zu-backends 0.2.4

Zu sandbox backends and event sinks: local-docker, sqlite

zu-backends

Infrastructure adapters: the SandboxBackend port (provision and run a tier's environment) and the EventSink port (persist and query the event log). These are the durable/isolation seams the core defers behind a port.

Registered plugins

Sandbox backends (zu.backends)

Name	Class	Notes
local-docker	LocalDockerBackend	Runs a tier's container via the local Docker daemon. Network is disabled by default and enabled only for the render tier; scoped egress (allowlist / DNS-pinned) is the deferred egress-policy work. Needs the [docker] extra.

Event sinks (zu.sinks)

Name	Class	Notes
sqlite	SqliteSink	The durable canonical store: WAL, synchronous=FULL, busy_timeout, single writer, keyset streaming, idempotent append.
jsonl	JsonlSink	One JSON object per line — a greppable secondary/trace sink that log shippers tail.

The payload codec seam (zu_core.codec) lets a sink encrypt payloads at rest; an AES-256-GCM codec ships behind the optional [encryption] extra (zu_backends.encryption). Every sink links each event into its trace's tamper-evidence hash chain (zu_core.chain, ZU-AUDIT-1).

Upstream-conformance reference plugins

Dependency-light reference implementations of the conformance ports (spec: zu-upstream-conformance.md, trusted base: docs/TCB.md):

Kind	Name	Class	Notes
zu.channels	credential-broker	broker:CredentialBroker	A harness-owned Channel (ZU-NET-2): secret read inside the adapter, narrow verbs (mint/introspect) return a derived token, never the secret.
zu.backends	oop-launcher	oop_launcher:OutOfProcessLauncher	Runs a plugin (e.g. the broker) in a separate process/uid over the zu_core.rpc socket contract (ZU-NET-3 / ZU-CORE-3): a harness compromise yields the socket, not the secret.
zu.workload_identity	static	identity:StaticIdentity	Attestable identity (ZU-NET-4/5): HMAC-signed principal + optional attestation measurement; stdlib-only. mTLS/SPIFFE are follow-ons behind the same port.
zu.egress_enforcement	docker-internal-net, nftables	egress_enforce:*	Pluggable default-deny + DNS gating port (ZU-NET-1). The SandboxLauncher routes through it: pin the proxy by IP + gate the embedded resolver so DNS isn't a covert channel. ScriptedEnforcement proves swappability offline; nftables is the Linux-native mechanism; live behavior is validated under --run-docker.

broker.py's narrow verbs are the worked example for ZU-EXT-3 (many narrow typed ports, not one wide "send this request" proxy).

Extend

Implement the SandboxBackend or EventSink shape, register under zu.backends / zu.sinks, and add a deterministic test (inject a fake Docker client / use a temp DB path — no real daemon needed offline).

Tests

uv run pytest packages/zu-backends — offline.