Liminal

Conversation-native messaging built on beamr and haematite.

What it is

A messaging system where conversations — not individual messages — are the fundamental unit. Every channel is a lightweight BEAM process, every subscription is a monitor, and backpressure is supervision rather than configuration. Built for AI-agent coordination, where messages need to survive crashes and never get lost.

Status

v0.2.2. Core messaging, channels, schema validation, durable mailboxes, and the wire protocol are implemented and tested. Backpressure and predicate routing exist as tested subsystems not yet wired into the delivery path; the Aion integration is a set of protocol-level seams (worker registration, push dispatch, observability drain) consumed by the external aion crates. See docs/stack-review/ for the honest state map.

Install

The crate is published on crates.io as liminal-rs (the bare liminal name is taken by an unrelated crate), but it is imported as liminal. Use the package alias:

[dependencies]
liminal = { package = "liminal-rs", version = "0.2.2" }

use liminal::channel::ChannelHandle;
use liminal::conversation::ConversationHandle;

Crates

Crate (crates.io)	use as	Description
liminal-rs	liminal	Core library — channels, conversations, durability, routing, backpressure, protocol
liminal-sdk	liminal_sdk	Application-facing SDK traits for building liminal clients (no_std-capable)
liminal-server	liminal_server	Standalone server for the liminal bus

SDKs

• TypeScript (sdks/liminal-ts/) — browser and Node.js client
• Gleam (sdks/liminal-gleam/) — native BEAM client

Features

• Conversation-native — conversations have participants, lifecycles, and crash recovery; not just pipes.
• BEAM-native channels — every channel is a beamr process with crash isolation.
• Durable mailboxes — messages backed by haematite's content-addressed storage.
• Backpressure — slow consumers throttle producers; Accept / Defer / Reject are protocol primitives.
• Schema validation — messages validated against JSON Schema before delivery.
• Causal ordering & tracing — causal metadata and trace context carried on the envelope.
• Aion integration — workflow steps publish, subscribe, and coordinate through conversations.

Architecture

crates/liminal/src/
├── channel/       — pub/sub channels with schemas and supervision
├── conversation/  — first-class conversations with participants
├── durability/    — crash-safe message persistence (haematite-backed)
├── routing/       — message routing
├── pressure/      — backpressure / flow control
├── protocol/      — wire protocol
├── causal/        — causal ordering metadata
├── metrics/       — metrics registry
└── tracing/       — trace context propagation

Requirements

• Rust 1.85+
• Depends on beamr 0.11.0 and haematite 0.4.0

License

AGPL-3.0-only