refactor(ci): ♻️ make the justfile the single source of build commands

.devcontainer/Dockerfile

@@ -2,9 +2,12 @@ FROM ghcr.io/astral-sh/uv:latest AS uv
 
 FROM mcr.microsoft.com/devcontainers/base:ubuntu26.04
 
-# install needed packages
+COPY tools/packages/apt.txt tools/packages/apt-mpi.txt /tmp/packages/
+
 RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
-    && apt-get -y install \
+    && sed -e 's/#.*//' -e 's/[[:space:]]*$//' /tmp/packages/*.txt \
+    | grep -v '^$' \
+    | xargs apt-get -y install \
     clang \
     clang-tidy \
     clang-format \
@@ -17,12 +20,7 @@ RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
     lcov \
     ninja-build \
     python3 \
-    openmpi-bin \
-    libboost-dev \
-    libboost-test-dev \
-    libhwloc-dev \
-    libmsgpack-cxx-dev \
-    libopenmpi-dev \
+    && rm -rf /tmp/packages \
     && apt-get autoremove -y \
     && apt-get clean -y \
     && rm -rf /var/lib/apt/lists/*

.github/actions/setup/action.yml

@@ -0,0 +1,77 @@
+name: Set up a monoprop CI environment
+description: >-
+  Install just, uv, and the packages listed in tools/packages/. Installs tools,
+  not commands: anything a developer also runs belongs in the justfile.
+
+inputs:
+  python-version:
+    description: Python version handed to setup-uv.
+    required: false
+    default: "3.11"
+  cache-suffix:
+    description: >-
+      setup-uv cache key suffix. Must differ per build configuration, or a
+      restored cache carries a wheel built for another one.
+    required: true
+  mpi:
+    description: Install an MPI implementation ("on" or "off").
+    required: false
+    default: "off"
+
+runs:
+  using: composite
+  steps:
+    - name: Install just
+      uses: extractions/setup-just@v4.0.0
+
+    - name: Install the latest version of uv
+      uses: astral-sh/setup-uv@v10.0.1
+      with:
+        enable-cache: true
+        cache-suffix: ${{ inputs.cache-suffix }}
+        python-version: ${{ inputs.python-version }}
+
+    - name: Install system dependencies
+      shell: bash
+      env:
+        MPI: ${{ inputs.mpi }}
+      run: |
+        set -euo pipefail
+
+        # macOS runners still ship bash 3.2, so no mapfile and no ${var,,}.
+        packages=()
+        add_list() {
+          while IFS= read -r package; do
+            packages+=("$package")
+          done < <(sed -e 's/#.*//' -e 's/[[:space:]]*$//' "$1" | grep -v '^$' || true)
+        }
+
+        if [[ "$RUNNER_OS" == "macOS" ]]; then
+          prefix=tools/packages/brew
+        else
+          prefix=tools/packages/apt
+        fi
+
+        add_list "$prefix.txt"
+        if [[ "$(printf '%s' "$MPI" | tr '[:upper:]' '[:lower:]')" =~ ^(on|true|yes|1)$ ]]; then
+          add_list "$prefix-mpi.txt"
+        fi
+
+        # Derive the package from CXX, so a matrix lane needs no list of its own.
+        if [[ -n "${CXX:-}" ]] && ! command -v "$CXX" > /dev/null; then
+          case "$CXX" in
+            clang++*) packages+=("clang${CXX#clang++}") ;;
+            g++*) packages+=("g++${CXX#g++}") ;;
+            *)
+              echo "CXX=$CXX is not installed and no package name can be derived from it" >&2
+              exit 2
+              ;;
+          esac
+        fi
+
+        if [[ "$RUNNER_OS" == "macOS" ]]; then
+          brew install "${packages[@]}"
+        else
+          sudo apt-get update
+          sudo apt-get install -y "${packages[@]}"
+        fi

.github/workflows/bench.yml

@@ -47,23 +47,15 @@ jobs:
         with:
           fetch-depth: 0
 
-      - name: Install dependencies
-        run: |
-          sudo apt-get update
-          sudo apt-get install -y just libopenmpi-dev openmpi-bin libboost-dev libhwloc-dev
-
-      - name: Install the latest version of uv
-        uses: astral-sh/setup-uv@v10.0.1
+      - name: Set up the build environment
+        uses: ./.github/actions/setup
         with:
-          enable-cache: true
           cache-suffix: benchmark
-          python-version: "3.11"
 
       - name: Install package
         env:
           SKBUILD_CMAKE_DEFINE: monoprop_ENABLE_CXX_UNIT_TESTS=OFF
-        run: |
-          uv sync --no-progress --group bench --all-extras -v
+        run: just build --group bench
 
       - name: Run benchmarks
         env:

.github/workflows/copilot-setup-steps.yml

@@ -26,18 +26,11 @@ jobs:
         with:
           fetch-depth: 0
 
-      - name: Install dependencies from APT
-        run: |
-          sudo apt-get update
-          sudo apt-get install -y just libopenmpi-dev openmpi-bin libboost-dev libboost-test-dev libmsgpack-cxx-dev libhwloc-dev
-
-      - name: Install the latest version of uv
-        uses: astral-sh/setup-uv@v10.0.1
+      - name: Set up the build environment
+        uses: ./.github/actions/setup
         with:
-          enable-cache: true
           cache-suffix: copilot
-          python-version: "3.11"
+          mpi: "on"
 
       - name: Install package
-        run: |
-          uv sync --all-groups --all-extras -v
+        run: just build --all-groups

.github/workflows/docpages.yml

@@ -43,17 +43,10 @@ jobs:
           # grab the history of the PR, so setuptools-scm can compute the correct version number
           fetch-depth: 0
 
-      - name: Install dependencies from APT
-        run: |
-          sudo apt-get update
-          sudo apt-get install -y just libopenmpi-dev openmpi-bin libboost-dev libboost-test-dev libmsgpack-cxx-dev libhwloc-dev
-
-      - name: Install the latest version of uv
-        uses: astral-sh/setup-uv@v10.0.1
+      - name: Set up the build environment
+        uses: ./.github/actions/setup
         with:
-          enable-cache: true
           cache-suffix: documentation
-          python-version: "3.11"
 
       - name: Set up Node.js
         uses: actions/setup-node@v7.0.0
@@ -74,11 +67,7 @@ jobs:
       - name: Check built docs links (including external)
         uses: lycheeverse/lychee-action@v2
         with:
-          args: >-
-            --config .lychee.postbuild.toml --no-progress
-            --root-dir ${{ github.workspace }}/docs/out
-            --fallback-extensions html
-            'docs/out/**/*.html'
+          args: "--config .lychee.postbuild.toml 'docs/out/**/*.html'"
           fail: true
 
       - name: Setup Pages