Add the esbuild/swc pattern for distributing platform-specific native
binaries via npm optional dependencies. Each supported platform gets its
own @gsd/engine-{platform} package containing just the .node binary.
- 5 platform package stubs (darwin-arm64, darwin-x64, linux-x64-gnu,
linux-arm64-gnu, win32-x64-msvc) with os/cpu filters
- Rewritten native loader: tries npm package first, then local build
- Version sync script keeps platform packages in lock-step with root
- GitHub Actions workflow for cross-platform build + publish on tag push
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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