCtx,
    table_name: &str,
) -> Result<()>

Stamps the series’ inline metadata for the written table’s auto-create: an explicit metric type upgrades the table’s metadata quality to declared, UNSPECIFIED series keep the request-level inferred stamp, and units are canonicalised from OpenMetrics words to UCUM. Type and unit stamp independently, as OpenMetrics defines them. Help text is not persisted.

Every non-zero symbol reference is validated up front, independent of what ends up persisted: the spec requires all references to point into the symbol table.