Split libcuopt wheel into separate routing/LP packages for PyPI publication

[ramakrishnap-nv]

Background

Publishing cuOpt to pypi.org (instead of only pypi.nvidia.com) would simplify installation, remove the need for --extra-index-url, and unblock security-conscious users who restrict installs to the main PyPI index.

The blocker is package size. The current libcuopt-cu12 wheel is ~542 MB compressed. PyPI enforces a 1 GB per-package limit and a soft 100 GiB per-project limit; headroom exists today but is not comfortable enough to commit to indefinitely, especially with features like multi-GPU PDLP added recently.

What this issue tracks

Split the single libcuopt wheel into separate wheels along solver boundaries:

• libcuopt-base-cu12 — libcuopt_base.so; dependency of every other package
• libcuopt-routing-cu12 — routing/VRP engine (libcuopt_routing.so)
• libcuopt-lp-cu12 — LP/MILP/QP solver (libcuopt_lp.so)
• libcuopt-grpc-cu12 — gRPC client (libcuopt_grpc.so); depends on both engines, see below
• libcuopt-cu12 — metapackage depending on all of the above, so existing installs are unaffected

libcuopt_base.so must be its own package rather than duplicated into the routing and LP wheels — two wheels owning the same installed path conflict.

The corresponding Python meta-packages (cuopt-vrp, cuopt-lp, etc.) would declare only the lib package they need, so users who only use routing don't pull in the LP solver and vice versa.

Component boundaries (measured on #1622, stripped)

Component	Size	External deps beyond rmm / rapids_logger
cuopt_base	1.3 MB	—
cuopt_routing	37 MB	cublas
cuopt_lp	59 MB	cublas, cusparse, nccl, cudss, TBB
cuopt_grpc	1.0 MB	grpc, protobuf, abseil

readelf -d confirms libcuopt_routing.so has no DT_NEEDED on libcuopt_lp.so and vice versa — the two engines are independent, so no C++ untangling is required.

libcuopt_grpc.so is the exception: it links both engines (proto mappers for LP and routing). As specified above, libcuopt-grpc-cu12 therefore pulls in everything. Either accept that, or split its LP and routing mappers into separate translation units so a routing-only gRPC client is possible. This is the only part of the split with real C++ work behind it.

Secondary benefit, distinct from the PyPI size limit: cusparse, nccl, and cudss are LP-only and ship as separate nvidia-* wheels — ~1.2 GB of uncompressed on-disk libraries in a local build environment. A routing-only install currently pulls all of them and never calls into them. This does not affect the per-package limit that motivates this issue, but it is a large win for end-user install footprint.

Prerequisites

PR #1622 (feat/split-routing-lp-libs) splits the monolithic libcuopt.so into component .so files (libcuopt_base, libcuopt_routing, libcuopt_lp, libcuopt_grpc). That clean boundary is required before this package split is possible without rearchitecting the C++ build. This issue should not be started until that PR merges.

Prior art

A POC splitting cuOpt into cuopt-common + per-solver packages was explored previously but deferred for other priorities. The .so boundary work in #1622 makes this cleaner than the prior attempt.

Work involved

• Relink the Cython extension modules against their actual components. All four of python/cuopt/cuopt/{routing,linear_programming/solver,grpc/linear_programming,distance_engine}/CMakeLists.txt currently set linked_libraries cuopt::cuopt. Until they point at cuopt::routing / cuopt::lp / cuopt::grpc, every extension pulls the full graph and the optional-dependency groups achieve nothing. Worth doing first as a standalone PR: it is small, it de-risks the packaging work, and a mislinked module fails to link rather than silently over-depending.
• Give each component its own install component; install(TARGETS ${CUOPT_COMPONENT_TARGETS} ... COMPONENT runtime) currently stages them together.
• Split header installation — install(DIRECTORY include/cuopt/) is monolithic today, so dev headers need to follow their component.
• New ci/build_wheel_libcuopt_{base,routing,lp,grpc}.sh scripts (modeled on existing ci/build_wheel_libcuopt.sh)
• New python/libcuopt_{base,routing,lp,grpc}/ package directories with pyproject.toml
• Per-package dependency sets in dependencies.yaml — this is where cudss/nccl/cusparse get attached to LP only
• Update python/cuopt/pyproject.toml optional-dependency groups to reference the split packages
• Update conda recipes accordingly
• Verify compressed sizes stay well under 750 MB per package (per RAPIDS guidance)
• Coordinate with RAPIDS build-infra on PyPI org registration (see rapidsai/build-infra#356)

Target

26.10 (too late for 26.08)