diff --git a/.github/actions/build_pypi_dist/action.yml b/.github/actions/build_pypi_dist/action.yml
new file mode 100644
index 0000000..5c5af8e
--- /dev/null
+++ b/.github/actions/build_pypi_dist/action.yml
@@ -0,0 +1,361 @@
+# Copyright 2026 NWChemEx-Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+name: Build PyPI Distribution
+description: >-
+  Checkout and build a repository's sdist and/or wheel into dist/, verifying
+  the metadata and that the wheel installs cleanly. Does NOT publish --
+  the calling job must add its own pypa/gh-action-pypi-publish step
+  afterwards, as a sibling step never nested inside another composite
+  action: gh-action-pypi-publish's own docker-trampoline image-tag
+  resolution breaks when called from within a composite action (a known
+  upstream limitation, actions/runner#2473). Runs on a bare runner
+  (no `container:`).
+
+inputs:
+  cibw_build:
+    description: >-
+      A cibuildwheel CIBW_BUILD selector (e.g. cp312-manylinux_x86_64). When
+      set, the wheel is built with pypa/cibuildwheel instead of `python -m
+      build`, for a compiled package that needs a manylinux/macOS-portable
+      wheel. Leave unset for a pure-Python package with no compiled extension
+      (e.g. NWXCMake itself) -- a package with a CMakeLists.txt should always
+      set this, since a wheel built directly (not via cibuildwheel) isn't
+      manylinux-portable and PyPI will reject it.
+      Intended to be called once per {os, cibw_build} matrix leg from the
+      calling workflow; the job must NOT run inside a `container:`, since
+      cibuildwheel manages its own (nested) build containers on Linux.
+    required: false
+    default: ""
+  build_sdist:
+    description: >-
+      Whether this invocation ALSO builds the source distribution, in
+      addition to the wheel. Does not affect the wheel itself -- that is
+      always built whenever cibw_build is set, regardless of this input.
+      Only relevant to multi-platform matrices: every leg would build
+      byte-identical sdist content, and PyPI rejects re-uploading an
+      existing filename, so set this to "true" on exactly one leg and
+      "false" on the rest to publish the sdist once instead of once-per-leg.
+      Ignored (always true) on the plain, non-cibw_build path, since
+      there's only ever one leg there.
+    required: false
+    default: "true"
+  extra_index_url:
+    description: >-
+      Extra package index passed to the post-build `pip install` sanity
+      check (e.g. https://test.pypi.org/simple/), in addition to the
+      default index. Needed when this package's runtime dependencies are
+      other nwx packages that only exist on that extra index (e.g. a
+      TestPyPI-only publish chain) -- without it, the verification install
+      can only ever resolve dependencies that are already on the default
+      index. Leave unset for a package with no such dependencies.
+    required: false
+    default: ""
+  needs_mpi:
+    description: >-
+      Whether the cibuildwheel build needs an MPI installation. The
+      manylinux/macOS cibuildwheel containers are minimal and don't have
+      one, unlike the ambient dev matrix (see setup_nwx_dev_env). When
+      "true", installs openmpi3-devel (via EPEL) inside the manylinux
+      container and puts its bin/ on PATH so CMake's find_package(MPI)
+      succeeds there, and installs open-mpi via Homebrew on macOS. Ignored
+      when cibw_build is unset (the plain, non-cibuildwheel path assumes
+      the ambient runner already has whatever the package needs).
+    required: false
+    default: "false"
+  needs_boost:
+    description: >-
+      Whether the cibuildwheel build needs Boost. The manylinux/macOS
+      cibuildwheel containers are minimal and don't have it. When "true",
+      installs boost-devel (via EPEL) inside the manylinux container and
+      boost via Homebrew on macOS. Ignored when cibw_build is unset.
+    required: false
+    default: "false"
+  needs_blas:
+    description: >-
+      Whether the cibuildwheel build needs a BLAS/LAPACK installation (e.g.
+      transitively via GauXC). The manylinux/macOS cibuildwheel containers
+      are minimal and don't have one. When "true", installs openblas-devel
+      and lapack-devel (via EPEL) inside the manylinux container, and
+      openblas via Homebrew on macOS (pointing CMAKE_PREFIX_PATH at it,
+      since it's keg-only there). Ignored when cibw_build is unset.
+    required: false
+    default: "false"
+  needs_eigen:
+    description: >-
+      Whether the cibuildwheel build needs an installed Eigen3 CMake config
+      (e.g. libint2's own CMakeLists does its own find_package(Eigen3),
+      independent of and unsatisfied by nwxcmake's own FetchContent'd Eigen
+      target). The manylinux/macOS cibuildwheel containers don't have one.
+      When "true", installs eigen3-devel (via EPEL) inside the manylinux
+      container and eigen via Homebrew on macOS. Ignored when cibw_build is
+      unset.
+    required: false
+    default: "false"
+  needs_openmp:
+    description: >-
+      Whether the cibuildwheel build needs OpenMP (e.g. transitively via
+      GauXC, which unconditionally find_package(OpenMP)s). Linux's gcc
+      ships its own OpenMP runtime (libgomp) so no extra provisioning is
+      needed there; AppleClang has no built-in OpenMP support, so on macOS
+      this installs libomp via Homebrew and points scikit-build-core's
+      SKBUILD_CMAKE_ARGS at it (CMake's FindOpenMP can't locate Homebrew's
+      keg-only libomp on its own). Ignored when cibw_build is unset.
