diff --git a/.github/actions/build-mpas/action.yml b/.github/actions/build-mpas/action.yml
new file mode 100644
index 0000000000..0db8a88847
--- /dev/null
+++ b/.github/actions/build-mpas/action.yml
@@ -0,0 +1,141 @@
+name: 'Build MPAS'
+description: 'Build MPAS-Atmosphere with specified compiler configuration'
+
+inputs:
+  compiler:
+    description: 'Compiler family (gcc, nvhpc, oneapi, etc.)'
+    required: true
+  use-pio:
+    description: 'Use PIO library (true/false)'
+    required: false
+    default: 'false'
+  openacc:
+    description: 'Enable OpenACC (true/false)'
+    required: false
+    default: 'false'
+  precision:
+    description: 'Floating-point precision (single or double)'
+    required: false
+    default: 'single'
+  build-timeout:
+    description: 'Build timeout in minutes'
+    required: false
+    default: '20'
+
+outputs:
+  executable:
+    description: 'Path to built executable'
+    value: ${{ steps.build.outputs.executable }}
+
+runs:
+  using: 'composite'
+  steps:
+    - name: Build MPAS-A
+      id: build
+      shell: bash
+      run: |
+        # Source container environment if available
+        # This sets NETCDF, PNETCDF, PIO, and other library paths
+        if [ -f /container/config_env.sh ]; then
+          echo "Sourcing container environment from /container/config_env.sh"
+          source /container/config_env.sh
+        fi
+
+        # MPAS Makefile uses `cpp` for Registry preprocessing.
+        # Some containers (e.g. openSUSE Leap) don't ship it separately.
+        if ! command -v cpp &>/dev/null; then
+          echo "cpp not found, installing..."
+          if command -v zypper &>/dev/null; then
+            zypper install -y --no-recommends cpp
+          elif command -v dnf &>/dev/null; then
+            dnf install -y cpp
+          elif command -v apt-get &>/dev/null; then
+            apt-get update && apt-get install -y cpp
+          fi
+        fi
+        
+        # Map compiler input to COMPILER_FAMILY if not already set
+        # The container should set this, but we provide a fallback
+        if [ -z "${COMPILER_FAMILY}" ]; then
+          case "${{ inputs.compiler }}" in
+            gcc|gfortran|gnu)   export COMPILER_FAMILY="gcc" ;;
+            nvhpc|nvfortran)    export COMPILER_FAMILY="nvhpc" ;;
+            oneapi|intel|ifx)   export COMPILER_FAMILY="oneapi" ;;
+            llvm|flang|clang)   export COMPILER_FAMILY="clang" ;;
+            *)                  export COMPILER_FAMILY="${{ inputs.compiler }}" ;;
+          esac
+        fi
+        
+        # Set up I/O configuration
+        if [ "${{ inputs.use-pio }}" = "true" ]; then
+          export PIO_ROOT=${PIO_ROOT:-/container/pio}
+          export USE_PIO2=true
+        else
+          unset PIO
+          export USE_PIO2=false
+        fi
+        
+        # Set up accelerator configuration
+        if [ "${{ inputs.openacc }}" = "true" ]; then
+          export OPENACC=true
+        fi
+        
+        echo "Build configuration:"
+        echo "  Compiler input: ${{ inputs.compiler }}"
+        echo "  COMPILER_FAMILY: ${COMPILER_FAMILY}"
+        echo "  NETCDF: ${NETCDF:-not set}"
+        echo "  PNETCDF: ${PNETCDF:-not set}"
+        echo "  USE_PIO2: ${USE_PIO2}"
+        echo "  OPENACC: ${OPENACC:-false}"
+        echo "  PRECISION: ${{ inputs.precision }}"
+        
+        # Settings from .github/ci-config.env — edit that file to change targets/workarounds
+        CI_CONFIG="${GITHUB_WORKSPACE}/.github/ci-config.env"
+        if [ -f "${CI_CONFIG}" ]; then
+          source "${CI_CONFIG}"
+        fi
+
+        # Map COMPILER_FAMILY to make target via ci-config.env lookup
+        VARNAME="MAKE_TARGET_${COMPILER_FAMILY}"
+        MAKE_TARGET="${!VARNAME}"
+        if [ -z "${MAKE_TARGET}" ]; then
+          echo "::error::No make target for COMPILER_FAMILY=${COMPILER_FAMILY}. Add MAKE_TARGET_${COMPILER_FAMILY}= to .github/ci-config.env"
+          exit 1
+        fi
+
+        EXTRA_MAKE_FLAGS=""
+        if [ "${COMPILER_FAMILY}" = "nvhpc" ]; then
+          ARCH="${NVHPC_TARGET_ARCH:--tp=px}"
+          sed -i "/^nvhpc:/,/^[a-z]/ s/\"FFLAGS_OPT = /\"FFLAGS_OPT = ${ARCH} /" Makefile
+          sed -i "/^nvhpc:/,/^[a-z]/ s/\"CFLAGS_OPT = /\"CFLAGS_OPT = ${ARCH} /" Makefile
+          sed -i "/^nvhpc:/,/^[a-z]/ s/\"CXXFLAGS_OPT = /\"CXXFLAGS_OPT = ${ARCH} /" Makefile
+          sed -i "/^nvhpc:/,/^[a-z]/ s/\"LDFLAGS_OPT = /\"LDFLAGS_OPT = ${ARCH} /" Makefile
+          EXTRA_MAKE_FLAGS="${NVHPC_EXTRA_MAKE_FLAGS}"
+        elif [ "${COMPILER_FAMILY}" = "oneapi" ]; then
+          EXTRA_MAKE_FLAGS="${ONEAPI_EXTRA_MAKE_FLAGS}"
+        fi
+
+        echo "  Make target: ${MAKE_TARGET}"
+        echo "  Extra make flags: ${EXTRA_MAKE_FLAGS:-<none>}"
+        echo "  Parallel jobs: ${MAKE_J_PROCS:-$(nproc)}"
+
+        PRECISION_FLAG=""
+        if [ "${{ inputs.precision }}" = "double" ]; then
+          PRECISION_FLAG="PRECISION=double"
+        fi
+
+        timeout ${{ inputs.build-timeout }}m \
+          make ${MAKE_TARGET} CORE=atmosphere ${EXTRA_MAKE_FLAGS} ${PRECISION_FLAG} --jobs ${MAKE_J_PROCS:-$(nproc)}
+        
+        # Set output
+        echo "executable=$(pwd)/atmosphere_model" >> $GITHUB_OUTPUT
+
+    - name: Verify executable
+      shell: bash
+      run: |
+        if [ ! -f atmosphere_model ]; then
+          echo "ERROR: atmosphere_model not found!"
+          exit 1
+        fi
+        ls -la atmosphere_model
+        file atmosphere_model
diff --git a/.github/actions/download-testdata/action.yml b/.github/actions/download-testdata/action.yml
new file mode 100644
index 0000000000..86d1457943
--- /dev/null
+++ b/.github/actions/download-testdata/action.yml
@@ -0,0 +1,97 @@
+name: 'Download Test Data'
+description: 'Download and extract an MPAS test case archive from GitHub releases'
+
+inputs:
+  resolution:
+    description: 'Test case resolution (e.g., 240km, 120km). Used to look up RELEASE_TESTDATA_{RES} in ci-config.env.'
+    required: true
+  dest-dir:
+    description: 'Destination directory name for the extracted test case'
+    required: false
+    default: ''
+
+outputs:
+  case-dir:
+    description: 'Path to the extracted test case directory'
+    value: ${{ steps.extract.outputs.case-dir }}
+
+runs:
+  using: composite
+  steps:
+    - name: Resolve release tag and archive
+      id: resolve
+      shell: bash
+      run: |
+        RESOLUTION="${{ inputs.resolution }}"
+        ARCHIVE="${RESOLUTION}.tar.gz"
+
+        CI_CONFIG="${GITHUB_WORKSPACE}/.github/ci-config.env"
+        if [ ! -f "${CI_CONFIG}" ]; then
+          echo "::error::ci-config.env not found at ${CI_CONFIG}"
+          exit 1
+        fi
+        source "${CI_CONFIG}"
+
+        RES_UPPER=$(echo "${RESOLUTION}" | tr '[:lower:]' '[:upper:]' | tr '-' '_')
+        TAG_VAR="RELEASE_TESTDATA_${RES_UPPER}"
+        TAG="${!TAG_VAR}"
+
+        if [ -z "${TAG}" ]; then
+          echo "::error::No release tag for resolution '${RESOLUTION}'. Add ${TAG_VAR}= to ci-config.env."
