Cloudflare Sandbox SDK vs Offscreen

Cloudflare Sandbox SDK

Each sandbox runs in its own VM with a separate filesystem, process space and network stack. No hosted API. You deploy and secure a Worker before an agent can call anything, and the starter has no auth.

Offscreen

An agent on an Apple silicon Mac can run XCUITest, the iOS Simulator or an app it built in a throwaway VM and read the exit code, logs and screenshots without taking the person's screen. The project is six days old at v0.0.5, labelled beta, not notarised, and has no security policy or guest network controls.

Cloudflare Sandbox SDK

1. Derive the sandbox ID from the authenticated user, as the docs advise. IDs aren't secrets
2. Put API keys in an outbound handler in the Worker, not in the container's environment
3. Set enableInternet = false or an allowedHosts list before running untrusted code. Internet access is on by default
4. Check that a restored backup has every directory you expect. Backups of 10 MB or more have open bugs
5. Start new projects on 1.0. The 0.x library only gets fixes until 31 December 2026

Offscreen

1. Read .offscreen.toml before running anything and use its project key and task names. Don't guess them
2. Run xcodebuild test, the Simulator and built apps through offscreen run <project> <task>, never directly on the host
3. Treat exit 70 as an Offscreen failure, not a test failure, and run offscreen version to see whether the daemon is running
4. Ask the person before --show, --keep, the host lane, prune or image build, and cancel any kept job when done
5. Read screenshots and .xcresult bundles from the directory offscreen artifacts <job> prints