+    required: false
+    default: "false"
+
+runs:
+  using: composite
+  steps:
+    - name: Checkout Source
+      uses: actions/checkout@v4
+      with:
+        fetch-depth: 0
+        fetch-tags: true
+
+    - name: Set up Python
+      uses: actions/setup-python@v5
+      with:
+        python-version: "3.x"
+
+    - name: Install Packaging Tools
+      shell: bash
+      run: pip install --quiet build twine
+
+    # Uses the normal (isolated) build-system.requires resolution, i.e. the
+    # same git-fetched nwxcmake a real `pip install` from PyPI would use, so
+    # this publishes exactly what a fresh `pip install` would build.
+    - name: Build Source Distribution
+      if: inputs.build_sdist == 'true'
+      shell: bash
+      run: python -m build --sdist --outdir dist
+
+    # Building the wheel from the *extracted sdist* (rather than the repo
+    # checkout) catches packaging bugs where a file the build needs was
+    # never included in the sdist manifest -- publishing that wheel
+    # unbuilt-from-sdist could otherwise ship silently broken. Only applies
+    # to the plain path: cibuildwheel builds its own way (see below) and
+    # doesn't need this repo's build-system.requires forwarded a second time.
+    - name: Build Wheel From Source Distribution
+      if: inputs.cibw_build == ''
+      shell: bash
+      run: |
+        sdist=$(ls dist/*.tar.gz)
+        rm -rf sdist_extracted
+        mkdir sdist_extracted
+        tar -xzf "${sdist}" -C sdist_extracted --strip-components=1
+
+        python -m build --wheel --outdir dist sdist_extracted
+
+    # Composes the CIBW_BEFORE_ALL_*/CIBW_ENVIRONMENT_* values in a shell
+    # step (rather than inline ternary expressions in the cibuildwheel env:
+    # block below) so needs_mpi and needs_boost can each independently
+    # contribute a clause without one clobbering the other.
+    - name: Compute cibuildwheel System Dependencies
+      if: inputs.cibw_build != ''
+      shell: bash
+      run: |
+        before_linux=()
+        before_macos=()
+        env_linux=()
+        env_macos=("MACOSX_DEPLOYMENT_TARGET=11.0")
+
+        if [ "${{ inputs.needs_mpi }}" = "true" ]; then
+          # Built from source at the *exact* version Ubuntu 24.04's apt
+          # package provides (see setup_nwx_dev_env), not EPEL's openmpi3
+          # (3.1.3) as before -- OpenMPI's ABI is not guaranteed compatible
+          # across major versions. EPEL7 (manylinux2014's package repo) has
+          # no openmpi4 package at all, so this can't be a yum install. Still
+          # needed even though the wheel no longer vendors MPI (see
+          # CIBW_REPAIR_WHEEL_COMMAND_LINUX below): the extension must be
+          # *compiled* against a matching OpenMPI to link correctly against
+          # whatever system OpenMPI the wheel resolves to at runtime.
+          #
+          # --disable-dlopen got MPI_Init's MCA shmem component selection
+          # working (previously failed: "opal_shmem_base_select failed",
+          # since auditwheel only bundles a wheel's DT_NEEDED dependencies
+          # found via ldd, not the dlopen()'d MCA plugin .so files normally
+          # living under $prefix/lib/openmpi/), but a vendored wheel install
+          # still crashes one step later: OpenMPI's singleton-mode ORTE
+          # startup (ess_singleton_module.c) needs to locate the `orted`
+          # daemon executable itself, and auditwheel/delocate only ever
+          # bundle shared libraries, never the accompanying bin/ executables
+          # -- "A system-required executable could not be found". Vendoring
+          # MPI into the wheel is a dead end; see CIBW_REPAIR_WHEEL_COMMAND
+          # below for the fix (exclude MPI libs, require system MPI instead).
+          before_linux+=(
+            "curl -fsSL https://download.open-mpi.org/release/open-mpi/v4.1/openmpi-4.1.6.tar.gz -o /tmp/openmpi.tar.gz"
+            "mkdir -p /tmp/openmpi-src"
+            "tar -xzf /tmp/openmpi.tar.gz -C /tmp/openmpi-src --strip-components=1"
+            "cd /tmp/openmpi-src && ./configure --prefix=/usr/local/openmpi --disable-mpi-fortran --disable-dlopen"
+            "cd /tmp/openmpi-src && make -j\$(nproc) install"
+          )
+          env_linux+=("PATH=/usr/local/openmpi/bin:\$PATH" "LD_LIBRARY_PATH=/usr/local/openmpi/lib:\$LD_LIBRARY_PATH")
+          # auditwheel repair normally bundles every DT_NEEDED lib (incl.
+          # libmpi/libopen-rte/libopen-pal) into the wheel via
+          # RPATH-relocation. Excluding them here means the wheel links
+          # against whatever libmpi.so.40 is on the *runtime* system's
+          # linker path instead -- the one that ships with a real OpenMPI
+          # install (incl. its bin/orted), which setup_nwx_dev_env already
+          # provides ambient (libopenmpi-dev/openmpi-bin) and which end users
+          # need to install themselves (documented as a runtime requirement).
