Identify C++ CI matrix jobs with a generated runId

[nikobockerman]

The preset-name step built a string per matrix job by reassembling the four axes in shell. Its name no longer described it: the CMake preset is the literal ci, and the string's only consumers are the Conan cache key prefixes in cmake-project-setup and cmake-project-finalize. Now that the generator emits the matrix, the same value can come from the entry it already describes, so the step is redundant.

Add a runId field, joining every field of the entry so it stays unique by construction even if the matrix grows another axis, and read it as conan-${{ matrix.runId }} where the cache prefix is needed. The prefixes must stay distinct per scenario: cmake-project-setup falls back to restoring on the bare prefix, so a shared one would have every job pull a sibling configuration's packages, miss on package_id and rebuild from source anyway.

The vestigial ci- infix is dropped, since it described the preset name this string no longer is. That changes every prefix, so the existing Conan caches are orphaned and the first run rebuilds from source before saving under the new keys.

[Copilot]

Pull request overview

Updates the C++ CI workflow to use a generated, per-matrix-entry identifier (runId) for Conan cache key prefixes, removing the redundant shell step that previously reconstructed a preset-name-like string.

Changes:

• Remove the preset-name step from the workflow and switch Conan cache key prefixes to conan-${{ matrix.runId }}.
• Extend the CI matrix generator to emit a runId field derived from the matrix entry fields.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
.github/workflows/cpp-build-test-run.yaml	Drops the preset-name step and uses matrix.runId for Conan cache key prefixes in setup/finalize steps.
.github/scripts/generate-cpp-ci-config.py	Adds runId to generated matrix entries by joining the matrix entry fields.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

Suppressed comments (1)

.github/scripts/generate-cpp-ci-config.py:420

• Avoid using assert for validating runId uniqueness. Python assertions can be stripped with -O, which would silently skip this safety check and potentially cause cache-key collisions. Use an explicit runtime check and raise an exception instead.

    # Two jobs sharing a runId would quietly share one Conan cache bucket, each
    # restoring the other's packages and rebuilding anyway. Nothing downstream
    # would fail, so catch it here.
    run_ids = {entry["runId"] for entry in include}
    assert len(run_ids) == len(include), "runId values are not unique"