Built-in operator node types for GraphReFly.

Operators in this crate are specialized node types implemented directly against the Core protocol — they are not "user fns wrapped in nodes." A map operator's plumbing (dirty propagation, equals dedup, batch handling) runs entirely in Rust; only the user-supplied (T) -> U callback crosses the FFI boundary on each fire.

Status (Slice C-3, 2026-05-06)

Transform module: [map], [filter], [scan], [reduce], [distinct_until_changed], [pairwise] (Slice C-1, D009–D019). Combine module: [combine_latest], [merge], [with_latest_from] (Slice C-2, D020–D023). Flow module: [take], [skip], [take_while], [last], [last_with_default] + [first], [find], [element_at] sugar (Slice C-3, D024–D029). Per-operator state lives behind a generic OperatorScratch slot on NodeRecord (D026 — replaces the typed operator_state field used by Slices C-1 / C-2).

Module layout (planned)

• [transform] — map, filter, scan, reduce, distinctUntilChanged, pairwise (✅ Slice C-1)
• [combine] — combine, merge, withLatestFrom (✅ Slice C-2)
• [flow] — take, skip, takeWhile, last + first/find/element_at sugar (✅ Slice C-3)
• temporal — throttle, debounce, sample
• switching — switchMap, mergeMap, concatMap
• gating — valve, gate, budgetGate, policyGate
• resilience — retry, circuitBreaker, timeout, fallback, rateLimiter, tokenBucket

Layering

This crate depends on graphrefly-core only (per the user-direction constraint that operators do not depend on graphrefly-graph). Operator factories accept &Core directly. User callbacks travel through the [OperatorBinding] super-trait of BindingBoundary, which the binding crate (e.g., a TestOperatorBinding for tests, the napi-rs / pyo3 bindings in production) implements.