+          #
+          # Exact sonames (libmpi.so.40), NOT a glob (libmpi*): cibuildwheel
+          # v2.22.0's manylinux2014 image (quay.io/pypa/manylinux2014_x86_64:
+          # 2024.11.16-1) bakes in auditwheel 6.1.0, whose --exclude does a
+          # plain `soname in exclude` set-membership check (confirmed by
+          # reading that exact container's lddtree.py) -- fnmatch/glob
+          # support for --exclude was only added in a later auditwheel
+          # release. A glob pattern silently matches nothing and bundles the
+          # library anyway (reproduced locally via Docker: 'libmpi*' bundled
+          # libmpi/libopen-rte/libopen-pal same as no --exclude at all;
+          # 'libmpi.so.40' correctly excluded it, and since libopen-rte/
+          # libopen-pal are only reachable *through* libmpi in this tree,
+          # excluding libmpi.so.40 alone is sufficient -- auditwheel doesn't
+          # recurse into an excluded library's own dependencies).
+          {
+            echo "CIBW_REPAIR_WHEEL_COMMAND_LINUX=auditwheel repair --exclude 'libmpi.so.40' --exclude 'libopen-rte.so.40' --exclude 'libopen-pal.so.40' -w {dest_dir} {wheel}"
+          } >> "$GITHUB_ENV"
+          before_macos+=("brew install open-mpi")
+          # Homebrew's open-mpi (and its own deps: libpmix, libhwloc,
+          # libevent) are built against the actual runner OS, so their
+          # dylibs report a minimum target matching it (14.0 on macos-14) --
+          # higher than cibuildwheel's default arm64 target (11.0). delocate
+          # then refuses to tag the repaired wheel as 11.0-compatible, since
+          # that would be false. Raise the declared target to match what's
+          # actually bundled.
+          env_macos=("MACOSX_DEPLOYMENT_TARGET=14.0")
+        fi
+
+        if [ "${{ inputs.needs_boost }}" = "true" ]; then
+          # manylinux2014's plain boost-devel is 1.53.0, too old for headers
+          # some repos need (e.g. boost/container_hash/hash.hpp). EPEL's
+          # boost169-devel (parallel-installable, doesn't replace the base
+          # boost-devel) is the newest available via yum there, but installs
+          # under a versioned, non-default include path, so CMake's FindBoost
+          # needs to be pointed at it explicitly via BOOST_INCLUDEDIR.
+          before_linux+=("yum install -y boost169-devel")
+          env_linux+=("BOOST_INCLUDEDIR=/usr/include/boost169")
+          before_macos+=("brew install boost")
+        fi
+
+        if [ "${{ inputs.needs_blas }}" = "true" ]; then
+          before_linux+=("yum install -y epel-release" "yum install -y openblas-devel lapack-devel")
+          before_macos+=("brew install openblas")
+          # Quoted: cibuildwheel's CIBW_ENVIRONMENT parses space-separated
+          # KEY=VALUE tokens, and the $(brew --prefix ...) substitution's
+          # arguments contain a space, which would otherwise split it into
+          # two bogus tokens.
+          env_macos+=('CMAKE_PREFIX_PATH="$(brew --prefix openblas)"')
+        fi
+
+        if [ "${{ inputs.needs_eigen }}" = "true" ]; then
+          before_linux+=("yum install -y epel-release" "yum install -y eigen3-devel")
+          before_macos+=("brew install eigen")
+        fi
+
+        if [ "${{ inputs.needs_openmp }}" = "true" ]; then
+          before_macos+=("brew install libomp")
+          # AppleClang has no built-in OpenMP; CMake's FindOpenMP can't
+          # locate Homebrew's keg-only libomp without explicit hints. Quoted
+          # as a single token for the same reason as CMAKE_PREFIX_PATH above.
+          env_macos+=('SKBUILD_CMAKE_ARGS="-DOpenMP_C_FLAGS=-Xpreprocessor -fopenmp -I$(brew --prefix libomp)/include;-DOpenMP_C_LIB_NAMES=omp;-DOpenMP_CXX_FLAGS=-Xpreprocessor -fopenmp -I$(brew --prefix libomp)/include;-DOpenMP_CXX_LIB_NAMES=omp;-DOpenMP_omp_LIBRARY=$(brew --prefix libomp)/lib/libomp.dylib"')
+        fi
+
+        join_and() {
+          local out="" item
+          for item in "$@"; do
+            if [ -z "$out" ]; then out="$item"; else out="$out && $item"; fi
+          done
+          echo "$out"
+        }
+
+        {
+          echo "CIBW_BEFORE_ALL_LINUX=$(join_and "${before_linux[@]}")"
+          echo "CIBW_BEFORE_ALL_MACOS=$(join_and "${before_macos[@]}")"
+          echo "CIBW_ENVIRONMENT_LINUX=${env_linux[*]}"
+          echo "CIBW_ENVIRONMENT_MACOS=${env_macos[*]}"
+        } >> "$GITHUB_ENV"
+
+    # cibuildwheel manages its own (manylinux/macOS) build images, so it
+    # builds straight from the repo checkout rather than an extracted sdist.
