The Memory — Tiers of Truth

Reads are answered from the nearest tier that can tell the truth. EchoStore is a declared near-cache: the ecc:{table}:{id} keyspace, values framed version<>value, an L1 of ETS tables over the shared L2 Valkey. The L1 is :public on purpose — a hit is a caller-side lookup that never enters the owner process — and the chapter names the contrast once, precisely: BCS systems keep :private tables to enforce the gate; the cache publishes its table to serve the read path. Two disciplines, one primitive, both deliberate — naming ETS without its discipline is the banned move; always say which.

Coherence is a message about a name: twenty-nine bytes, id:version, exactly two identities and a separator. In :tracking mode the store arms RESP3 client tracking — CLIENT TRACKING ON BCAST over the table's prefix, on a dedicated push connection — and an invalidation is one :ets.delete of one L1 row; the L2 is never touched by the push. Newer-wins is decided by mint order: the snowflake in the id is the only clock the protocol needs. Beneath it all, the journal — SQLite in WAL mode, a transactional outbox — records intents and replays the writes the network dropped, deduplicated by their recorded job ids at bus admission. The workshop writes through L2, watches the push delete the row, and measures the staleness window — the paper's dial, held in one table.

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