Historical builder

Preview (historical-mode Cargo feature). The historical namespace is the same per-analytic builder shape as the live namespace; .on_event fires the callback once per row over the bounded [start, end] result set and stops after every (contract, date) unit's terminal watermark. The bridge to the C ABI is a documented follow-up — .on_event on the historical namespace surfaces LinkError::HistoricalUnwired until the wiring lands. The accessor is opt-in so production FFI builds cannot reach a known fail-closed path.

Shape

// Cargo.toml:
//   kairos = { version = "0.1", features = ["historical-mode"] }

use kairos::{Client, GreeksRow};

let sub = client
    .historical(20251103, 20251107)   // YYYYMMDD inclusive
    .greeks(["QQQ"])
    .on_event(|row: &GreeksRow| {      // fires per row over the bounded set
        println!("delta={} gamma={}", row.delta, row.gamma);
    })?;

start and end are YYYYMMDD-encoded i32s per the engine's integer-time convention. Bare ticker symbols expand to the chain plus the underlying.

Bounded consumption

The chain is identical to the live namespace — the accessor, the universe argument, and the .on_event callback are the same. The only difference is that the callback fires over a finite result set rather than an open-ended live feed: on the historical namespace the stream ends after the last row, and the subscription becomes inactive on its own. The same typed <Camel>Row is delivered per emission in every mode.

See also

• Subscription builder — the same fluent shape on the live namespace.
• Consuming events — the callback delivery model.
• Client — the historical(start, end) namespace accessor.