// SPDX-License-Identifier: Apache-2.0
// Copyright (c) 2026 ReifyDB
//! Shared windowed-aggregation engine.
//!
//! Schema-agnostic core for both faces: the sdk drivers (static `Row` output)
//! and the flow Window/Aggregate operators (dynamic `Columns`/`RowShape`
//! output). [`accumulator`] holds the invertible [`accumulator::WindowAccumulator`]
//! trait and the reusable accumulator primitives; [`span`] holds the coordinate
//! machinery ([`span::Slot`], [`span::WindowSpan`]).