A sandbox is not a single package but a spectrum—Namespace, cgroups, seccomp, gVisor, and Firecracker stacked by trust boundary; local OS sandboxes bound blast radius, cloud microVMs bound multi-tenancy, and the choice hinges on trust and ops cost.
E2B combines Templates, Firecracker microVMs, and process, file, and network APIs into an agent execution layer. Its real selection advantage is preserving memory and processes across pause and resume, not merely providing another code interpreter.