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Runtime

The everruns-runtime crate runs an Everruns harness entirely inside your own Rust process . There is no PostgreSQL, no control-plane server, and no worker boundary — just the harness, your capabilities, and your code.

It is the Rust-native counterpart to the SDKs: where the SDKs talk to a running Everruns server over HTTP, the runtime is the engine, linked straight into your binary.

Use the runtime when you want to:

Run a harness in-process with no external services

Register your own capabilities, drivers, and tools

Provide your own backend stores (files, messages, sessions, …)

Inspect the assembled turn context before execution

It ships in-memory by default , so the smallest useful host is a single build().await? away.

Install

Requires Rust 1.94+ (edition 2024).

Terminal windowcargo add everruns-runtime

The crate also depends on everruns-core for shared types (capabilities, drivers, models):

Terminal windowcargo add everruns-core

Quickstart

Build an in-process runtime with an in-memory backend and a simulated LLM, then run a turn:

use everruns_core::{

CapabilityRegistry, DriverId, DriverRegistry, PlatformDefinition, ResolvedModel,

};

use everruns_core::llmsim_driver::LlmSimConfig;

use everruns_runtime::InProcessRuntimeBuilder;

let platform = PlatformDefinition::new(CapabilityRegistry::new(), DriverRegistry::new());

let runtime = InProcessRuntimeBuilder::new()

.platform_definition(platform)

.llm_sim(LlmSimConfig::fixed("hello from everruns-runtime"))

.default_model(ResolvedModel {

model: "llmsim-model".into(),

provider_type: DriverId::LlmSim,

api_key: Some("fake-key".into()),

base_url: None,

provider_metadata: None,

})

// .capability(...)

// .backends(...)

// .harness(...)

// .session(...)

.build()

.await?;

Swap llm_sim(...) for a real default_model (OpenAI, Anthropic, OpenRouter, Ollama, …) to talk to a live provider.

Inspect the turn context

load_context(session_id) returns the exact merged context the reason phase will use — before the first turn or after messages already exist:

let context = runtime.load_context(session_id).await?;

println!("messages = {}", context.messages.len());

println!("model = {}", context.runtime_agent.model);

println!("tools = {}", context.runtime_agent.tools.len());

The context bundles the harness chain, optional agent, session, filtered message history, resolved model, and the assembled RuntimeAgent. With no messages yet, context.messages is empty and model/locale resolution falls back to merged harness, agent, session, and platform defaults.

Execute-time hosts use everruns_core::assemble_turn_context(...) while inspection uses everruns_core::inspect_turn_context(...); both share the same assembly logic, so in-process and worker-backed behavior stay aligned.

Custom backends

The runtime ships in-memory defaults, but public extension traits let you supply your own stores:

| Trait | Backs |<br>|---|---|<br>| RuntimeHarnessStore | Harness definitions |<br>| RuntimeAgentStore | Agent configurations |<br>| RuntimeSessionStore | Sessions |<br>| RuntimeMessageStore | Message history |<br>| RuntimeFileStore | Session files |<br>| RuntimeProviderStore | LLM providers |<br>| EventBus | Emitted events (extends EventEmitter) |

Pass them through RuntimeBackends on the builder; any store you don’t override stays in-memory:

use everruns_runtime::{InProcessRuntimeBuilder, RuntimeBackends};

let runtime = InProcessRuntimeBuilder::new()

.backends(

RuntimeBackends::in_memory()

.with_file_store(my_file_store)

.with_message_store(my_message_store)

.with_event_bus(my_event_bus),

.build()

.await?;

The default in-memory EventBus retains emitted events for InProcessRuntime::events(); production buses inherit the default collected_events and return an empty Vec.

Local MCP servers

MCP server tools are first-class runtime tools. Local-process (stdio) MCP servers are gated behind the mcp-stdio feature, off by default so the hosted server/worker never compile stdio in:

Terminal windowcargo add everruns-runtime --features mcp-stdio

Built with the runtime

yolop — a minimal terminal coding agent built on everruns-runtime (codex/claude-code in spirit). It started as the coding-cli example below, promoted into a standalone, releasable project, and is where active development happens: interactive TUI, real-filesystem tools, a bash tool, multi-provider LLMs (OpenAI, Anthropic, Gemini, OpenRouter, Ollama), MCP servers (stdio + HTTP), resumable sessions, and Zed editor integration over ACP.

Terminal windowbrew install everruns/tap/yolop

# or

cargo install yolop --locked

examples/coding-cli — the in-tree reference embedder for the public crate: a single-binary coding agent with a ratatui TUI, real-filesystem tools on RealDiskFileStore, a custom bash tool, skills, and infinity-context trimming. It lives at the workspace edge and depends on the public crate exactly the way an external embedder would.

examples/weekend-concierge-host...