Sandbox

Run agents in isolated environments — Local, Docker, E2B, Daytona, AgentBay

The sandbox system runs agent operations (file I/O, shell commands) in isolated environments instead of the host machine. Every Thread is bound to exactly one sandbox for its lifetime — this is an agent’s body.

Provider comparison

Provider	Isolation	Cost	Best for
Local	None (host passthrough)	Free	Development, trusted code
Docker	Container	Free	Testing, reproducible environments
Daytona	Cloud or self-hosted	Free (self-hosted)	Production, team environments
E2B	Cloud	$0.15/hr	Ephemeral tasks, CI
AgentBay	Alibaba Cloud	¥1/hr	China region

Session lifecycle

on_exit value	Behavior
pause	Pause on exit. Files, packages, processes preserved.
destroy	Kill on exit. Clean slate next time.

pause is the default — you keep everything across restarts.

Quick start

1. Configure a provider

   Go to Settings → Sandbox in the Web UI. Expand the provider card and fill in the required fields:

   Provider	Required
   Docker	Image name, mount path
   E2B	API key
   Daytona	API key, API URL
   AgentBay	API key

   Config is stored at ~/.leon/sandboxes/<provider>.json.

2. Start a sandboxed thread

   In the new conversation view, use the sandbox dropdown in the input area to select your provider. Send your first message — the Thread is now permanently bound to that sandbox.

3. Monitor resources

   Go to Resources (sidebar). Live CPU/RAM/disk metrics and a file browser per sandbox session.

Provider configuration

Docker

Requires Docker on the host. No API key needed.

{
  "provider": "docker",
  "docker": {
    "image": "python:3.12-slim",
    "mount_path": "/workspace"
  },
  "on_exit": "pause"
}

Field	Default	Description
docker.image	python:3.12-slim	Docker image
docker.mount_path	/workspace	Working directory inside container
on_exit	pause	pause or destroy

E2B

Cloud sandbox. Requires an E2B API key.

{
  "provider": "e2b",
  "e2b": {
    "api_key": "${E2B_API_KEY}",
    "template": "base",
    "cwd": "/home/user",
    "timeout": 300
  },
  "on_exit": "pause"
}

Install: uv sync --extra e2b

Daytona SaaS

{
  "provider": "daytona",
  "daytona": {
    "api_key": "${DAYTONA_API_KEY}",
    "api_url": "https://app.daytona.io/api",
    "cwd": "/home/daytona"
  },
  "on_exit": "pause"
}

Install: uv sync --extra daytona

Daytona self-hosted

{
  "provider": "daytona",
  "daytona": {
    "api_key": "${DAYTONA_API_KEY}",
    "api_url": "http://localhost:3986/api",
    "target": "us",
    "cwd": "/workspace"
  },
  "on_exit": "pause"
}

Self-hosted Daytona requires bash at /usr/bin/bash in both the runner and workspace images, runner on bridge network, and Daytona Proxy accessible on port 4000.

AgentBay

Alibaba Cloud sandbox for the China region.

{
  "provider": "agentbay",
  "agentbay": {
    "api_key": "${AGENTBAY_API_KEY}",
    "region_id": "ap-southeast-1",
    "context_path": "/home/wuying"
  },
  "on_exit": "pause"
}

Install: uv sync --extra sandbox

API key resolution

API keys are resolved in order:

1. Config file field (e2b.api_key, daytona.api_key, etc.)
2. Environment variable (E2B_API_KEY, DAYTONA_API_KEY, AGENTBAY_API_KEY)
3. ~/.leon/config.env

Session management

Web UI

From Resources:

• Unified grid of all sessions across all providers
• Click a session card → detail sheet with metrics and file browser
• Pause / Resume / Destroy via UI or API

API endpoints

Action	Endpoint
List sessions	GET /api/sandbox/sessions
Pause	POST /api/sandbox/sessions/{id}/pause?provider={type}
Resume	POST /api/sandbox/sessions/{id}/resume?provider={type}
Destroy	DELETE /api/sandbox/sessions/{id}?provider={type}
Metrics	GET /api/sandbox/sessions/{id}/metrics

Architecture

Middleware owns policy. The sandbox backend owns I/O. Swapping the backend changes where operations run without touching any middleware logic.

Sessions are tracked in SQLite (~/.leon/sandbox.db):

Table	Purpose
sandbox_leases	Lease lifecycle — provider, desired/observed state
sandbox_instances	Provider-side session IDs
abstract_terminals	Virtual terminals bound to Thread + lease
lease_resource_snapshots	CPU, memory, disk metrics