fix: build the full image's C++ libraries like AtCoder and test the images with ojt in CI

[carbon-nil]

Summary

Make the full image's C++ libraries usable through ojt exactly as AtCoder links them, and test the images in CI.

• Abseil (9800ad7): install only 20250512.1.
  • apt's 20220623 sat in /usr/lib/<triplet>, which the linker searches before /usr/local/lib.
  • So programs got the old libraries with the new headers.
• ojt linking (d75969e):
  • ojt passed none of AtCoder's defines or libraries, so OR-Tools headers did not even compile, and Abseil / LightGBM / LibTorch did not link.
  • It now adds -fopenmp -DNOMINMAX -lstdc++exp like the judge.
  • In full, it also reads cxx/full-flags.txt: AtCoder's defines and -l list, with libraries the image lacks dropped at build time.
  • LightGBM is installed as a static library like AtCoder's.
  • LibTorch gets an rpath (and rpath-link for arm64's vendored libs).
• Abseil + OR-Tools from source (3c912b4, 1123a21, 815cd4e):
  • The prebuilt arm64 OR-Tools is an AlmaLinux build that re-exports libstdc++ symbols. Together with LibTorch it crashed before main (Abseil flag registration).
  • Both are now built from source with AtCoder's options (including GLPK) in a separate cxx-libs-build stage.
  • That stage is cached independently of the rest of full. It needs apt's Eigen, and its man pages are dropped so it can be copied into /usr/local.
  • GCC 15 moves into its own gcc stage so edits to light do not invalidate it.
• amd64 libtorch's protobuf (f6916df): delete the libprotobuf*.a bundled with libtorch, as AtCoder does. -L/opt/libtorch/lib made -lprotobuf pick that older copy.
• Tests in CI (450ed1b):
  • The build job loads the image it just built and runs test/light.sh (C++, Python, PyPy and Rust through ojt) or test/full.sh (the same, plus one program that uses Abseil, Boost, GMP, LightGBM, OR-Tools, LibTorch, Z3 and OpenMP together).
  • This replaces running ojt inside the Dockerfile. That tested an unfinished image, hit PyPI through oj's update check, and invalidated the cache below it.

Still different from AtCoder: 4 Boost libraries (charconv, contract, process, stacktrace_from_exception) are missing from Ubuntu's Boost 1.83 and are skipped. A follow-up PR moves to Boost 1.88.

Test

CI, all four builds including the new test step: https://github.com/carbon-nil/atcoder-docker/actions/runs/35998419705

• light (amd64 / arm64): ojt AC for C++, Python, PyPy, Rust
• full (amd64 / arm64): the same plus the combined library program

Earlier runs on this branch caught, in order:

• the arm64 OR-Tools + LibTorch crash
• the missing Eigen target
• the /usr/local/man symlink conflict
• the amd64 protobuf mix-up

🤖 Generated with Claude Code

https://claude.ai/code/session_01VQaZJRoT1k7VZ8ThsuLdFa