+          exit 1
+        fi
+
+        REPO="${DATA_REPOSITORY:-${GITHUB_REPOSITORY}}"
+        URL="https://github.com/${REPO}/releases/download/${TAG}/${ARCHIVE}"
+
+        echo "release-tag=${TAG}" >> $GITHUB_OUTPUT
+        echo "archive=${ARCHIVE}" >> $GITHUB_OUTPUT
+        echo "url=${URL}" >> $GITHUB_OUTPUT
+        echo "Resolved: ${TAG_VAR}=${TAG} → ${URL}"
+
+    - name: Cache test case archive
+      id: cache
+      uses: actions/cache@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5
+      with:
+        path: ${{ steps.resolve.outputs.archive }}
+        key: testdata-${{ steps.resolve.outputs.release-tag }}
+
+    - name: Download test case archive
+      if: steps.cache.outputs.cache-hit != 'true'
+      shell: bash
+      run: |
+        URL="${{ steps.resolve.outputs.url }}"
+        ARCHIVE="${{ steps.resolve.outputs.archive }}"
+        echo "Downloading ${ARCHIVE} from ${URL}..."
+        curl -fsSL --retry 5 --retry-delay 5 "${URL}" -o "${ARCHIVE}"
+        echo "Downloaded $(du -h "${ARCHIVE}" | cut -f1)"
+
+    - name: Extract test case
+      id: extract
+      shell: bash
+      run: |
+        ARCHIVE="${{ steps.resolve.outputs.archive }}"
+        DEST="${{ inputs.dest-dir }}"
+
+        echo "Cache hit: ${{ steps.cache.outputs.cache-hit }}"
+        echo "Archive: ${ARCHIVE} ($(du -h "${ARCHIVE}" | cut -f1))"
+
+        tar xzf "${ARCHIVE}"
+
+        CASE_DIR=$(tar tzf "${ARCHIVE}" 2>/dev/null | head -1 | cut -d/ -f1 || true)
+        if [ -z "${CASE_DIR}" ]; then
+          CASE_DIR=$(ls -td */ 2>/dev/null | head -1 | tr -d '/')
+        fi
+
+        if [ -z "${CASE_DIR}" ] || [ ! -d "${CASE_DIR}" ]; then
+          echo "::error::Failed to extract test case from ${ARCHIVE}"
+          exit 1
+        fi
+
+        if [ -n "${DEST}" ] && [ "${DEST}" != "${CASE_DIR}" ]; then
+          mv "${CASE_DIR}" "${DEST}"
+          CASE_DIR="${DEST}"
+        fi
+
+        echo "case-dir=${CASE_DIR}" >> $GITHUB_OUTPUT
+        echo "Extracted test case to: ${CASE_DIR}"
diff --git a/.github/actions/ect-summary/action.yml b/.github/actions/ect-summary/action.yml
new file mode 100644
index 0000000000..6175f5a33a
--- /dev/null
+++ b/.github/actions/ect-summary/action.yml
@@ -0,0 +1,100 @@
+name: 'ECT Summary'
+description: >
+  Generate a consolidated Ensemble Consistency Test results table from
+  enriched result files produced by the validate-ect action. Writes a
+  Markdown table to $GITHUB_STEP_SUMMARY with auto-discovered columns.
+
+inputs:
+  results-path:
+    description: 'Directory containing downloaded ect-result-* artifact subdirectories'
+    required: true
+
+runs:
+  using: 'composite'
+  steps:
+    - name: Generate summary table
+      shell: bash
+      run: |
+        RESULTS_PATH="${{ inputs.results-path }}"
+
+        # Collect all result files
+        RESULT_FILES=()
+        for f in "${RESULTS_PATH}"/ect-result-*/ect-result.txt; do
+          [ -f "$f" ] && RESULT_FILES+=("$f")
+        done
+
+        if [ ${#RESULT_FILES[@]} -eq 0 ]; then
+          echo "::warning::No ECT result files found in ${RESULTS_PATH}"
+          echo "## Ensemble Consistency Test (ECT) Results" >> "$GITHUB_STEP_SUMMARY"
+          echo "" >> "$GITHUB_STEP_SUMMARY"
+          echo "No results available." >> "$GITHUB_STEP_SUMMARY"
+          exit 0
+        fi
+
+        # Discover column names from the first result file (all keys except "result")
+        COLUMNS=()
+        while IFS='=' read -r key value; do
+          [ -z "$key" ] && continue
+          if [ "$key" != "result" ]; then
+            COLUMNS+=("$key")
+          fi
+        done < "${RESULT_FILES[0]}"
+
+        # Build header row
+        HEADER="| "
+        SEPARATOR="| "
+        for col in "${COLUMNS[@]}"; do
+          COL_TITLE=$(echo "$col" | sed 's/.*/\u&/')
+          HEADER+="${COL_TITLE} | "
+          SEPARATOR+="--- | "
+        done
+        HEADER+="Result |"
+        SEPARATOR+="--- |"
+
+        # Build data rows
+        PASS=0 FAIL=0 ERROR=0 SKIP=0 TOTAL=0
+        ROWS=""
+        for f in "${RESULT_FILES[@]}"; do
+          TOTAL=$((TOTAL + 1))
+
+          # Parse key=value pairs
+          declare -A DATA=()
+          while IFS='=' read -r key value; do
+            [ -z "$key" ] && continue
+            DATA["$key"]="$value"
+          done < "$f"
+
+          RESULT="${DATA[result]}"
+          case "$RESULT" in
+            PASSED)  ICON="PASSED"; PASS=$((PASS + 1)) ;;
+            FAILED)  ICON="**FAILED**"; FAIL=$((FAIL + 1)) ;;
+            SKIPPED) ICON="SKIPPED"; SKIP=$((SKIP + 1)) ;;
+            *)       ICON="ERROR"; ERROR=$((ERROR + 1)) ;;
+          esac
+
+          ROW="| "
+          for col in "${COLUMNS[@]}"; do
+            ROW+="${DATA[$col]:-—} | "
+          done
+          ROW+="${ICON} |"
+          ROWS+="${ROW}"$'\n'
+
+          unset DATA
+        done
+
+        SORTED_ROWS=$(echo "$ROWS" | sort)
+
+        {
+          echo "## Ensemble Consistency Test (ECT) Results"
+          echo ""
+          echo "$HEADER"
+          echo "$SEPARATOR"
+          echo "$SORTED_ROWS"
+          echo ""
+          echo "**Total: ${TOTAL}** — ${PASS} passed, ${FAIL} failed, ${ERROR} error, ${SKIP} skipped"
+
+          if [ ${FAIL} -gt 0 ] || [ ${ERROR} -gt 0 ]; then
+            echo ""
+            echo "> One or more ECT validations failed. Check individual ECT Validate job logs for PyCECT details."
+          fi
+        } >> "$GITHUB_STEP_SUMMARY"
diff --git a/.github/actions/mpas-version/action.yml b/.github/actions/mpas-version/action.yml
new file mode 100644
index 0000000000..73c3b3e47a
--- /dev/null
+++ b/.github/actions/mpas-version/action.yml
@@ -0,0 +1,47 @@
+name: 'Get MPAS Version'
+description: >
+  Read the MPAS version string from src/core_atmosphere/Registry.xml.
+  Strict — fails the workflow if the file is missing or the version
+  attribute cannot be parsed (no silent "unknown" fallback).
+
+inputs:
+  registry-path:
+    description: 'Path to Registry.xml relative to GITHUB_WORKSPACE'
+    required: false
+    default: 'src/core_atmosphere/Registry.xml'
+
+outputs:
+  version:
+    description: 'MPAS version string (e.g., 8.4.0)'
+    value: ${{ steps.extract.outputs.version }}
+
+runs:
+  using: 'composite'
+  steps:
+    - id: extract
+      shell: bash
+      run: |
+        python3 - "${{ inputs.registry-path }}" <<'PYEOF'
+        import os
+        import sys
+        import xml.etree.ElementTree as ET
+
+        path = sys.argv[1]
+        if not os.path.isfile(path):
+            print(f"::error::MPAS Registry not found at {path}")
+            sys.exit(1)
+        try:
+            root = ET.parse(path).getroot()
+        except ET.ParseError as e:
+            print(f"::error::Could not parse {path}: {e}")
+            sys.exit(1)
+
+        version = root.attrib.get('version')
+        if not version:
+            print(f"::error::No version attribute on <registry> in {path}")
+            sys.exit(1)
+
+        with open(os.environ['GITHUB_OUTPUT'], 'a') as f:
+            f.write(f"version={version}\n")
+        print(f"MPAS version: {version}")
+        PYEOF
diff --git a/.github/actions/print-mpas-logs/action.yml b/.github/actions/print-mpas-logs/action.yml
new file mode 100644
index 0000000000..53ed7e33b1
--- /dev/null
+++ b/.github/actions/print-mpas-logs/action.yml
@@ -0,0 +1,64 @@
+name: 'Print MPAS Logs'
+description: >
+  Print MPAS per-rank log files (log.atmosphere.<rank>.out / .err) to the
+  workflow log inside collapsible ::group:: blocks. Read-only; never fails
+  on its own (use if: always() at the call site).
+
+inputs:
+  log-dir:
+    description: 'Directory to scan for log files'
+    required: true
+  pattern:
+    description: >
+      Glob (relative to log-dir) of files to print. Default catches both
+      .out and .err per rank.
+    required: false
+    default: 'log.atmosphere.*'
+  max-lines:
+    description: >
+      If set, print only the last N lines of each file via tail. Empty (default)
+      prints the whole file.