+    - name: Build Wheel With cibuildwheel
+      if: inputs.cibw_build != ''
+      uses: pypa/cibuildwheel@v2.22.0
+      env:
+        CIBW_BUILD: ${{ inputs.cibw_build }}
+        CIBW_BUILD_VERBOSITY: "1"
+
+    - name: Collect cibuildwheel Output
+      if: inputs.cibw_build != ''
+      shell: bash
+      run: |
+        mkdir -p dist
+        mv wheelhouse/*.whl dist/
+
+    - name: Check Packaging Metadata
+      shell: bash
+      run: twine check dist/*
+
+    # A cibuildwheel wheel is tagged for one specific CPython (e.g. cp312),
+    # which usually differs from the ambient "Set up Python" 3.x (latest).
+    # Installing it there would fail with "not a supported wheel on this
+    # platform", so re-point PATH at a matching interpreter first.
+    - name: Determine cibuildwheel Python Version
+      if: inputs.cibw_build != ''
+      id: cibw_python_version
+      shell: bash
+      run: |
+        # e.g. "cp312-manylinux_x86_64" -> "3.12"
+        if [[ "${{ inputs.cibw_build }}" =~ ^cp([0-9])([0-9]+) ]]; then
+          echo "version=${BASH_REMATCH[1]}.${BASH_REMATCH[2]}" >> "$GITHUB_OUTPUT"
+        else
+          echo "::error::Could not parse a Python version out of cibw_build='${{ inputs.cibw_build }}'"
+          exit 1
+        fi
+
+    - name: Set up Python Matching cibuildwheel Target
+      if: inputs.cibw_build != ''
+      uses: actions/setup-python@v5
+      with:
+        python-version: ${{ steps.cibw_python_version.outputs.version }}
+
+    # The plain (non-cibw) path's wheel itself is version-agnostic
+    # (py3-none-any), but a pure-Python package's runtime dependencies can
+    # include other nwx-ecosystem packages that are compiled and only
+    # published for one CPython version (cp312, per platform_matrix.yaml's
+    # release_matrix) -- installing under whatever "Set up Python"'s "3.x"
+    # resolves to today (e.g. 3.14) would find no matching wheel for those
+    # and fall back to building them from source, which fails on this bare
+    # verification venv (no MPI/Boost/etc.). Re-point at 3.12 to match.
+    - name: Set up Python Matching Ecosystem Release Target
+      if: inputs.cibw_build == ''
+      uses: actions/setup-python@v5
+      with:
+        python-version: "3.12"
+
+    # Cheap safety net before publishing to a registry where a bad upload
+    # can only be yanked, never truly deleted: catch an unimportable wheel
+    # here rather than after it's live on PyPI.
+    - name: Verify Wheel Installs
+      shell: bash
+      run: |
+        python -m venv /tmp/build_pypi_dist_venv
+        . /tmp/build_pypi_dist_venv/bin/activate
+        wheel=$(ls dist/*.whl)
+        extra_index_args=()
+        if [ -n "${{ inputs.extra_index_url }}" ]; then
+          extra_index_args=(--extra-index-url "${{ inputs.extra_index_url }}")
+        fi
+        pip install --quiet "${extra_index_args[@]}" "${wheel}"
diff --git a/.github/actions/cmake_build/action.yml b/.github/actions/cmake_build/action.yml
new file mode 100644
index 0000000..fff89bf
--- /dev/null
+++ b/.github/actions/cmake_build/action.yml
@@ -0,0 +1,139 @@
+# Copyright 2025 NWChemEx-Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+name: CMake Build
+description: >-
+  Configure, build, and optionally test a repository with CMake using a
+  native (apt/Homebrew) compiler toolchain on Linux or macOS. The calling
+  job must provide python/pip on PATH (e.g. via actions/setup-python) for
+  the Python test step.
+
+inputs:
+  compiler:
+    description: "One of: gcc-14, clang-18. Installed via the native package manager (apt on Linux, Homebrew on macOS)."
+    required: true
+  run_cmake_tests:
+    description: "Whether to build and run the CTest (C++) test suite (sets -DBUILD_TESTING)."
+    required: false
+    default: "true"
+  run_python_tests:
+    description: "Whether to run the pytest (Python) test suite against the built pybind11 module."
+    required: false
+    default: "true"
+  cmake_opts:
+    description: "Additional CMake options to pass at configure time."
+    required: false
+    default: ""
+  extra_pip_packages:
+    description: "Extra packages to pip install into the ambient Python before the C++ test step (e.g. CTest-driven Python tests that import a pip-installed package)."
+    required: false
+    default: ""
+
+runs:
+  using: composite
+  steps:
+    - name: Setup NWX Dev Environment
+      uses: NWChemEx/.github/.github/actions/setup_nwx_dev_env@master
+      with:
+        compiler: ${{ inputs.compiler }}
+
+    # Some repos' CMake build invokes a Python codegen script at configure or
+    # build time (e.g. GauXC's gau2grid dependency imports numpy to generate
+    # C source), so this needs to run before Configure/Build below, not only
+    # before the Python test step later in this same file.
