Matt Pocock's Sandcastle: a 'software factory' for coding agents

Matt Pocock (@mattpocockuk) set out his plan for version 1 of Sandcastle, his open-source TypeScript toolkit for running coding agents in isolated sandboxes: each task gets its own copy of the code and ends in a pull request. The plan adds six built-in harnesses (including Claude Code and Codex), sandbox providers such as Daytona, Vercel and E2B, templates for Inngest and Trigger.dev, and human-in-the-loop checks over Slack or Discord, with each skill becoming a reusable step such as CodeReview() or ImplementSpec(). The toolkit is on GitHub today; the v1 features are a plan, not a release. In a separate post he floated the idea that agents may work best when the 'state' of an app lives in one place, which limits the ways they can go wrong; that's an opinion.

Why it mattersIf your team runs more than one coding agent, the pattern is the lesson: one sandbox per task, a pull request at the end, and a person approving it. Watch for v1 rather than building on the plan.

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