The ci-cpp image was likely built for linux/amd64; the eulernest runner
is linux/arm64 (Raspberry Pi), so the container exited immediately
without running any steps (task 102 log: 10 lines, no step output).
Fix: run directly on the host runner and install cmake/g++ via apt-get
(same approach as the previously working workflow).
Also pin --platform=linux/arm64 in Dockerfile.ci-cpp so the next
image build produces the correct architecture. Once the image is pushed,
re-add the container: block to the workflow.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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