Add R language SDK

[clemensv]

Summary

Adds an official R language SDK (r/) alongside the existing SDKs. It mirrors the Ruby SDK's architecture: because interpreted recursive validation is slow, the R package reuses the proven C validation engine through a thin compiled .Call shim rather than reimplementing the validator in R.

The shim dlopens a prebuilt json_structure shared library downloaded from GitHub Releases on first use (or pointed at by JSONSTRUCTURE_LIB_PATH). Nothing is vendored, and the package is intentionally not on CRAN (CRAN forbids downloading binaries at runtime).

What's included

• r/src/shim.c, r/src/init.c — dynamic loading (dlopen/dlsym on Unix, LoadLibraryExW on Windows), the C ABI re-declared to match c/include/json_structure/*.h exactly, and columnar .Call result marshaling. Registers 5 routines with R_useDynamicSymbols(FALSE) / R_forceSymbols(TRUE).
• r/R/ — idiomatic public API: js_validate_schema[_strict](), js_validate_instance[_strict](), is_valid(), js_error_messages() / js_warning_messages(), as.data.frame(), plus lazy library loading, the binary downloader/cache, and a faithful port of Ruby's R-side extension-keyword checks (units, relations, $uses gating, identifiers, tuple $ref, enum typing) — defensively tryCatch-wrapped so it can never turn a passing base result into a failure.
• r/tests/testthat/ — pure-R tests (run without the binary), binding tests, and shared-corpus conformance tests (mirroring Ruby's test_assets_spec.rb) that skip gracefully when the native library or test-assets/ are unavailable.
• r/man/ — documentation for every exported function.
• .github/workflows/r.yml — new CI: R CMD check + conformance across ubuntu/macos (R release + oldrel-1), a Windows shim-compile job, a lint job, and a release-on-tag job that uploads the R source tarball.

Shared prerequisite: C release assets

js_validate_* downloads the prebuilt library from
releases/download/vX.Y.Z/json_structure-<os>-<arch>.tar.gz. The C release job previously published only versioned workflow artifacts, so this URL would 404 for both Ruby and R. This PR makes an additive fix to .github/workflows/c.yml to also attach installer-named archives (json_structure-linux-x86_64, json_structure-macos-arm64, json_structure-windows-x86_64) to the GitHub Release. No existing behavior is removed.

Validation note

There is no R runtime or C compiler in the authoring environment, so the package was validated by rigorous static review plus an independent code review:

• The re-declared C ABI (structs, severity enum, function signatures) was checked field-by-field against the real headers — exact match; validator structs are minimal { options }, so the stack allocations cannot overflow.
• Every NAMESPACE export and S3 method has a matching definition and man/ alias.
• Reviewer-flagged issues were fixed: Windows non-ASCII paths now use LoadLibraryExW; -ldl is linked only on Linux/Solaris (via a GNU-make conditional, declared in SystemRequirements) so macOS builds cleanly; and the augmentation keyword sets were aligned exactly to the Ruby constants.

End-to-end compile/run is exercised by the new CI.

Website

Documentation for the project website is in the companion PR in json-structure/site.

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Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com

[clemensv]

Companion website documentation PR: json-structure/site#5

[clemensv]

Note: the Build and Test (windows-latest) check (from the pre-existing c.yml workflow) is failing due to environmental CI drift unrelated to this PR — the GitHub-hosted Windows image now ships CMake 4.3 / VS 2026, which rejects the repo's -DCMAKE_POLICY_VERSION_MINIMUM=3.5 handling (Invalid CMAKE_POLICY_VERSION_MINIMUM value \\3\\). This job is not modified by this PR (the only c.yml change here is additive, to the tag-only release job) and it also fails on a fresh master build. The R SDK builds the C library only on Ubuntu/macOS (both green) and compiles just the shim on Windows via Rtools, so it does not exercise the broken path. Fixing the C/Windows CMake incompatibility is out of scope for this SDK addition.

[clemensv]

C workflow windows-latest failure — fixed ✅

Root cause (environmental, surfaced by the new windows-2025-vs2026 runner image shipping CMake 4.3):

The Configure CMake steps run under PowerShell on Windows, which splits unquoted native-command arguments at the decimal point. So:

• -DCMAKE_POLICY_VERSION_MINIMUM=3.5 → reached CMake as 3 (with .5 as a separate argument)
• -DJSON_STRUCTURE_VERSION=0.1.0 → reached CMake as 0

CMake 4.3 then rejected configure with Invalid CMAKE_POLICY_VERSION_MINIMUM value "3". Bash on Linux/macOS never splits these, which is why only windows-latest failed. (The version arg being silently truncated to 0 was a latent bug too.)

Fix (99dfc14): quote the -D arguments in all three Configure CMake steps so PowerShell passes them intact. Verified locally that PowerShell now forwards 3.5/0.1.0 unsplit and that CMake configures cleanly.

Result: the C SDK workflow is now fully green on this branch — Build and Test on ubuntu/macos/windows + Valgrind all pass.

[clemensv]

Reorg: this PR no longer touches c.yml. The Windows CMake configure fix and the release-asset attachment now live in #178, so this is a pure R-package PR. It no longer triggers the C SDK workflow; the R SDK workflow covers it end-to-end.