Sandbox SDK 1.0 adds direct Durable Object control of containers

Sandbox SDK 1.0 is available, with each sandbox container controlled directly by an application's Durable Object through the container API. Developers can choose an image and instance size at startup, and deployments leave running sandboxes untouched. Snapshots in public beta can save sandbox files and launch the same sandbox or another one from the saved state. Classes can decide when sandboxes stop, run commands with streamed input and output, send signals, open terminals, and serve authenticated previews from sandbox ports. The package also offers file transfer, S3-compatible bucket mounts, and directory backups to R2 that can be restored in other sandboxes, including on newer images. Existing 0.x applications keep running, and the 0.x SDK receives bug and security fixes until 2026-12-31. Teams can migrate sandboxes in one deployment or incrementally beside a 0.x class; switching an existing class to the new policy is a one-way deployment.