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.

backends

Backend implementations of the Connection trait.

connections

Transport abstraction.

content

Multimodal input primitives.

conversation

Stateful conversation session.

error

Typed error hierarchy for the SDK.

filesystem

Filesystem abstraction for the built-in fs tools.

hooks

Hook traits and the runner that dispatches them.

policy

Declarative tool-execution policy engine.

tools

Host-side custom tools.

triggers

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 for the SDK.