Sandboxing AI-Generated Code: E2B vs Vercel Sandbox vs Modal vs Daytona in 2026

The first time I let an agent run its own code on a server I cared about, it deleted a directory it should not have been able to see. Nothing important. A tmp folder with a half-written script. But the agent had no business knowing the path existed, and the only reason it did was that I had given it a shell on a box that also had a copy of my dotfiles mounted in. The shell was supposed to be scoped. It was not. It was just a child process with a different working directory and a hopeful name.