+    - name: Install Python Requirements
+      shell: bash
+      run: |
+        if [ -f requirements.txt ]; then
+          pip install --quiet -r requirements.txt
+        fi
+
+    - name: Cache Dependency Build Tree
+      uses: actions/cache@v4
+      with:
+        path: build/_deps
+        key: deps-${{ runner.os }}-${{ inputs.compiler }}-${{ github.run_id }}
+        restore-keys: |
+          deps-${{ runner.os }}-${{ inputs.compiler }}-
+
+    - name: Configure
+      shell: bash
+      run: |
+        build_testing=${{ inputs.run_cmake_tests == 'true' && 'ON' || 'OFF' }}
+
+        # Pin CMake's FindPython to the interpreter actions/setup-python put on
+        # PATH (and that "Install Python Requirements" above just installed
+        # into). Without this, CMake's own search can prefer a different
+        # ambient interpreter (e.g. a macOS Homebrew framework Python),
+        # leaving configure-time-installed packages invisible to build-time
+        # codegen scripts that embed a Python interpreter.
+        cmake -Bbuild -H. -GNinja \
+          -DCMAKE_INSTALL_PREFIX=./install \
+          -DCMAKE_C_COMPILER="${CC}" \
+          -DCMAKE_CXX_COMPILER="${CXX}" \
+          -DBUILD_TESTING="${build_testing}" \
+          -DPython_EXECUTABLE="$(command -v python3)" \
+          ${{ inputs.cmake_opts }}
+
+    - name: Build
+      shell: bash
+      run: cmake --build build --parallel
+
+    - name: Install Extra Pip Packages
+      if: inputs.extra_pip_packages != ''
+      shell: bash
+      # Runs before "Test C++" because CTest-driven Python tests use the
+      # ambient Python_EXECUTABLE, whose sys.path always includes
+      # site-packages regardless of CTest's PYTHONPATH override -- so any
+      # package such a test imports needs to be pip-installed here.
+      run: pip install --quiet ${{ inputs.extra_pip_packages }}
+
+    - name: Test C++
+      if: inputs.run_cmake_tests == 'true'
+      shell: bash
+      working-directory: build
+      # Some C++ tests embed a Python interpreter that imports this repo's
+      # own (and its dependencies') built pybind11 modules -- same PYTHONPATH
+      # need as the pytest step below, just computed relative to build/.
+      run: |
+        total_tests=$(ctest -N | grep "Total Tests:" | grep -oE "[0-9]+$")
+        if [ "${total_tests:-0}" -eq 0 ]; then
+            echo "::error::run_cmake_tests is true but zero CTest tests were found."
+            exit 1
+        fi
+        pythonpath=$(find . -name "*.so" -exec dirname {} \; | sort -u | paste -sd: -)
+        PYTHONPATH="$pythonpath" ctest -VV
+
+    - name: Test Python
+      if: inputs.run_python_tests == 'true'
+      shell: bash
+      run: |
+        pip install --quiet pytest
+
+        pythonpath=$(find build -name "*.so" -exec dirname {} \; | sort -u | paste -sd: -)
+        if [ -z "$pythonpath" ]; then
+            echo "::error::run_python_tests is true but no built Python module (*.so) was found under build/."
+            exit 1
+        fi
+
+        set +e
+        PYTHONPATH="$pythonpath" pytest -v
+        pytest_exit=$?
+        set -e
+
+        if [ "$pytest_exit" -eq 5 ]; then
+            echo "::error::run_python_tests is true but zero pytest tests were found."
+            exit 1
+        fi
+        exit "$pytest_exit"
diff --git a/.github/actions/pip_build/action.yml b/.github/actions/pip_build/action.yml
new file mode 100644
index 0000000..a10f927
--- /dev/null
+++ b/.github/actions/pip_build/action.yml
@@ -0,0 +1,98 @@
+# Copyright 2025 NWChemEx-Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+name: Pip Build
+description: >-
+  Build and optionally test a repository's Python package with pip, using a
+  native (apt/Homebrew) compiler toolchain on Linux or macOS. The calling
+  job must provide python/pip on PATH (e.g. via actions/setup-python).
+
+inputs:
+  compiler:
+    description: "One of: gcc-14, clang-18. Installed via the native package manager (apt on Linux, Homebrew on macOS)."
+    required: true
+  run_cmake_tests:
+    description: "Whether to build and run the CTest (C++) test suite (sets -DBUILD_TESTING)."
+    required: false
+    default: "true"
+  run_python_tests:
+    description: "Whether to install the package editable with its dev extras and run the pytest (Python) test suite."
+    required: false
+    default: "true"
+  pip_opts:
+    description: "Additional options to pass to pip install."