+    required: false
+    default: ''
+
+runs:
+  using: 'composite'
+  steps:
+    - name: Print logs
+      shell: bash
+      run: |
+        LOG_DIR="${{ inputs.log-dir }}"
+        PATTERN="${{ inputs.pattern }}"
+        MAX_LINES="${{ inputs.max-lines }}"
+
+        if [ ! -d "${LOG_DIR}" ]; then
+          echo "print-mpas-logs: directory '${LOG_DIR}' does not exist; nothing to print."
+          exit 0
+        fi
+
+        cd "${LOG_DIR}"
+        shopt -s nullglob
+
+        # Sort so .out comes before .err per rank (lexical order does this).
+        FILES=( $(ls -1 ${PATTERN} 2>/dev/null | sort) )
+
+        if [ ${#FILES[@]} -eq 0 ]; then
+          echo "print-mpas-logs: no files matching '${PATTERN}' in ${LOG_DIR}."
+          exit 0
+        fi
+
+        echo "print-mpas-logs: ${#FILES[@]} file(s) from ${LOG_DIR}"
+        # Close the implicit group GitHub opens for the run: script source so
+        # the per-file groups below render at the step's top level (collapsible
+        # at normal font size) instead of nested inside the script-source group.
+        echo "::endgroup::"
+        for f in "${FILES[@]}"; do
+          echo "::group::${f}"
+          if [ -n "${MAX_LINES}" ]; then
+            echo "(last ${MAX_LINES} lines)"
+            tail -n "${MAX_LINES}" "${f}" || true
+          else
+            cat "${f}" || true
+          fi
+          echo "::endgroup::"
+        done
diff --git a/.github/actions/resolve-container/action.yml b/.github/actions/resolve-container/action.yml
new file mode 100644
index 0000000000..fccafffd76
--- /dev/null
+++ b/.github/actions/resolve-container/action.yml
@@ -0,0 +1,65 @@
+name: 'Resolve Container Image'
+description: 'Assemble a container image name from ci-config.env templates'
+
+inputs:
+  compiler:
+    description: 'Compiler family (gcc, nvhpc, oneapi)'
+    required: true
+  mpi:
+    description: 'MPI implementation (openmpi, mpich)'
+    required: true
+  gpu:
+    description: 'GPU variant (empty string, or "cuda")'
+    required: false
+    default: ''
+
+outputs:
+  image:
+    description: 'Fully qualified container image name'
+    value: ${{ steps.resolve.outputs.image }}
+
+runs:
+  using: 'composite'
+  steps:
+    - name: Resolve container image
+      id: resolve
+      shell: bash
+      run: |
+        CI_CONFIG="${GITHUB_WORKSPACE}/.github/ci-config.env"
+        if [ ! -f "${CI_CONFIG}" ]; then
+          echo "::error::ci-config.env not found at ${CI_CONFIG}"
+          exit 1
+        fi
+        source "${CI_CONFIG}"
+
+        COMPILER="${{ inputs.compiler }}"
+        MPI="${{ inputs.mpi }}"
+        GPU="${{ inputs.gpu }}"
+
+        # Resolve compiler name (fallback to raw value if no mapping)
+        comp_var="CONTAINER_COMPILER_${COMPILER}"
+        COMPILER_NAME="${!comp_var:-$COMPILER}"
+
+        # Resolve MPI name (fallback to raw value if no mapping)
+        mpi_var="CONTAINER_MPI_${MPI}"
+        MPI_NAME="${!mpi_var:-$MPI}"
+
+        # Pick template: GPU vs CPU, then check for per-compiler override
+        if [ -n "${GPU}" ]; then
+          gpu_override="CONTAINER_IMAGE_GPU_${COMPILER}"
+          TEMPLATE="${!gpu_override:-$CONTAINER_IMAGE_GPU}"
+        else
+          cpu_override="CONTAINER_IMAGE_${COMPILER}"
+          TEMPLATE="${!cpu_override:-$CONTAINER_IMAGE}"
+        fi
+
+        # Substitute placeholders
+        IMAGE="${TEMPLATE//\{compiler\}/$COMPILER_NAME}"
+        IMAGE="${IMAGE//\{mpi\}/$MPI_NAME}"
+
+        echo "Resolved container image: ${IMAGE}"
+        echo "  Compiler:  ${COMPILER} → ${COMPILER_NAME}"
+        echo "  MPI:       ${MPI} → ${MPI_NAME}"
+        echo "  GPU:       ${GPU:-none}"
+
+        echo "image=${IMAGE}" >> $GITHUB_OUTPUT
diff --git a/.github/actions/run-mpas/action.yml b/.github/actions/run-mpas/action.yml
new file mode 100644
index 0000000000..063697a90b
--- /dev/null
+++ b/.github/actions/run-mpas/action.yml
@@ -0,0 +1,195 @@
+name: 'Run MPAS'
+description: 'Run MPAS-Atmosphere test case'
+
+inputs:
+  executable:
+    description: 'Path to atmosphere_model executable'
+    required: false
+    default: './atmosphere_model'
+  num-procs:
+    description: 'Number of MPI processes'
+    required: false
+    default: '1'
+  run-duration:
+    description: 'Run duration (format: D_HH:MM:SS). If empty, uses the namelist default from the test case archive.'
+    required: false
+    default: ''
+  restart-interval:
+    description: 'Restart output interval (format: D_HH:MM:SS). If empty, uses the streams.atmosphere default.'
+    required: false
+    default: ''
+  resolution:
+    description: 'Test case resolution name (e.g., 240km). Used to download the archive and name the working directory.'
+    required: false
+    default: '240km'
+  mpi-impl:
+    description: 'MPI implementation (openmpi, mpich)'
+    required: false
+    default: ''
+  run-timeout:
+    description: 'Run timeout in minutes'
+    required: false
+    default: '20'
+  working-dir:
+    description: 'Working directory name for the run'
+    required: false
+    default: ''
+  strict-exit-check:
+    description: 'Fail on non-zero exit code (default true). Set false when gfortran IEEE warnings produce non-zero exit but model output is valid.'
+    required: false
+    default: 'true'
+
+outputs:
+  log-dir:
+    description: 'Directory containing log files'
+    value: ${{ steps.run.outputs.log-dir }}
+  status:
+    description: 'Run status (success/failed)'
+    value: ${{ steps.run.outputs.status }}
+
+runs:
+  using: 'composite'
+  steps:
+    - name: Resolve configuration
+      id: config
+      shell: bash
+      run: |
+        RESOLUTION="${{ inputs.resolution }}"
+        WORKDIR="${{ inputs.working-dir }}"
+        if [ -z "${WORKDIR}" ]; then
+          WORKDIR="run-${RESOLUTION}"
+        fi
+
+        echo "workdir=${WORKDIR}" >> $GITHUB_OUTPUT
+        echo "resolution=${RESOLUTION}" >> $GITHUB_OUTPUT
+
+        echo "=== Run configuration ==="
+        echo "  Resolution: ${RESOLUTION}"
+        echo "  Work dir:   ${WORKDIR}"
+        echo "  Timeout:    ${{ inputs.run-timeout }}m"
+        if [ -n "${{ inputs.run-duration }}" ]; then
+          echo "  Duration:   ${{ inputs.run-duration }} (override)"
+        else
+          echo "  Duration:   (namelist default)"
+        fi
+
+    - name: Download test case
+      uses: ./.github/actions/download-testdata
+      id: download
+      with:
+        resolution: ${{ inputs.resolution }}
+        dest-dir: ${{ steps.config.outputs.workdir }}
+
+    - name: Link executable
+      shell: bash
+      run: |
+        WORKDIR="${{ steps.config.outputs.workdir }}"
+        chmod +x ${{ inputs.executable }}
+        ln -sf $(realpath ${{ inputs.executable }}) "${WORKDIR}/atmosphere_model"
+
+    - name: Configure namelist overrides
+      shell: bash
+      working-directory: ${{ steps.config.outputs.workdir }}
+      run: |
+        if [ -n "${{ inputs.run-duration }}" ]; then
+          DURATION="${{ inputs.run-duration }}"
+          sed -i "s/config_run_duration = '[^']*'/config_run_duration = '${DURATION}'/" namelist.atmosphere
+          echo "Overrode config_run_duration = '${DURATION}'"
+        fi
+
+        if [ -n "${{ inputs.restart-interval }}" ]; then
+          RESTART="${{ inputs.restart-interval }}"
+          sed -i '/<immutable_stream name="restart"/,/\/>/ s/output_interval="[^"]*"/output_interval="'"${RESTART}"'"/' streams.atmosphere
+          echo "Overrode restart output_interval = '${RESTART}'"
+        fi
+
+        echo "=== Namelist ==="
+        grep config_run_duration namelist.atmosphere
+
+    - name: Run MPAS-A
+      id: run
+      shell: bash
+      working-directory: ${{ steps.config.outputs.workdir }}
+      run: |
+        TIMEOUT="${{ inputs.run-timeout }}"
+
+        if [ -f /container/config_env.sh ]; then
+          source /container/config_env.sh
+        fi
+
+        # Workaround: some containers omit LD_LIBRARY_PATH from config_env.sh
+        if [ -z "${LD_LIBRARY_PATH}" ]; then
+          export LD_LIBRARY_PATH="/usr/lib64:/usr/lib"
+        fi
+
+        if [ -n "${{ inputs.mpi-impl }}" ]; then
+          export MPI_IMPL="${{ inputs.mpi-impl }}"
+        fi
+
+        CI_CONFIG="${GITHUB_WORKSPACE}/.github/ci-config.env"
+        if [ -f "${CI_CONFIG}" ]; then
+          source "${CI_CONFIG}"
+        fi
+
+        MPI_FLAGS=""
+        if [ "${MPI_IMPL}" = "openmpi" ]; then
+          MPI_FLAGS="${OPENMPI_RUN_FLAGS:---allow-run-as-root --oversubscribe}"
+        fi
+
+        ulimit -s unlimited 2>/dev/null || echo "Warning: Could not set unlimited stack size"
+
+        echo "=== Run configuration ==="
+        echo "  Resolution: ${{ steps.config.outputs.resolution }}"
+        echo "  Processors: ${{ inputs.num-procs }}"
+        echo "  MPI_IMPL: ${MPI_IMPL:-auto}"
+        echo "  MPI_FLAGS: ${MPI_FLAGS}"
+        echo "  Stack limit: $(ulimit -s)"
+        echo "  Available CPUs: $(nproc 2>/dev/null || echo unknown)"
+        echo "  Available RAM: $(free -m 2>/dev/null | awk '/^Mem:/{print $2 "MB"}' || echo unknown)"
+        echo "  LD_LIBRARY_PATH: ${LD_LIBRARY_PATH:-not set}"
+
+        set +e
+        timeout ${TIMEOUT}m mpirun -n ${{ inputs.num-procs }} ${MPI_FLAGS} ./atmosphere_model
+        RUN_STATUS=$?
