//! Backend-agnostic staging writer trait.
//!
//! Synchronous enqueue (mpsc channel push) — zero DB, zero async.
//! Backend-specific flush: PG uses UNNEST INSERT, KVrocks uses XADD.
use crateResult;
/// High-throughput staging writer.
///
/// `enqueue()` is synchronous (mpsc push) — no async, no DB.
/// A background task handles batch flushing to the backend.