What's this about?
The SDK embeds policy-based containment into applications, with Windows process containers, Linux Bubblewrap and macOS Seatbelt plus additional backends. Filesystem, network and UI restrictions differ by backend; several VM options are experimental.
What exactly is sandbox?
An environment that limits what a program can access, like giving a contractor a key to one room rather than the whole building.
What's the community saying / why does it matter?
Willison’s post had 776 likes and described it as promising. Shared configuration can simplify agent tooling, but supported controls and isolation strength still need backend-specific evaluation.