Concepts

Four concepts shape every Kairos analytic. Read them in order: the tick model and the consumption model define the wire-and-callback contract; the two contract pages justify the historical surface and the on-disk tick parquet schema.

Topic	Source of truth
TickEvent model	The variant set fed into every analytic.
Consuming events	The typed .on_event callback, the subscription handle, panic isolation.
The historical surface	Bounded-termination historical contract — three-mode delivery (live / historical / replay).
The tick parquet schema	Tick parquet schema — one columnar RecordBatch per file.

Reading order

Recommended order for a new integrator:

1. TickEvent model — what flows in.
2. Consuming events — what flows out, and how the callback receives it.
3. The historical surface — why historical and replay share the same output type as live.
4. The tick parquet schema — what a recorded dataset looks like on disk.