The HTTP/2 multiplexing libcurl uses by default makes clones from some servers fail mid-transfer with "RPC failed; curl 92 HTTP/2 stream not closed cleanly". Every source dependency in the image, and the project's own FetchContent step, clones over HTTPS, so pin HTTP/1.1 system-wide. Orthogonal to GitHub's unauthenticated-download throttling, which answers git-upload-pack with 401 regardless of the HTTP version. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01B6iekpDa2xiKobEj1R5xnp