+        set -e
+
+        echo "log-dir=$(pwd)" >> $GITHUB_OUTPUT
+        echo "run-exit-code=${RUN_STATUS}" >> $GITHUB_OUTPUT
+        if [ $RUN_STATUS -eq 0 ]; then
+          echo "status=success" >> $GITHUB_OUTPUT
+        elif [ "${{ inputs.strict-exit-check }}" = "false" ]; then
+          echo "status=success" >> $GITHUB_OUTPUT
+          echo "::warning::Model exited with status ${RUN_STATUS} (non-strict mode, treating as success)"
+        else
+          echo "status=failed" >> $GITHUB_OUTPUT
+          echo "::warning::Model run exited with status $RUN_STATUS"
+        fi
+
+    - name: List output files
+      shell: bash
+      if: always()
+      run: |
+        WORKDIR="${{ steps.config.outputs.workdir }}"
+        echo "=== Output files ==="
+        if [ -d "${WORKDIR}" ]; then
+          cd "${WORKDIR}"
+          ls -la log.* 2>/dev/null || echo "No log files found"
+          ls -la *.nc 2>/dev/null || echo "No NetCDF files found"
+        else
+          echo "Working directory ${WORKDIR} does not exist"
+        fi
+
+    - name: Print MPAS logs
+      if: always()
+      uses: ./.github/actions/print-mpas-logs
+      with:
+        log-dir: ${{ steps.config.outputs.workdir }}
+
+    - name: Check run status
+      shell: bash
+      if: always()
+      run: |
+        if [ "${{ steps.run.outputs.status }}" = "failed" ]; then
+          echo "::error::MPAS model run failed with exit code ${{ steps.run.outputs.run-exit-code }}"
+          exit 1
+        fi
diff --git a/.github/actions/run-perturb-mpas/action.yml b/.github/actions/run-perturb-mpas/action.yml
new file mode 100644
index 0000000000..9af1660708
--- /dev/null
+++ b/.github/actions/run-perturb-mpas/action.yml
@@ -0,0 +1,284 @@
+name: 'Run Perturbed MPAS'
+description: >
+  Run one or more perturbed MPAS-A ensemble members for ECT.
+  Handles IC perturbation, namelist/stream configuration, model execution,
+  and optional history file trimming. Supports both single-member
+  (ect-test) and batched (ect-ensemble-gen) use cases.
+
+inputs:
+  base-dir:
+    description: 'Path to the base test case directory (copied per member)'
+    required: true
+  executable:
+    description: 'Path to atmosphere_model executable'
+    required: true
+  member-start:
+    description: 'First ensemble member index'
+    required: true
+  member-end:
+    description: 'Last ensemble member index (same as member-start for single member)'
+    required: true
+  run-duration:
+    description: 'Model run duration per member (format: D_HH:MM:SS)'
+    required: true
+  run-timeout:
+    description: 'Per-member timeout in minutes'
+    required: false
+    default: '45'
+  num-ranks:
+    description: 'Number of MPI ranks per member'
+    required: false
+    default: '1'
+  mpi-impl:
+    description: 'MPI implementation (openmpi, mpich)'
+    required: false
+    default: 'openmpi'
+  output-dir:
+    description: 'Directory to collect trimmed history files'
+    required: false
+    default: 'history-output'
+  trim:
+    description: 'Trim history files after run (true/false)'
+    required: false
+    default: 'true'
+  restart-file:
+    description: 'Path to a spun-up restart file. When set, each member starts from this restart (with config_do_restart=.true.) instead of init.nc.'
+    required: false
+    default: ''
+  verbose:
+    description: 'Print detailed diagnostics for each member (namelist dumps, theta stats)'
+    required: false
+    default: 'false'
+
+outputs:
+  status:
+    description: 'Overall status (success/partial/failed)'
+    value: ${{ steps.run-members.outputs.status }}
+  members-completed:
+    description: 'Number of members that produced history files'
+    value: ${{ steps.run-members.outputs.members-completed }}
+
+runs:
+  using: 'composite'
+  steps:
+    - name: Run perturbed members
+      id: run-members
+      shell: bash
+      run: |
+        source /container/config_env.sh
+
+        if command -v conda &>/dev/null; then
+          eval "$(conda shell.bash hook)" 2>/dev/null
+          conda activate base 2>/dev/null || true
+        fi
+
+        if ! python3 -c "import netCDF4, numpy" 2>/dev/null; then
+          if python3 -m pip install --quiet netCDF4 numpy 2>/dev/null; then
+            echo "Installed netCDF4/numpy via pip"
+          elif command -v conda &>/dev/null; then
+            conda install -y -q netCDF4 numpy
+            echo "Installed netCDF4/numpy via conda"
+          else
+            echo "::error::Could not install netCDF4 (no pip, no conda)"
+            exit 1
+          fi
+        fi
+        echo "python3: $(which python3) — $(python3 --version)"
+
+        if [ -z "${LD_LIBRARY_PATH}" ]; then
+          export LD_LIBRARY_PATH="/usr/lib64:/usr/lib"
+        fi
+
+        CI_CONFIG="${GITHUB_WORKSPACE}/.github/ci-config.env"
+        if [ -f "${CI_CONFIG}" ]; then
+          source "${CI_CONFIG}"
+        fi
+        ulimit -s unlimited 2>/dev/null || true
+
+        BASEDIR="${{ inputs.base-dir }}"
+        EXE="${{ inputs.executable }}"
+        MEMBER_START=${{ inputs.member-start }}
+        MEMBER_END=${{ inputs.member-end }}
+        NRANKS=${{ inputs.num-ranks }}
+        MPI_IMPL="${{ inputs.mpi-impl }}"
+        OUTDIR="${{ inputs.output-dir }}"
+        TRIM="${{ inputs.trim }}"
+        RESTART_FILE="${{ inputs.restart-file }}"
+        VERBOSE="${{ inputs.verbose }}"
+        RUN_DURATION="${{ inputs.run-duration }}"
+        RUN_TIMEOUT="${{ inputs.run-timeout }}"
+
+        MPI_FLAGS=""
+        if [ "${MPI_IMPL}" = "openmpi" ]; then
+          MPI_FLAGS="${OPENMPI_RUN_FLAGS:---allow-run-as-root --oversubscribe}"
+        fi
+
+        EXCLUDE_FILE=""
+        if [ -n "${ECT_EXCLUDED_VARS}" ]; then
+          EXCLUDE_FILE="${GITHUB_WORKSPACE}/${ECT_EXCLUDED_VARS}"
+        fi
+
+        mkdir -p "${OUTDIR}"
+
+        TOTAL=0
+        COMPLETED=0
+
+        for MEMBER in $(seq ${MEMBER_START} ${MEMBER_END}); do
+          TOTAL=$((TOTAL + 1))
+          MEMBER_ID=$(printf "%04d" ${MEMBER})
+          RUNDIR="run-ect-${MEMBER_ID}"
+          echo ""
+          echo "=========================================="
+          echo "  Ensemble member ${MEMBER_ID}"
+          echo "=========================================="
+
+          cp -r "${BASEDIR}" "${RUNDIR}"
+          chmod +x "${EXE}"
+          ln -sf $(realpath "${EXE}") "${RUNDIR}/atmosphere_model"
+
+          if [ -n "${RESTART_FILE}" ]; then
+            RESTART_TIME=$(python3 -c "
+        import netCDF4, sys
+        ds = netCDF4.Dataset(sys.argv[1])
+        print(ds.variables['xtime'][0].tobytes().decode().strip())
+        ds.close()
+        " "${RESTART_FILE}")
+            RESTART_FNAME="restart.$(echo ${RESTART_TIME} | tr ':' '.').nc"
+            cp "${RESTART_FILE}" "${RUNDIR}/${RESTART_FNAME}"
+            echo "${RESTART_TIME}" > "${RUNDIR}/restart_timestamp"
+            PERTURB_FILE="${RUNDIR}/${RESTART_FNAME}"
+            echo "[$(date +%H:%M:%S)] Restart mode: ${RESTART_FNAME} (time=${RESTART_TIME})"
+          else
+            PERTURB_FILE="${RUNDIR}/init.nc"
+            if [ ! -f "${PERTURB_FILE}" ]; then
+              PERTURB_FILE=$(ls ${RUNDIR}/*.init*.nc 2>/dev/null | head -1)
+            fi
+          fi
+
+          if [ -z "${PERTURB_FILE}" ] || [ ! -f "${PERTURB_FILE}" ]; then
+            echo "::error::Member ${MEMBER_ID}: could not find file to perturb"
+            rm -rf "${RUNDIR}"
+            continue
+          fi
+
+          echo "[$(date +%H:%M:%S)] Perturbing theta (seed=${MEMBER})..."
