scripts/cpp-ref-key.sh names a harness/cpp/build.sh output (upstream commit plus a
hash of CMakeLists.txt, build.sh, stubs/**, patches/**). The new cpp-reference
workflow builds it on Ubuntu 24.04 and publishes it as GitHub Release
cpp-ref-<key>; scripts/fetch-cpp.sh downloads and verifies it (curl, no token) or
falls back to build.sh. CI's difftest job fetches instead of building and runs
Rust and the cc-compiled shims through sccache.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Pfe7dodPG5rpuN9B8QcnuX
bherbruck