Crate localharness 

localharness — Rust-native agent SDK for Gemini

Build production agents with streaming text, custom tools, safety policies, and background triggers — all from a single cargo add, zero external binaries.

Quick start

use localharness::{Agent, GeminiAgentConfig};

let cfg = GeminiAgentConfig::new(std::env::var("GEMINI_API_KEY").unwrap())
    .with_system_instructions("You are a concise code reviewer.");

let agent = Agent::start_gemini(cfg).await?;
let response = agent.chat("What is 2+2?").await?;
println!("{}", response.text().await?);
agent.shutdown().await?;

Layers

Layer	Type	Purpose
1	Agent	High-level facade: connect, chat, shutdown.
2	Conversation / ChatResponse	Stateful session, multi-cursor streams.
3	connections::Connection	Transport abstraction.
aux	Filesystem	What the 6 fs-shaped built-in tools call into; swap the impl to target OPFS, an in-memory FS, etc.

Re-exports

pub use agent::Agent;

pub use agent::AgentConfig;

pub use agent::GeminiAgentConfig;

pub use backends::gemini::decode_transcript_bytes;

pub use backends::gemini::GeminiBackendConfig;

pub use backends::gemini::GeminiConnection;

pub use backends::gemini::GeminiConnectionStrategy;

pub use backends::mcp::McpBridge;

pub use backends::mcp::McpClient;

pub use backends::mcp::McpToolDecl;

pub use connections::Connection;

pub use connections::ConnectionStrategy;

pub use content::Content;

pub use content::Media;

pub use content::MediaKind;

pub use content::Part;

pub use conversation::ChatCursor;

pub use conversation::ChatResponse;

pub use conversation::Conversation;

pub use error::Error;

pub use error::Result;

pub use filesystem::DirEntry;

pub use filesystem::EntryKind;

pub use filesystem::Filesystem;

pub use filesystem::Metadata;

pub use filesystem::SharedFilesystem;

pub use filesystem::WalkEntry;

pub use filesystem::NativeFilesystem;

pub use hooks::HookContext;

pub use hooks::HookRunner;

pub use hooks::OnSessionEndHook;

pub use hooks::OnSessionStartHook;

pub use hooks::OperationContext;

pub use hooks::PostToolCallHook;

pub use hooks::PostTurnHook;

pub use hooks::PreToolCallDecideHook;

pub use hooks::PreTurnHook;

pub use hooks::SessionContext;

pub use hooks::TurnContext;

pub use policy::allow_all;

pub use policy::deny_all;

pub use policy::enforce;

pub use policy::evaluate;

pub use policy::is_path_in_workspace;

pub use policy::secure_normalize_path;

pub use policy::workspace_only;

pub use policy::AskUserHandler;

pub use policy::Decision;

pub use policy::Policy;

pub use policy::Predicate;

pub use tools::ClosureTool;

pub use tools::Tool;

pub use tools::ToolContext;

pub use tools::ToolRunner;

pub use triggers::every;

pub use triggers::Trigger;

pub use triggers::TriggerContext;

pub use triggers::TriggerRunner;

pub use types::BuiltinTool;

pub use types::CapabilitiesConfig;

pub use types::GeminiConfig;

pub use types::GenerationConfig;

pub use types::HookResult;

pub use types::ModelConfig;

pub use types::ModelEntry;

pub use types::Step;

pub use types::StepSource;

pub use types::StepStatus;

pub use types::StepTarget;

pub use types::StepType;

pub use types::StreamChunk;

pub use types::SystemInstructions;

pub use types::ThinkingLevel;

pub use types::ToolCall;

pub use types::ToolResult;

pub use types::TranscriptEntry;

pub use types::TranscriptRole;

pub use types::TriggerDelivery;

pub use types::UsageMetadata;

Modules

agent

Layer-1 agent facade: connect, chat, shutdown. Layer-1 Agent facade.

backends

Backend implementations (Gemini, MCP). Backend implementations of the Connection trait.

connections

Transport abstraction traits. Transport abstraction.

content

Multimodal input primitives (text, images, documents, audio, video). Multimodal input primitives.

conversation

Stateful conversation session with multi-cursor streaming. Stateful conversation session.

error

Typed error hierarchy. Typed error hierarchy for the SDK.

filesystem

Filesystem abstraction for built-in fs tools. Filesystem abstraction for the built-in fs tools.

hooks

Hook traits for observing and gating agent events. Hook traits and the runner that dispatches them.

policy

Declarative tool-execution policy engine. Declarative tool-execution policy engine.

rustlite

Rust-subset to wasm compiler.

tools

Custom tool registration and dispatch. Host-side custom tools.

triggers

Background triggers that push messages into the agent. Background triggers — fire-and-forget tasks that push messages into the agent. Each trigger runs in its own tokio task; the runner owns the task handles and aborts them on shutdown.

types

Public boundary types (steps, tool calls, usage, config, etc.). Public boundary types for the SDK.