+          python3 ${GITHUB_WORKSPACE}/.github/actions/run-perturb-mpas/perturb_theta.py \
+            "${PERTURB_FILE}" --seed ${MEMBER} --magnitude ${ECT_PERTURB_MAGNITUDE}
+
+          if [ "${VERBOSE}" = "true" ]; then
+            echo "  Restart MD5: $(md5sum "${PERTURB_FILE}" | cut -d' ' -f1)"
+          fi
+
+          cd "${RUNDIR}"
+
+          if [ -n "${RESTART_FILE}" ]; then
+            sed -i "s/config_do_restart.*/config_do_restart = .true./" namelist.atmosphere
+            sed -i "s/config_start_time.*/config_start_time = 'file'/" namelist.atmosphere
+            sed -i '/&restart/a\    config_do_DAcycling = .true.' namelist.atmosphere
+          fi
+
+          sed -i "s/config_run_duration = '[^']*'/config_run_duration = '${RUN_DURATION}'/" namelist.atmosphere
+          sed -i '/<immutable_stream name="restart"/,/\/>/ s/output_interval="[^"]*"/output_interval="none"/' streams.atmosphere
+          sed -i '/<stream name="output"/,/>/ s/output_interval="[^"]*"/output_interval="'"${RUN_DURATION}"'"/' streams.atmosphere
+
+          echo "[$(date +%H:%M:%S)] Running MPAS-A (${RUN_DURATION}, ${NRANKS} ranks)..."
+          set +e
+          timeout ${RUN_TIMEOUT}m mpirun -n ${NRANKS} ${MPI_FLAGS} ./atmosphere_model
+          RUN_STATUS=$?
+          set -e
+          echo "[$(date +%H:%M:%S)] Model finished (exit code ${RUN_STATUS})"
+
+          for LOGFILE in log.atmosphere.*.out log.atmosphere.*.err; do
+            [ -f "${LOGFILE}" ] || continue
+            EXT="${LOGFILE##*.}"
+            BASE="${LOGFILE%.*}"
+            cp "${LOGFILE}" "../${OUTDIR}/${BASE}.member${MEMBER_ID}.${EXT}"
+          done
+
+          if [ "${VERBOSE}" = "true" ]; then
+            echo "[$(date +%H:%M:%S)] === Namelist config ==="
+            grep -E 'config_do_restart|config_start_time|config_run_duration' namelist.atmosphere || true
+            echo "[$(date +%H:%M:%S)] === Restart stream ==="
+            grep -A2 'immutable_stream name="restart"' streams.atmosphere || true
+            echo "[$(date +%H:%M:%S)] === Output stream ==="
+            grep -A2 'stream name="output"' streams.atmosphere || true
+
+            RESTART_NC=$(ls restart.*.nc 2>/dev/null | head -1)
+            if [ -n "${RESTART_NC}" ]; then
+              echo "[$(date +%H:%M:%S)] === Restart theta check ==="
+              python3 -c "
+        import netCDF4 as nc, numpy as np, sys
+        ds = nc.Dataset(sys.argv[1])
+        th = ds.variables['theta'][:]
+        print(f'  File: {sys.argv[1]}')
+        print(f'  theta dtype={th.dtype} shape={th.shape} mean={np.mean(th):.15e}')
+        ds.close()
+        " "${RESTART_NC}"
+            fi
+          fi
+
+          echo "[$(date +%H:%M:%S)] History files produced:"
+          ls -la history.*.nc 2>/dev/null || echo "  (none)"
+          HIST_FILE=$(ls -t history.*.nc 2>/dev/null | head -1 || true)
+          if [ -n "${HIST_FILE}" ]; then
+            if [ "${VERBOSE}" = "true" ]; then
+              echo "[$(date +%H:%M:%S)] === History theta check ==="
+              python3 -c "
+        import netCDF4 as nc, numpy as np, sys
+        ds = nc.Dataset(sys.argv[1])
+        if 'theta' in ds.variables:
+            th = ds.variables['theta']
+            data = th[:]
+            print(f'  theta dtype={data.dtype} shape={data.shape} mean={np.mean(data):.15e} min={np.min(data):.10e} max={np.max(data):.10e}')
+        else:
+            print('  theta NOT in history variables')
+            print(f'  Available: {list(ds.variables.keys())[:15]}...')
+        ds.close()
+        " "${HIST_FILE}"
+            fi
+            TSLICE=$(python3 -c "
+        import netCDF4, sys
+        ds = netCDF4.Dataset(sys.argv[1])
+        print(ds.dimensions['Time'].size - 1)
+        ds.close()
+        " "${HIST_FILE}")
+            echo "[$(date +%H:%M:%S)] Using tslice=${TSLICE} (last time slice)"
+            if [ "${TRIM}" = "true" ] && [ -n "${EXCLUDE_FILE}" ] && [ -f "${EXCLUDE_FILE}" ]; then
+              python3 ${GITHUB_WORKSPACE}/.github/actions/run-perturb-mpas/trim_history.py \
+                "${HIST_FILE}" "../${OUTDIR}/history.${MEMBER_ID}.nc" \
+                --tslice ${TSLICE} \
+                --exclude-file "${EXCLUDE_FILE}"
+              echo "[$(date +%H:%M:%S)] Saved trimmed history for member ${MEMBER_ID}"
+            else
+              cp "${HIST_FILE}" "../${OUTDIR}/history.${MEMBER_ID}.nc"
+              echo "[$(date +%H:%M:%S)] Saved history for member ${MEMBER_ID}"
+            fi
+            COMPLETED=$((COMPLETED + 1))
+          else
+            echo "::warning::Member ${MEMBER_ID} failed (exit ${RUN_STATUS}, no history file)"
+          fi
+
+          cd ..
+          rm -rf "${RUNDIR}"
+        done
+
+        echo ""
+        echo "=== Completed ${COMPLETED}/${TOTAL} members ==="
+        ls -la "${OUTDIR}/"
+
+        echo "members-completed=${COMPLETED}" >> $GITHUB_OUTPUT
+        if [ ${COMPLETED} -eq ${TOTAL} ]; then
+          echo "status=success" >> $GITHUB_OUTPUT
+        elif [ ${COMPLETED} -gt 0 ]; then
+          echo "status=partial" >> $GITHUB_OUTPUT
+        else
+          echo "status=failed" >> $GITHUB_OUTPUT
+          echo "::error::No ensemble members produced history files"
+          exit 1
+        fi
+
+    - name: Print MPAS logs
+      if: always()
+      uses: ./.github/actions/print-mpas-logs
+      with:
+        log-dir: ${{ inputs.output-dir }}
diff --git a/.github/actions/run-perturb-mpas/perturb_theta.py b/.github/actions/run-perturb-mpas/perturb_theta.py
new file mode 100644
index 0000000000..62ab4520f7
--- /dev/null
+++ b/.github/actions/run-perturb-mpas/perturb_theta.py
@@ -0,0 +1,81 @@
+#!/usr/bin/env python3
+"""
+Apply O(10^-14) perturbation to the theta (potential temperature) field
+in an MPAS initial conditions file to generate ensemble diversity.
+
+This is a placeholder until native perturbation support is added to MPAS-A.
+Each ensemble member uses a unique seed for reproducible perturbations.
+"""
+
+import argparse
+import sys
+
+import numpy as np
+
+try:
+    from netCDF4 import Dataset
+except ImportError:
+    print("ERROR: netCDF4 is required. Install with: pip install netCDF4")
+    sys.exit(1)
+
+
+def perturb_theta(ic_file, seed, magnitude=1e-14):
+    rng = np.random.default_rng(seed)
+
+    with Dataset(ic_file, "r+") as ds:
+        if "theta" not in ds.variables:
+            print(f"ERROR: 'theta' variable not found in {ic_file}")
+            print(f"  Available variables: {list(ds.variables.keys())[:20]}...")
