codeSplitters: hosted deploys can't build a box whose native crates need Docker #351

Follow-up from #248 (PR #346). rustybuns build box cross-builds native/ crates in Docker when the box's arch isn't the build machine's (REFERENCE.md, "Rust crates build in Docker off Linux"). The hosted deploy container (deploy-sandbox/Dockerfile) has no Docker, so a Railway or Hetzner box with such crates fails to build from the site. For now the README says to deploy that one from the desktop.

Options

• Put a Rust toolchain in the deploy image, so the crates build natively on linux/amd64. The container already is linux/amd64, so this works for x86 boxes (cpx*, Railway). It makes the image bigger and the build slower, inside the 13-minute budget.
• Build the crates in CI and commit or upload native/dist, so the hosted build has nothing to compile.
• Refuse clearly up front: when the config read sees native crates on a box target, the panel says "deploy this one from the desktop" before the run starts.

🤖 Generated with Claude Code