What is sdk-js?

The sdk-js project lets you build "capsules" for Astrid OS using JavaScript or TypeScript. Capsules are modular programs that run inside Astrid, think of them as installable plugins or services that expose tools, handle requests, and talk to each other. If you've ever written a Node app and wanted it to feel like a native system component rather than a script running in the background, this is that kind of experience. At a high level, you write a TypeScript class and decorate it with annotations like @capsule or @tool to declare what your capsule does. The build pipeline then compiles your code, bundles it with the SDK, and packages everything into a .capsule archive that the Astrid kernel can install and run. The result is a WebAssembly binary, but you don't have to think about that, you just write JavaScript-flavored code and let the tooling handle the rest. The SDK provides familiar-feeling modules for filesystem access, networking, logging, key-value storage, inter-capsule messaging, and more, so it reads more like writing against Node's standard library than learning an entirely new platform. This is aimed at developers building tools or services for Astrid OS who prefer JavaScript over Rust. A concrete example from the README: you can create a capsule that exposes a "greet" tool, install it with astrid capsule install, and the kernel handles the rest. The same capsule lifecycle (install, run, upgrade) applies regardless of language. There's a companion Rust SDK that targets the same contracts, so a team could prototype in JS and port to Rust later without the kernel caring which language produced the binary. The main tradeoff is binary size. JavaScript capsules come out around 11 MB (3.5 MB compressed), mostly due to the embedded JS runtime, while Rust capsules are roughly 200 KB. For long-running services that load once and stay active, that's probably fine. For tight, resource-constrained scenarios, Rust is the better call. The project is currently in alpha, the end-to-end flow works, but it's still early.