+            sys.exit(1)
+
+        theta = ds.variables["theta"]
+        data = theta[:]
+        original_mean = float(np.mean(data))
+
+        perturbation = rng.uniform(-magnitude, magnitude, size=data.shape)
+        theta[:] = data * (1.0 + perturbation)
+
+        actual_max = np.max(np.abs(perturbation))
+        print(f"Applied perturbation to theta field:")
+        print(f"  File:      {ic_file}")
+        print(f"  Format:    {ds.data_model}")
+        print(f"  Seed:      {seed}")
+        print(f"  Magnitude: +/- {magnitude:.0e}")
+        print(f"  Max |eps|: {actual_max:.2e}")
+        print(f"  Shape:     {data.shape}")
+        print(f"  Var dtype: {theta.dtype}")
+        print(f"  Original mean: {original_mean:.15e}")
+
+    # Read-back verification: reopen and confirm perturbation persisted
+    with Dataset(ic_file, "r") as ds:
+        verify = ds.variables["theta"][:]
+        verify_mean = float(np.mean(verify))
+        diff = verify.astype(np.float64) - data.astype(np.float64)
+        n_changed = int(np.count_nonzero(diff))
+        max_diff = float(np.max(np.abs(diff)))
+        print(f"  Verify mean:   {verify_mean:.15e}")
+        print(f"  Changed cells: {n_changed}/{diff.size}")
+        print(f"  Max |diff|:    {max_diff:.6e}")
+        if n_changed == 0:
+            print(f"ERROR: Perturbation did NOT persist in file!")
+            print(f"  On-disk dtype: {ds.variables['theta'].dtype}")
+            print(f"  If dtype is float32, perturbations below ~1.2e-7 will be rounded away.")
+            sys.exit(1)
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description="Perturb MPAS theta field for ensemble generation"
+    )
+    parser.add_argument("ic_file", help="Path to MPAS initial conditions NetCDF file")
+    parser.add_argument("--seed", type=int, required=True,
+                        help="Random seed for reproducible perturbation")
+    parser.add_argument("--magnitude", type=float, default=1e-14,
+                        help="Perturbation magnitude (default: 1e-14)")
+    args = parser.parse_args()
+
+    perturb_theta(args.ic_file, args.seed, args.magnitude)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/.github/actions/run-perturb-mpas/trim_history.py b/.github/actions/run-perturb-mpas/trim_history.py
new file mode 100644
index 0000000000..706b4268ef
--- /dev/null
+++ b/.github/actions/run-perturb-mpas/trim_history.py
@@ -0,0 +1,112 @@
+#!/usr/bin/env python3
+"""
+Trim MPAS history files for ECT ensemble processing.
+
+Extracts a single time slice, removes excluded variables, strips most
+static mesh geometry, and applies lossless NetCDF4 deflation (zlib).
+
+PyCECT requires three area-weighting variables (areaCell, dvEdge,
+areaTriangle) to compute global means. These static variables are
+preserved even though they lack a Time dimension.
+
+The ECT exclusion list path is configured via ECT_EXCLUDED_VARS in ci-config.env
+and passed via --exclude-file.
+
+Usage:
+    python3 trim_history.py input.nc output.nc --tslice -1 --exclude-file excluded_vars.txt
+"""
+
+import argparse
+import os
+import sys
+
+import netCDF4 as nc
+
+# Static variables PyCECT reads for area-weighted global means
+# (see pyEnsLib.py generate_global_mean_for_summary_MPAS, lines 745-758)
+PYCECT_REQUIRED_STATIC = {'areaCell', 'dvEdge', 'areaTriangle'}
+
+
+def trim_history(infile, outfile, tslice, exclude_vars=None):
+    exclude = set(exclude_vars or [])
+
+    with nc.Dataset(infile, 'r') as src, nc.Dataset(outfile, 'w', format='NETCDF4') as dst:
+        ntime = src.dimensions['Time'].size
+        if tslice < 0:
+            tslice = ntime + tslice
+        if tslice < 0 or tslice >= ntime:
+            print(f"ERROR: tslice={tslice} out of range for {ntime} time slice(s) in {infile}")
+            sys.exit(1)
+        dst.setncatts({k: src.getncattr(k) for k in src.ncattrs()})
+
+        # Copy ALL dimensions — PyCECT checks nCells/nEdges/nVertices
+        for dname, dim in src.dimensions.items():
+            if dname == 'Time':
+                dst.createDimension(dname, 1)
+            else:
+                dst.createDimension(dname, len(dim))
+
+        # Identify variables to keep:
+        #   1. Time-varying variables not in the exclude list
+        #   2. Static variables required by PyCECT for area weighting
+        keep_dynamic = {}
+        keep_static = {}
+        for name, var in src.variables.items():
+            if name in exclude:
+                continue
+            if 'Time' in var.dimensions:
+                keep_dynamic[name] = var
+            elif name in PYCECT_REQUIRED_STATIC:
+                keep_static[name] = var
+
+        kept = 0
+
+        # Write static variables (no time slicing needed)
+        for name, var in keep_static.items():
+            outvar = dst.createVariable(name, var.dtype, var.dimensions)
+            outvar.setncatts({k: var.getncattr(k) for k in var.ncattrs()})
+            outvar[:] = var[:]
+            kept += 1
+
+        # Write time-varying variables (extract single time slice, compress)
+        for name, var in keep_dynamic.items():
+            dims = var.dimensions
+            use_zlib = var.size > 1000
+            outvar = dst.createVariable(
+                name, var.dtype, dims,
+                zlib=use_zlib, complevel=1)
+            outvar.setncatts({k: var.getncattr(k) for k in var.ncattrs()})
+
+            tidx = dims.index('Time')
+            slices = [slice(None)] * len(dims)
+            slices[tidx] = slice(tslice, tslice + 1)
+            outvar[:] = var[tuple(slices)]
+            kept += 1
+
+        skipped = len(src.variables) - kept
+
+    in_size = os.path.getsize(infile) / 1048576
+    out_size = os.path.getsize(outfile) / 1048576
+    print(f"Kept {kept} variables ({len(keep_dynamic)} dynamic + "
+          f"{len(keep_static)} static), dropped {skipped}, "
+          f"tslice={tslice}, {in_size:.0f}MB -> {out_size:.0f}MB")
+
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser(
+        description='Trim MPAS history files for ECT')
+    parser.add_argument('input', help='Input history file')
+    parser.add_argument('output', help='Output trimmed file')
+    parser.add_argument('--tslice', type=int, default=-1,
+                        help='Time slice index to extract (negative counts from end, e.g. -1 = last)')
+    parser.add_argument('--exclude-file',
+                        help='File listing variable names to exclude')
+    args = parser.parse_args()
+
+    exclude = []
+    if args.exclude_file:
+        with open(args.exclude_file) as f:
+            exclude = [line.strip() for line in f
+                       if line.strip() and not line.startswith('#')]
+
+    trim_history(args.input, args.output, args.tslice, exclude)
diff --git a/.github/actions/validate-ect/action.yml b/.github/actions/validate-ect/action.yml
new file mode 100644
index 0000000000..c6037eaa89
--- /dev/null
+++ b/.github/actions/validate-ect/action.yml
@@ -0,0 +1,210 @@
+name: 'Validate ECT'
+description: >
+  Run PyCECT against an ensemble summary file to validate history output.
+  Installs PyCECT at the pinned version from ci-config.env, downloads the
+  ensemble summary from a GitHub release, runs pyCECT, and writes an
+  enriched result file with dimension metadata for the summary action.
+
+inputs:
+  history-dir:
+    description: 'Path to directory containing history .nc files to validate'
+    required: true
+  label:
+    description: 'Human-readable label for log annotations (e.g. gcc/mpich3/smiol/4proc)'
+    required: true
+  mpas-version:
+    description: 'MPAS version string (used to build the ect-v{version} release tag)'
+    required: true
+  dimensions:
+    description: 'Multi-line key=value pairs describing this test combination (written into result file)'
+    required: false
+    default: ''
+
+outputs:
+  result:
+    description: 'ECT result: PASSED, FAILED, SKIPPED, or ERROR'
+    value: ${{ steps.outcome.outputs.result }}
+  available:
+    description: 'Whether the ensemble summary file was found (true/false)'
+    value: ${{ steps.summary.outputs.available }}
+
+runs:
+  using: 'composite'
+  steps:
+    - name: Load ECT configuration
+      id: config
+      shell: bash
+      run: |
+        CI_CONFIG=".github/ci-config.env"
+        if [ ! -f "${CI_CONFIG}" ]; then
+          echo "::error::ci-config.env not found"
+          exit 1
+        fi
+        source "${CI_CONFIG}"
+
+        # ECT release tag is derived from the MPAS version (passed in),
+        # not stored in ci-config.env. See .github/actions/mpas-version.