+    required: false
+    default: ""
+
+runs:
+  using: composite
+  steps:
+    - name: Setup NWX Dev Environment
+      uses: NWChemEx/.github/.github/actions/setup_nwx_dev_env@master
+      with:
+        compiler: ${{ inputs.compiler }}
+
+    - name: Cache Dependency Build Tree
+      uses: actions/cache@v4
+      with:
+        path: build/_deps
+        key: deps-${{ runner.os }}-${{ inputs.compiler }}-${{ github.run_id }}
+        restore-keys: |
+          deps-${{ runner.os }}-${{ inputs.compiler }}-
+
+    - name: Install
+      shell: bash
+      run: |
+        build_testing=${{ inputs.run_cmake_tests == 'true' && 'ON' || 'OFF' }}
+
+        if [ "${{ inputs.run_python_tests }}" == "true" ]; then
+            pip install -e ".[dev]" \
+              --config-settings=cmake.define.CMAKE_C_COMPILER="${CC}" \
+              --config-settings=cmake.define.CMAKE_CXX_COMPILER="${CXX}" \
+              --config-settings=cmake.define.BUILD_TESTING="${build_testing}" \
+              ${{ inputs.pip_opts }}
+        else
+            pip install . \
+              --config-settings=cmake.define.CMAKE_C_COMPILER="${CC}" \
+              --config-settings=cmake.define.CMAKE_CXX_COMPILER="${CXX}" \
+              --config-settings=cmake.define.BUILD_TESTING="${build_testing}" \
+              ${{ inputs.pip_opts }}
+        fi
+
+    - name: Test Python
+      if: inputs.run_python_tests == 'true'
+      shell: bash
+      run: |
+        set +e
+        pytest -v
+        pytest_exit=$?
+        set -e
+
+        if [ "$pytest_exit" -eq 5 ]; then
+            echo "::error::run_python_tests is true but zero pytest tests were found."
+            exit 1
+        fi
+        exit "$pytest_exit"
+
+    - name: Test C++
+      if: inputs.run_cmake_tests == 'true'
+      shell: bash
+      working-directory: build
+      run: |
+        total_tests=$(ctest -N | grep "Total Tests:" | grep -oE "[0-9]+$")
+        if [ "${total_tests:-0}" -eq 0 ]; then
+            echo "::error::run_cmake_tests is true but zero CTest tests were found."
+            exit 1
+        fi
+        ctest -VV
diff --git a/.github/actions/setup_nwx_dev_env/action.yml b/.github/actions/setup_nwx_dev_env/action.yml
new file mode 100644
index 0000000..31873f7
--- /dev/null
+++ b/.github/actions/setup_nwx_dev_env/action.yml
@@ -0,0 +1,120 @@
+# Copyright 2026 NWChemEx-Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+name: Setup NWX Dev Environment
+description: >-
+  Installs a C/C++ compiler plus CMake, Ninja, MPI, Boost, BLAS/LAPACK, and
+  Eigen3 via the native package manager (apt on Linux, Homebrew on macOS),
+  and exports CC/CXX to $GITHUB_ENV for later steps in the same job. Single
+  source of truth for this, shared by cmake_build and pip_build.
+
+inputs:
+  compiler:
+    description: "One of: gcc-14, clang-18."
+    required: true
+  needs_nwchem:
+    description: >-
+      Whether to install a real NWChem binary, for friend-integration tests
+      that shell out to the external NWChem quantum chemistry program (e.g.
+      FriendZone's nwx2molssi/nwx2ase NWChem wrappers, and NWChemEx's
+      compute_energy tests -- both gated behind
+      friendzone.friends.is_nwchem_enabled(), which checks whether `nwchem`
+      is on PATH). No apt or pip package ships the actual NWChem binary, only
+      Homebrew (macOS) and conda-forge (Linux, via a standalone micromamba
+      bootstrap -- no full Anaconda needed) do. Off by default: this is a
+      large, slow install that only a couple of repos' test suites need.
+    required: false
+    default: "false"
+
+runs:
+  using: composite
+  steps:
+    - name: Install Compiler and Dependencies
+      shell: bash
+      run: |
+        case "${{ runner.os }}_${{ inputs.compiler }}" in
+          Linux_gcc-14)
+            sudo apt-get update -y
+            sudo apt-get install -y gcc-14 g++-14 cmake ninja-build libopenmpi-dev openmpi-bin libboost-dev libopenblas-dev liblapack-dev libeigen3-dev
+            echo "CC=gcc-14"  >> "$GITHUB_ENV"
+            echo "CXX=g++-14" >> "$GITHUB_ENV"
+            ;;
+          Linux_clang-18)
+            sudo apt-get update -y
+            sudo apt-get install -y clang-18 libomp-18-dev cmake ninja-build libopenmpi-dev openmpi-bin libboost-dev libopenblas-dev liblapack-dev libeigen3-dev
+            echo "CC=clang-18"    >> "$GITHUB_ENV"
+            echo "CXX=clang++-18" >> "$GITHUB_ENV"
+            ;;
+          macOS_gcc-14)
+            brew install gcc@14 cmake ninja open-mpi boost openblas eigen
+            echo "CC=gcc-14"  >> "$GITHUB_ENV"
+            echo "CXX=g++-14" >> "$GITHUB_ENV"
+            echo "CMAKE_PREFIX_PATH=$(brew --prefix openblas)" >> "$GITHUB_ENV"
+            ;;
+          macOS_clang-18)
+            brew install llvm@18 libomp cmake ninja open-mpi boost openblas eigen
+            prefix=$(brew --prefix llvm@18)
+            libomp_prefix=$(brew --prefix libomp)
+            echo "CC=${prefix}/bin/clang"    >> "$GITHUB_ENV"
+            echo "CXX=${prefix}/bin/clang++" >> "$GITHUB_ENV"
+            echo "CMAKE_PREFIX_PATH=$(brew --prefix openblas);${libomp_prefix}" >> "$GITHUB_ENV"
+            # llvm@18's own clang has no bundled OpenMP runtime; find_package(OpenMP)
+            # needs omp.h/libomp.dylib on the compiler's default search paths to pass
+            # its "-fopenmp compiles" check and locate the library, and CPATH/LIBRARY_PATH
+            # are how Clang picks those up without needing explicit -I/-L flags threaded
+            # through every cmake_opts caller.
