A domain-neutral Agent runtime kernel implemented as a Rust framework.

Current boundary: Rust-first runtime kernel

The root workspace is now the Rust framework surface. It provides serializable runtime contracts, the reusable AgentRuntime kernel, and a native host helper that can run an Agent loop without Python.

Python code from the earlier framework has been moved to python/reference-mutsuki. Treat it as a reference and migration layer for plugin-host ideas, transport examples, and Python checks. It is no longer the root runtime implementation, but the name does not imply the code is deprecated or disposable.

The new Python backend kit lives in python/mutsuki-runtime-python. It mirrors the Rust contracts and provides an in-process Python backend host for strategy, operation, and resource lease experiments. It is not a standalone runtime and does not depend on the old reference package.

The long-term integration shape is:

Caller
  -> Rust Runtime Kernel
  -> Capability Backend

Callers can be Rust applications, Python plugin entries, HTTP services, CLIs, or other projects. Capability backends can be native Rust hosts, Python sidecars, or remote services. Python may act as both a runtime caller and a backend provider, but AgentRuntime remains the only runtime kernel: lifecycle, routing, inboxes, registry facts, resource governance, trace, and events stay in Rust.

• crates/mutsuki-runtime-contracts - pure serializable contracts: Agent, Envelope, ScopeRule, Operation / Source snapshots, trace, errors, and resource descriptors, plus runtime events.
• crates/mutsuki-runtime-core - runtime mechanics: lifecycle, inbox ticks, routing, operation registry, source registry, trace bookkeeping, event stream, election policy, trace closure checks, and resource lease governance.
• crates/mutsuki-runtime-host - native Rust host helper: in-memory operation/source backend for direct framework use, smoke tests, and a generic stdio JSONL backend adapter.
• python/mutsuki-runtime-python - optional Python backend kit: pure contract mirrors, in-process backend host, descriptor-only resource backend, stdio JSONL server, Python plugin/capability host fixtures, and documented future runtime-caller boundaries.

cargo test

Optional Python reference checks live under python/reference-mutsuki and should be run from that folder when intentionally working on that layer.

Python backend kit checks live under python/mutsuki-runtime-python:

uv run ruff check src tests
uv run pyright src tests
uv run pytest

• AGENTS.md - project constitution and hard rules
• plans/roadmap.md - current Rust-first target and gates
• plans/architecture.md - runtime direction and domain boundaries
• plans/engineering.md - workspace layout and implementation rules
• plans/contracts.md - internal contract surface
• plans/rust-python-runtime-boundary.md - Python reference boundary and optional host rules
• plans/python-backend-mvp.md - current Python backend kit MVP

See LICENSE.