+        echo "summary-file=${ECT_SUMMARY_FILE}" >> $GITHUB_OUTPUT
+        echo "pycect-tag=${PYCECT_TAG}" >> $GITHUB_OUTPUT
+        echo "pycect-commit=${PYCECT_COMMIT}" >> $GITHUB_OUTPUT
+        echo "release-tag=ect-v${{ inputs.mpas-version }}" >> $GITHUB_OUTPUT
+
+    - name: Install PyCECT dependencies
+      shell: bash
+      run: pip install "numpy<2" scipy netCDF4
+
+    - name: Clone PyCECT
+      shell: bash
+      run: |
+        TAG="${{ steps.config.outputs.pycect-tag }}"
+        COMMIT="${{ steps.config.outputs.pycect-commit }}"
+        echo "Cloning PyCECT at tag ${TAG} (commit ${COMMIT})..."
+        git clone --branch "${TAG}" https://github.com/NCAR/PyCECT.git pycect
+        cd pycect
+        if [ -n "${COMMIT}" ]; then
+          ACTUAL=$(git rev-parse HEAD)
+          if [ "${ACTUAL}" != "${COMMIT}" ]; then
+            echo "::error::PyCECT commit mismatch: expected ${COMMIT}, got ${ACTUAL}"
+            exit 1
+          fi
+        fi
+
+    - name: Download ensemble summary file
+      id: summary
+      shell: bash
+      run: |
+        source .github/ci-config.env
+        SUMMARY="${{ steps.config.outputs.summary-file }}"
+        TAG="${{ steps.config.outputs.release-tag }}"
+        REPO="${DATA_REPOSITORY:-${GITHUB_REPOSITORY}}"
+        URL="https://github.com/${REPO}/releases/download/${TAG}/${SUMMARY}"
+
+        echo "Downloading ${SUMMARY} from release ${TAG}..."
+        HTTP_CODE=$(curl --retry 5 --retry-delay 5 -sL -w "%{http_code}" \
+          "${URL}" -o "${SUMMARY}")
+        if [ "${HTTP_CODE}" != "200" ]; then
+          echo "::warning::Ensemble summary not available at ${URL} (HTTP ${HTTP_CODE})"
+          echo "available=false" >> $GITHUB_OUTPUT
+          exit 0
+        fi
+        echo "Downloaded summary file: $(du -h ${SUMMARY})"
+        echo "available=true" >> $GITHUB_OUTPUT
+        echo "summary-file=${SUMMARY}" >> $GITHUB_OUTPUT
+
+    - name: List test files
+      if: steps.summary.outputs.available == 'true'
+      shell: bash
+      run: |
+        echo "=== ECT test history files ==="
+        ls -la ${{ inputs.history-dir }}/ 2>/dev/null || echo "No history files found"
+
+    - name: Run PyCECT
+      id: pycect
+      if: steps.summary.outputs.available == 'true'
+      shell: bash
+      run: |
+        LABEL="${{ inputs.label }}"
+        # --tslice 0 is invariant: history files are pre-trimmed to a single
+        # time slice by run-perturb-mpas (trim_history.py creates Time=1).
+        set +e
+        python pycect/pyCECT.py \
+          --sumfile ${{ steps.summary.outputs.summary-file }} \
+          --indir ${{ inputs.history-dir }} \
+          --tslice 0 \
+          --mpas \
+          --verbose \
+          --printStdMean \
+          2>&1 | tee pycect_output.txt
+        PYCECT_STATUS=$?
+        set -e
+
+        if [ $PYCECT_STATUS -ne 0 ]; then
+          echo "::error::pyCECT crashed with exit code ${PYCECT_STATUS}"
+          echo "result=ERROR" >> $GITHUB_OUTPUT
+          exit 1
+        fi
+
+        if grep -qF '****PASSED****' pycect_output.txt; then
+          echo "::notice::ECT (${LABEL}): PASSED"
+          echo "result=PASSED" >> $GITHUB_OUTPUT
+        elif grep -qF '****FAILED****' pycect_output.txt; then
+          echo "::error::ECT (${LABEL}): FAILED"
+          echo "result=FAILED" >> $GITHUB_OUTPUT
+          exit 1
+        else
+          echo "::warning::Could not determine ECT result from pyCECT output"
+          echo "result=ERROR" >> $GITHUB_OUTPUT
+          exit 1
+        fi
+
+    - name: ECT Results
+      if: steps.pycect.outputs.result != ''
+      shell: bash
+      run: |
+        LABEL="${{ inputs.label }}"
+        RESULT="${{ steps.pycect.outputs.result }}"
+
+        if [ "${RESULT}" = "PASSED" ]; then
+          ICON=":white_check_mark:"
+        else
+          ICON=":x:"
+        fi
+
+        {
+          echo "## ECT Result: ${ICON} ${RESULT}"
+          echo ""
+          echo "**Configuration:** \`${LABEL}\`"
+          echo ""
+          echo '```'
+          grep -E '(PASSED|FAILED|global|regional|Overall)' pycect_output.txt || true
+          echo '```'
+          if grep -q 'standardized mean' pycect_output.txt; then
+            echo ""
+            echo "<details><summary>Standardized Mean Summary</summary>"
+            echo ""
+            echo '```'
+            grep 'standardized mean' pycect_output.txt || true
+            echo '```'
+            echo "</details>"
+          fi
+        } >> "$GITHUB_STEP_SUMMARY"
+
+        echo "================================"
+        echo "  ECT Result: ${RESULT}"
+        echo "  Label:      ${LABEL}"
+        echo "================================"
+
+    - name: Fail if summary unavailable
+      if: steps.summary.outputs.available != 'true'
+      shell: bash
+      run: |
+        {
+          echo "## ECT Result: :warning: SKIPPED"
+          echo ""
+          echo "Ensemble summary file not found. Run \`ect-ensemble-gen.yml\` first."
+        } >> "$GITHUB_STEP_SUMMARY"
+        echo "::error::ECT validation cannot run — ensemble summary file not found. Run ect-ensemble-gen.yml first."
+        exit 1
+
+    - name: Write result file
+      id: outcome
+      if: always()
+      shell: bash
+      run: |
+        RESULT="${{ steps.pycect.outputs.result }}"
+        if [ -z "${RESULT}" ]; then
+          if [ "${{ steps.summary.outputs.available }}" != "true" ]; then
+            RESULT="SKIPPED"
+          else
+            RESULT="NO_DATA"
+          fi
+        fi
+        echo "result=${RESULT}" >> $GITHUB_OUTPUT
+
+        {
+          echo "result=${RESULT}"
+          DIMS="${{ inputs.dimensions }}"
+          if [ -n "${DIMS}" ]; then
+            echo "${DIMS}"
+          fi
+        } > ect-result.txt
diff --git a/.github/ci-config.env b/.github/ci-config.env
new file mode 100644
index 0000000000..7d50cad77c
--- /dev/null
+++ b/.github/ci-config.env
@@ -0,0 +1,75 @@
+# .github/ci-config.env — Central CI configuration
+#
+# Sourced by workflows and composite actions. Edit here to change
+# containers, compilers, test data versions, or ECT parameters.
+
+
+# ── Container images ──────────────────────────────
+# {compiler} and {mpi} are replaced by resolve-container.
+# Tags: https://hub.docker.com/r/ncarcisl/hpcdev-x86_64/tags
+
+CONTAINER_IMAGE="docker.io/ncarcisl/hpcdev-x86_64:almalinux9-{compiler}-{mpi}-26.02"
+
+# Per-compiler override: CONTAINER_IMAGE_{compiler}="template"
+
+
+# ── Container name mappings ───────────────────────
+# Map CI compiler/MPI names to Docker Hub tag strings when they differ.
+
+CONTAINER_COMPILER_gcc=gcc14
+# CONTAINER_MPI_mpich=mpich3
+
+
+# ── Makefile target mapping ───────────────────────
+# MAKE_TARGET_{compiler} → MPAS Makefile target name.
+
+MAKE_TARGET_gcc=gfortran
+MAKE_TARGET_nvhpc=nvhpc
+MAKE_TARGET_oneapi=intel
+MAKE_TARGET_clang=llvm
+
+
+# ── Compiler workarounds ─────────────────────────
+
+# Portable target arch (CI builds and runs on different hosts).
+NVHPC_TARGET_ARCH=-tp=px
+
+# Disable MPI Fortran 2008 bindings (not supported by MPICH
+# builds in current containers).
+NVHPC_EXTRA_MAKE_FLAGS="MPAS_MPI_F08=0"
+ONEAPI_EXTRA_MAKE_FLAGS="MPAS_MPI_F08=0"
+
+
+# ── MPI runtime flags ────────────────────────────
+# Needed because CI runs inside containers as root.
+# Used in actions/run-mpas and actions/run-perturb-mpas.
+
+OPENMPI_RUN_FLAGS="--allow-run-as-root --oversubscribe"
+
+
+# ── Test data ─────────────────────────────────────
+# Test data and ECT summaries are hosted as GitHub release assets
+# on NCAR/MPAS-Model-CI. Workflows use this variable to resolve
+# download URLs.
