build: compile OpenPMIx from source for MPI plugin in Dockerfile

[sgopinath1]

Summary

Nightly and release builds with BUILD_MPI_PLUGIN=1 fail in the Docker builder because AlmaLinux 8 has no openpmix-devel package. The distro pmix-devel RPM (PowerTools) ships PMIx 2.2.x, which is below Spur's pmix_min_version (4.1.0).

This change builds OpenPMIx 5.0.3 from source in the AlmaLinux 8 builder stage when BUILD_MPI_PLUGIN=1, then compiles spur-mpi-pmix against the installed pkg-config metadata. Nightly/release tarballs can include a functional lib/spur/spur_mpi_pmix.so again.

Approach

• Add OPENPMIX_VERSION build arg (default 5.0.3).
• Enable PowerTools and install build deps (hwloc-devel, libevent-devel, python3, etc.).
• Configure/install OpenPMIx to /usr/local, run ldconfig, then cargo build -p spur-mpi-pmix with PKG_CONFIG_PATH set.
• cd /build before the cargo step so removing the OpenPMIx source tree does not leave the shell in a deleted directory.

No changes to spur-ci-infra — nightly/release build entirely inside this Dockerfile on GitHub-hosted runners.

Test plan

• Local nightly-equivalent build:

  DOCKER_BUILDKIT=1 docker build --target dist --output type=local,dest=./dist \
    --build-arg BUILD_MPI_PLUGIN=1 \
    --build-arg SPUR_GIT_SHA=$(git rev-parse --short=8 HEAD) \
    --build-arg SPUR_GIT_DIRTY=false .

• Verified dist/lib/spur/spur_mpi_pmix.so is produced
• Verified spur, spurctld, spurd, spur-k8s-operator in dist/bin/ (GLIBC_2.28)

[Copilot]

Pull request overview

This PR fixes Docker image builds (nightly/release dist target) when BUILD_MPI_PLUGIN=1 by building OpenPMIx from source on AlmaLinux 8, since the distro-provided PMIx packages are either unavailable (openpmix-devel) or too old (pmix-devel 2.x) for Spur’s minimum supported PMIx version.

Changes:

• Adds OPENPMIX_VERSION build arg and documents why OpenPMIx must be built from source on AlmaLinux 8.
• Enables PowerTools and installs build dependencies needed to compile and install OpenPMIx to /usr/local.
• Builds spur-mpi-pmix with PKG_CONFIG_PATH pointing at the installed OpenPMIx pkg-config metadata.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #602      +/-   ##
==========================================
+ Coverage   76.32%   76.48%   +0.16%     
==========================================
  Files         166      167       +1     
  Lines       65511    67824    +2313     
==========================================
+ Hits        49999    51871    +1872     
- Misses      15512    15953     +441     

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[biluriuday]

LGTM