+            echo "CPATH=${libomp_prefix}/include" >> "$GITHUB_ENV"
+            echo "LIBRARY_PATH=${libomp_prefix}/lib" >> "$GITHUB_ENV"
+            ;;
+          *)
+            echo "::error::Unsupported (os, compiler): (${{ runner.os }}, ${{ inputs.compiler }})"
+            exit 1
+            ;;
+        esac
+
+    - name: Install NWChem
+      if: inputs.needs_nwchem == 'true'
+      shell: bash
+      run: |
+        case "${{ runner.os }}" in
+          Linux)
+            # No apt/pip package ships the real NWChem binary -- conda-forge
+            # is the only source of a precompiled one. Bootstrap a
+            # standalone micromamba (not a full Anaconda/conda install),
+            # install NWChem into its own env, then put just that env's
+            # bin/ on PATH via GITHUB_PATH rather than `conda activate`,
+            # so it doesn't shadow the Python venv the rest of the job uses.
+            "${SHELL}" <(curl -L micro.mamba.pm/install.sh)
+            "$HOME/.local/bin/micromamba" create -y -n nwchem -c conda-forge nwchem
+            echo "$HOME/micromamba/envs/nwchem/bin" >> "$GITHUB_PATH"
+            # conda-forge's nwchem is compiled with a hardcoded default
+            # NWCHEM_BASIS_LIBRARY pointing at the feedstock's own build
+            # directory (doesn't exist outside the build container), so
+            # basis set lookups fail unless overridden. The package's own
+            # etc/conda/activate.d/nwchem_env.sh sets these two vars
+            # correctly, but only on `conda activate`, which we don't do
+            # (just PATH, to avoid shadowing the job's Python venv) -- so
+            # set them explicitly instead. Confirmed via local repro
+            # (Docker) that a bare `nwchem` invocation missing these vars
+            # can hang indefinitely on some tasks (e.g. CCSD(T)) rather
+            # than fail cleanly, instead of the fast/clean "failed opening
+            # basis file" abort seen on simpler tasks (e.g. CCSD) --
+            # confirmed fixed by setting these.
+            echo "NWCHEM_BASIS_LIBRARY=$HOME/micromamba/envs/nwchem/share/nwchem/libraries/" >> "$GITHUB_ENV"
+            echo "NWCHEM_NWPW_LIBRARY=$HOME/micromamba/envs/nwchem/share/nwchem/libraryps/" >> "$GITHUB_ENV"
+            ;;
+          macOS)
+            brew install nwchem
+            ;;
+        esac
diff --git a/.github/workflows/deploy_nwx_docs.yaml b/.github/workflows/deploy_nwx_docs.yaml
index 8131844..e0df086 100644
--- a/.github/workflows/deploy_nwx_docs.yaml
+++ b/.github/workflows/deploy_nwx_docs.yaml
@@ -41,6 +41,22 @@ jobs:
             core.setFailed("doc_target must not be blank.")
       - name: Checkout Source
         uses: actions/checkout@v4
+      # Some repos' CMake build invokes a Python codegen script at configure
+      # or build time (e.g. GauXC's gau2grid dependency imports numpy to
+      # generate C source) using whichever python3 is on PATH by default in
+      # this container -- install into that same interpreter here, before
+      # CMake ever runs, rather than in the module-docs/Sphinx steps below
+      # (those activate /pyenv instead, a separate environment).
+      - name: Install Repo Python Build Dependencies
+        if: inputs.generate_module_docs == true
+        run: |
+          if [ -f requirements.txt ]; then
+            # This container's system python3 is PEP 668
+            # externally-managed; --break-system-packages is safe here
+            # since the whole container is ephemeral CI state anyway.
+            python3 -m pip install --quiet --break-system-packages -r requirements.txt
+          fi
+        shell: bash
       # These next two steps will configure CMake if required
       - name: Configure Only Docs
         if: |
diff --git a/.github/workflows/platform_matrix.yaml b/.github/workflows/platform_matrix.yaml
new file mode 100644
index 0000000..65d3147
--- /dev/null
+++ b/.github/workflows/platform_matrix.yaml
@@ -0,0 +1,56 @@
+# Copyright 2026 NWChemEx-Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+name: Platform Matrix
+# Central source of truth for the OS/compiler/cibw_build combinations
+# NWChemEx tests and publishes for. Emits two JSON matrix strings as outputs
+# for downstream jobs to consume via fromJSON().
+
+on:
+  workflow_call:
+    outputs:
+      release_matrix:
+        description: >-
+          JSON list of {os, cibw_build} objects for deploy_to_pypi
+          (compiled-package wheel matrix).
