kmp-adapter-embedded

The embedded-edition storage adapters of KMP by Underpass, the Kernel Memory Protocol kernel.

One EmbeddedKernelStore opens one data directory — a FORMAT_VERSION marker next to store/ — and implements every persistence port the kernel needs: graph reads over materialized adjacency, node detail, the append-only context event log, projection runtime state, snapshots and quality telemetry. No server, no cluster, no daemon.

Two engines, one seam

The ports are written once against a small storage seam; the engine behind it is chosen when the directory is created and recorded in FORMAT_VERSION, so a store is never reopened by the wrong one.

redb is pure Rust, one file, one process: the default binary carries no C toolchain and no store you already have changes. SQLite is the opt-in for the case redb cannot serve — two agent hosts open at once, Claude Code and Codex CLI on the same project — where readers never block the writer and a second writer waits for the commit lock instead of being refused. Both engines pass the same conformance suite, the same kill -9 recovery test, and the SQLite engine additionally passes a two-process, no-lost-events scenario that redb is asserted to fail. See ADR-018.

A binary built without the feature still recognises a SQLite store and refuses it by name, saying which feature to enable; a binary older than the layout refuses it as "newer than this binary supports". Neither ever opens an empty store beside it.

What durability means here

Commits are fsync-durable on both engines (redb immediate durability; SQLite synchronous=FULL in WAL), so the crash contract is explicit: nothing is lost beyond the in-flight event, and replay applies nothing twice.

Not a special case

The observable semantics are pinned by the conformance suite that also certifies the in-memory store and the Neo4j / Valkey adapters. A store that passes it behaves like the others or it does not ship.

License

Apache-2.0.