Sidecars: A low-latency trust boundary for Sandboxes | Modal Blog
Original excerpt
Simon Willison calls it the lethal trifecta : an agent with access to private data, exposure to untrusted content, and the ability to communicate externally can be tricked into leaking that data. A coding agent whose harness runs in its Sandbox has all three by default.
Context
Hosting the harness and the tool calls together is a security risk. The harness's credentials sit next to generated code, the agent can read untrusted content from the web, like packages and repos, and anything in the Sandbox can make network calls..