Latest bar for a symbol+interval — the most-recent settled or forming bar

One OHLCV bar in the /v1/bars wire shape.

Prices are Decimal-as-string to match the existing /v1/prices/history contract and avoid float drift on the consumer side.

Metadata block in BarsResponse.

source_id is a PAGE-SCOPED provenance summary derived from the bars in this page — NOT a per-bar attribute. It equals the source_id of the first bar in the page, or "mixed" if the page spans multiple source_ids (e.g. a range that crosses from CSV history into a live Pyth feed). It is non-authoritative for mixed pages: consumers wanting per-bar provenance should wait for a future version that exposes bar.source_id per-bar. That per-bar field is a reserved future decision (flagged in the §9.4 public-surface audit); do NOT add it to the current Bar wire shape without a version bump.

Examples: 'csv_xau_15m_v1', 'csv_xau_rollup_v1', 'lse_gld', 'mixed'. Null when bars list is empty.