[wdconinc]

Summary

• eic-shell workflow: passes -DCMAKE_CXX_STANDARD=20 explicitly instead of relying on the CMake default. It is set as a workflow-level env, not a matrix dimension, so the job names required by the main ruleset (build (clang++, Debug), build (clang++, Release), build (g++, Release)) stay the same.
• Legacy GitLab CI: the juggler:local build and the clang-tidy run move from C++17 to C++20. The headers already require C++20 (std::integral/std::floating_point in random.h, requires clauses in property.h), so the C++17 job could not build main.

Test plan

• CI

🤖 Generated with Claude Code

[Copilot]

🟢 Approval recommended

The review surfaced no outstanding issues, as the CI changes explicitly set C++20 to match headers that already require C++20 concepts, with no conflicting C++17 references elsewhere.

No open issues 🎉

What changed in this PR

This PR makes the CI pipelines build with C++20 explicitly rather than relying on CMake's default. This aligns the build configuration with the code, whose headers already require C++20 features (concepts like std::integral/std::floating_point and requires clauses). Setting the standard in CI guards against environments or future changes where the default might differ.

Changes:

• GitLab CI: bump the juggler:local matrix CMAKE_CXX_STANDARD from 17 to 20 and the clang-tidy -extra-arg from -std=c++17 to -std=c++20.
• GitHub Actions (linux-eic-shell): add a workflow-level CMAKE_CXX_STANDARD: 20 env and pass -DCMAKE_CXX_STANDARD to the CMake configure step.
• Keeps the standard as a workflow-level env (not a matrix dimension) so required job names stay unchanged.

File	Description
.gitlab-ci.yml	Moves the local build matrix and clang-tidy analysis from C++17 to C++20 so they can compile main.
.github/​workflows/​linux-eic-shell.yml	Adds a C++20 env var and passes it explicitly to the CMake configure step without altering matrix-derived job names.

_{Review effort: Balanced}