rotary (rx4) — the agent harness engine

Pure agent harness engine. Models write; rotary gives them tools, memory, loops, permissions, sessions, and control planes.

Install

Library hosts should disable crate defaults and name only the features they need:

cargo add rx4 --no-default-features --features builtin-tools,providers

The rx4 binary is gated on the cli feature. A bare cargo install rx4 does not produce the binary:

cargo install rx4 --features cli,ipc,providers,builtin-tools,mcp

See docs/INSTALL.md for Homebrew notes and the full feature list.

Quick start

use rx4::{Agent, Scope, ToolRegistry, register_builtin_tools};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut agent = Agent::new();
    let mut tools = ToolRegistry::new();
    register_builtin_tools(&mut tools);
    agent.set_tools(tools);
    agent.set_scope(Scope::Coding);
    agent.prompt("fix the failing test").await?;
    Ok(())
}

Docs

Hashline, prewalk, AVO

The engine owns the tagged edit protocol (rx4::hashline), the one-way investigate→smol switch (rx4::prewalk, RX4_SMOL_MODEL), and AVO helpers (rx4::avo: P_t, two-part f, commit-if-better, stall). Hosts enable them; they should not fork the protocol. See docs/HARNESS.md.

Opt-in autoresearch

• Documentation index
• Hosting guide
• telekinesis — CLI/TUI product host
• apollo — AI agent host

License

MPL-2.0