+        value: ${{ jobs.define_matrix.outputs.release_matrix }}
+      dev_matrix:
+        description: >-
+          JSON list of {os, compiler} objects for cmake_build/pip_build
+          (dev/test matrix).
+        value: ${{ jobs.define_matrix.outputs.dev_matrix }}
+
+jobs:
+  define_matrix:
+    runs-on: ubuntu-latest
+    outputs:
+      release_matrix: ${{ steps.set.outputs.release_matrix }}
+      dev_matrix: ${{ steps.set.outputs.dev_matrix }}
+    steps:
+      - id: set
+        shell: bash
+        run: |
+          release_matrix='[
+            {"os": "ubuntu-latest", "cibw_build": "cp312-manylinux_x86_64"},
+            {"os": "macos-14",      "cibw_build": "cp312-macosx_arm64"}
+          ]'
+          dev_matrix='[
+            {"os": "ubuntu-latest", "compiler": "gcc-14"},
+            {"os": "ubuntu-latest", "compiler": "clang-18"},
+            {"os": "macos-14",      "compiler": "gcc-14"},
+            {"os": "macos-14",      "compiler": "clang-18"}
+          ]'
+          echo "release_matrix=$(echo "$release_matrix" | jq -c .)" >> "$GITHUB_OUTPUT"
+          echo "dev_matrix=$(echo "$dev_matrix" | jq -c .)" >> "$GITHUB_OUTPUT"
diff --git a/.github/workflows/test_nwx_cmake_build.yaml b/.github/workflows/test_nwx_cmake_build.yaml
new file mode 100644
index 0000000..15b84b7
--- /dev/null
+++ b/.github/workflows/test_nwx_cmake_build.yaml
@@ -0,0 +1,76 @@
+# Copyright 2026 NWChemEx-Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+name: Test NWX CMake Build
+# Configure, build, and test a repository with CMake, across the shared
+# NWChemEx dev matrix (see platform_matrix.yaml).
+
+on:
+  workflow_call:
+    inputs:
+      run_cmake_tests:
+        description: "Whether to build and run the CTest (C++) test suite."
+        type: string
+        required: false
+        default: "true"
+      run_python_tests:
+        description: "Whether to run the pytest (Python) test suite against the built pybind11 module."
+        type: string
+        required: false
+        default: "true"
+      cmake_opts:
+        description: "Additional CMake options to pass at configure time."
+        type: string
+        required: false
+        default: ""
+      python_version:
+        description: "Python version to set up (passed to actions/setup-python)."
+        type: string
+        required: false
+        default: "3.x"
+      extra_pip_packages:
+        description: "Extra packages to pip install into the ambient Python before the C++ test step."
+        type: string
+        required: false
+        default: ""
+
+jobs:
+  platform_matrix:
+    uses: NWChemEx/.github/.github/workflows/platform_matrix.yaml@master
+
+  test_cmake_build:
+    needs: platform_matrix
+    strategy:
+      fail-fast: false
+      matrix:
+        include: ${{ fromJSON(needs.platform_matrix.outputs.dev_matrix) }}
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: Checkout Source
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ inputs.python_version }}
+      - name: CMake Build
+        uses: NWChemEx/.github/.github/actions/cmake_build@master
+        with:
+          compiler: ${{ matrix.compiler }}
+          run_cmake_tests: ${{ inputs.run_cmake_tests }}
+          run_python_tests: ${{ inputs.run_python_tests }}
+          cmake_opts: ${{ inputs.cmake_opts }}
+          extra_pip_packages: ${{ inputs.extra_pip_packages }}
diff --git a/.github/workflows/test_nwx_pip_build.yaml b/.github/workflows/test_nwx_pip_build.yaml
new file mode 100644
index 0000000..0307147
--- /dev/null
+++ b/.github/workflows/test_nwx_pip_build.yaml
@@ -0,0 +1,65 @@
+# Copyright 2026 NWChemEx-Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+name: Test NWX Pip Build
+# Build and test a repository's Python package with pip, across the shared
+# NWChemEx dev matrix (see platform_matrix.yaml).
+
+on:
+  workflow_call:
+    inputs:
+      run_cmake_tests:
+        description: "Whether to build and run the CTest (C++) test suite (sets -DBUILD_TESTING)."
+        type: string
+        required: false
+        default: "true"
+      run_python_tests:
+        description: "Whether to install the package editable with its dev extras and run the pytest (Python) test suite."
+        type: string
+        required: false
+        default: "true"
+      pip_opts:
+        description: "Additional options to pass to pip install."
+        type: string
+        required: false
+        default: ""
+
+jobs:
+  platform_matrix:
+    uses: NWChemEx/.github/.github/workflows/platform_matrix.yaml@master
+
+  test_pip_build:
+    needs: platform_matrix
+    strategy:
+      fail-fast: false
+      matrix:
+        include: ${{ fromJSON(needs.platform_matrix.outputs.dev_matrix) }}
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: Checkout Source
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.x"
+      - name: Pip Build
+        uses: NWChemEx/.github/.github/actions/pip_build@master
+        with:
+          compiler: ${{ matrix.compiler }}
+          run_cmake_tests: ${{ inputs.run_cmake_tests }}
+          run_python_tests: ${{ inputs.run_python_tests }}
+          pip_opts: ${{ inputs.pip_opts }}