Cached CI apt downloads and dropped the unused apt CMake package (#823)dev

On 23 Oct 2026 the Ubuntu mirror served package files at 50 to 250 KB/s while still
serving indexes at 12 MB/s. The ThreadX and RISC-V install steps timed out on all three
attempts, inside the 11 MB cmake package and the 58 MB qemu-system-misc package. Every
run downloads the same packages again, and the cmake one was never used: install.sh
installs CMake with pip, and the runner image's own CMake comes first on PATH.

regression_template.yml now restores the .deb files from the Actions cache before the
install step, points apt's archive directory at them through an apt.conf.d entry, and
saves them straight after the install. Every caller's install script gets this
unchanged, and the new apt_cache input turns it off. The key is the runner image and a
hash of the install script, falling back to the closest older cache. apt checks each
cached .deb against the signed index, so a cache cannot change what is installed.
install.sh no longer installs CMake from apt, and install_riscv.sh does so only when no
CMake is on PATH.

Run twice on a fork: the first run saved 19 MB for install.sh and 58 MB for
install_riscv.sh; the second restored both and fetched 0 B of 20.4 MB and 0 B of
61.3 MB of archives. In both runs the cache, install and build steps passed on all four
jobs, which then stopped at Configure GitHub Pages, not enabled on the fork.

Assisted-by: Claude Code (Opus 5.5) <[email protected]>

0 files changed, 0 insertions, 0 deletions