Docker Sandbox

Commands classified as forbidden or restricted by the Dual-Tool Evaluator are executed in hardened Docker containers for isolation.

When Sandbox Is Used

The sandbox is invoked when the evaluator classifies a command as:

• Forbidden - Matches the forbidden_commands list
• Restricted - Targets a path in the restricted_paths list
• Unknown tool - Defense-in-depth for unrecognized tool names

Container Configuration

Each sandbox execution creates a short-lived container with aggressive hardening:

Setting	Value	Purpose
network_disabled	True	No network access
mem_limit	256m	Memory ceiling
CPU	50%	CPU limit
pids_limit	100	Process count limit
read_only	True	Read-only root filesystem
tmpfs	/tmp:64M	Small writable scratch space
security_opt	no-new-privileges	Prevent privilege escalation
user	nobody	Non-root user
cap_drop	["ALL"]	Drop all Linux capabilities
labels	{"contop.sandbox": "ephemeral"}	Container identification

Docker Desktop Auto-Start

The server checks platform-specific paths for Docker Desktop and starts it if needed:

• Polls the Docker daemon every 2 seconds
• Waits up to 45 seconds for Docker to become available
• Reports status to the mobile UI via real-time status callback messages

Fallback Without Docker

When Docker is unavailable (not installed or failed to start), the sandbox falls back to a restricted host subprocess:

Setting	Value
auto_confirm	False (always requires confirmation)
timeout	min(timeout_s, 10) - 10 seconds maximum
Output limit	50 KB (standard max_output_bytes default)

This fallback is intentionally restrictive - it prevents unattended execution of potentially dangerous commands without Docker's isolation guarantees.

Environment Sanitization

The sandbox container does not inherit the host's environment variables. Sensitive variables (API keys, tokens) are never passed to the container.

Base Image

The Docker container uses python:3.12-slim as its base image. The image is pulled on first use if not present locally.

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Related: Dual-Tool Evaluator · Core Tools · Security Overview