+
+DATA_REPOSITORY=NCAR/MPAS-Model-CI
+
+RELEASE_TESTDATA_240KM=testdata-240km-v3
+RELEASE_TESTDATA_120KM=testdata-120km-v2
+
+
+# ── ECT configuration ────────────────────────────
+# Ensemble Consistency Test (PyCECT) parameters.
+# The ECT release tag (ect-v{MPAS_VERSION}) is derived at runtime
+# from src/core_atmosphere/Registry.xml by the mpas-version action.
+
+ECT_RESOLUTION=120km
+ECT_ENSEMBLE_SIZE=200
+ECT_PERTURB_MAGNITUDE=1e-14
+ECT_PERTURB_VARIABLE=theta
+ECT_SUMMARY_FILE=mpas_ect_summary_120km.nc
+ECT_RESTART_FILE=120km-spinup-restart.nc
+ECT_EXCLUDED_VARS=.github/data/ect_excluded_vars.txt
+PYCECT_TAG=3.3.1
+PYCECT_COMMIT=b3c36a9d72ee211f396d1bc7078f6d5466916b0a
+
diff --git a/.github/data/ect_excluded_vars.txt b/.github/data/ect_excluded_vars.txt
new file mode 100644
index 0000000000..478c6e786a
--- /dev/null
+++ b/.github/data/ect_excluded_vars.txt
@@ -0,0 +1,35 @@
+# Variables excluded from ECT history files to reduce artifact size.
+# These are either not analyzed by PyCECT or are expensive research
+# diagnostics not needed for consistency testing.
+#
+# Ertel PV diagnostics (3D cell fields, ~12MB each on 120km mesh)
+ertel_pv
+u_pv
+v_pv
+theta_pv
+vort_pv
+iLev_DT
+#
+# PV tendency terms (3D cell fields, only present with physics enabled)
+depv_dt_lw
+depv_dt_sw
+depv_dt_bl
+depv_dt_cu
+depv_dt_mix
+dtheta_dt_mp
+depv_dt_mp
+depv_dt_diab
+depv_dt_fric
+depv_dt_diab_pv
+depv_dt_fric_pv
+#
+# Edge velocity — PyCECT recommends uReconstructZonal/Meridional instead
+u
+#
+# Integer variables — PyCECT excludes these automatically
+i_rainnc
+i_rainc
+kpbl
+#
+# Time metadata string
+xtime
diff --git a/.github/workflows/_test-compiler.yml b/.github/workflows/_test-compiler.yml
new file mode 100644
index 0000000000..bd132eb139
--- /dev/null
+++ b/.github/workflows/_test-compiler.yml
@@ -0,0 +1,258 @@
+# Reusable workflow: build and validate MPAS-A for a single compiler+MPI using ECT.
+# Called by per-compiler per-MPI subset workflows (e.g. test-gcc-mpich.yml).
+#
+# Runs ECT with 4 MPI ranks. Validation uses the Ensemble Consistency Test
+# (PyCECT) — perturbed runs compared against a pre-built ensemble summary —
+# instead of bit-for-bit log comparison.
+
+name: _test-compiler
+
+permissions:
+  contents: read
+
+on:
+  workflow_call:
+    inputs:
+      compiler:
+        description: 'Compiler family (gcc, nvhpc, oneapi)'
+        required: true
+        type: string
+      mpi:
+        description: 'MPI implementation (mpich, openmpi)'
+        required: true
+        type: string
+      mpas-repository:
+        description: 'MPAS source repo (e.g. MPAS-Dev/MPAS-Model). Empty = this repo.'
+        required: false
+        type: string
+        default: ''
+      mpas-ref:
+        description: 'Git ref in the MPAS source repo (branch, tag, SHA)'
+        required: false
+        type: string
+        default: ''
+
+jobs:
+  config:
+    name: Resolve Config
+    runs-on: ubuntu-latest
+    outputs:
+      image: ${{ steps.container.outputs.image }}
+      mpas-version: ${{ steps.version.outputs.version }}
+    steps:
+      - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
+        with:
+          sparse-checkout: |
+            .github
+            src/core_atmosphere/Registry.xml
+          sparse-checkout-cone-mode: false
+          persist-credentials: false
+      - uses: ./.github/actions/resolve-container
+        id: container
+        with:
+          compiler: ${{ inputs.compiler }}
+          mpi: ${{ inputs.mpi }}
+      - uses: ./.github/actions/mpas-version
+        id: version
+
+  build:
+    needs: config
+    name: Build (${{ inputs.compiler }}, ${{ inputs.mpi }}, smiol)
+    runs-on: ubuntu-latest
+    container:
+      image: ${{ needs.config.outputs.image }}
+
+    steps:
+      - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
+        with:
+          repository: ${{ inputs.mpas-repository || github.repository }}
+          ref: ${{ inputs.mpas-ref || '' }}
+          submodules: 'true'
+          persist-credentials: false
+
+      - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
+        if: ${{ inputs.mpas-repository != '' }}
+        with:
+          path: _ci
+          sparse-checkout: .github
+          persist-credentials: false
+
+      - name: Overlay CI infrastructure
+        if: ${{ inputs.mpas-repository != '' }}
+        shell: bash
+        run: |
+          cp -r _ci/.github . && rm -rf _ci
+          echo "## Source: ${{ inputs.mpas-repository }}@${{ inputs.mpas-ref }}" >> "$GITHUB_STEP_SUMMARY"
+
+      - name: Build MPAS-A (double precision)
+        uses: ./.github/actions/build-mpas
+        with:
+          compiler: ${{ inputs.compiler }}
+          use-pio: 'false'
+          precision: double
+
+      - name: Upload executable
+        uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6
+        with:
+          name: exe-${{ inputs.compiler }}-${{ inputs.mpi }}-smiol
+          path: atmosphere_model
+          retention-days: 1
+
+  ect-run:
+    needs: [config, build]
+    if: ${{ needs.build.result == 'success' }}
+    strategy:
+      fail-fast: false
+      matrix:
+        member: [0, 1, 2]
+
+    name: ECT member ${{ matrix.member }} (${{ inputs.compiler }}, ${{ inputs.mpi }})
+    runs-on: ubuntu-latest
+    container:
+      image: ${{ needs.config.outputs.image }}
+
+    steps:
+      - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
+        with:
+          persist-credentials: false
+
+      - name: Download executable
+        id: download
+        uses: actions/download-artifact@37930b1c2abaa49bbe596cd826c3c89aef350131 # v7
+        continue-on-error: true
+        with:
+          name: exe-${{ inputs.compiler }}-${{ inputs.mpi }}-smiol
+
+      - name: Download test case
+        if: steps.download.outcome == 'success'
+        uses: ./.github/actions/download-testdata
+        with:
+          resolution: 120km
+          dest-dir: base-case
+
+      - name: Restore cached restart
+        if: steps.download.outcome == 'success'
+        id: cache-restart
+        uses: actions/cache/restore@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5
+        with:
+          path: spinup-restart.nc
+          key: ect-spinup-restart-${{ hashFiles('.github/ci-config.env') }}
+
+      - name: Download spin-up restart
+        if: steps.download.outcome == 'success'
+        id: restart
+        shell: bash
+        run: |
+          source .github/ci-config.env
+          RESTART="${ECT_RESTART_FILE}"
+          RELEASE_TAG="ect-v${{ needs.config.outputs.mpas-version }}"
+
+          if [ -f "spinup-restart.nc" ]; then
+            echo "Using cached restart file"
+            mv spinup-restart.nc "${RESTART}"
+            echo "available=true" >> $GITHUB_OUTPUT
+            echo "file=${RESTART}" >> $GITHUB_OUTPUT
+            exit 0
+          fi
+
+          DATA_REPO="${DATA_REPOSITORY:-${GITHUB_REPOSITORY}}"
+          echo "Downloading ${RESTART}.gz from ${DATA_REPO} release ${RELEASE_TAG}..."
+          HTTP_CODE=$(curl -sL --retry 5 --retry-delay 5 -w "%{http_code}" \
+            "https://github.com/${DATA_REPO}/releases/download/${RELEASE_TAG}/${RESTART}.gz" \
+            -o "${RESTART}.gz")
+          if [ "${HTTP_CODE}" = "200" ]; then
+            gunzip "${RESTART}.gz"
+            echo "Downloaded restart: $(du -h ${RESTART})"
+            echo "available=true" >> $GITHUB_OUTPUT
+            echo "file=${RESTART}" >> $GITHUB_OUTPUT
+          else
+            echo "::warning::Spin-up restart not available (HTTP ${HTTP_CODE}), running from cold-start init.nc"
+            echo "available=false" >> $GITHUB_OUTPUT
+          fi
+
+      - name: Run perturbed MPAS-A (member ${{ matrix.member }})
+        if: steps.download.outcome == 'success'
+        uses: ./.github/actions/run-perturb-mpas
+        with:
+          base-dir: base-case
+          executable: ./atmosphere_model
+          member-start: '${{ matrix.member }}'
+          member-end: '${{ matrix.member }}'
+          num-ranks: '4'
+          mpi-impl: ${{ inputs.mpi }}
+          run-duration: '0_02:36:00'
+          run-timeout: '45'
+          restart-file: ${{ steps.restart.outputs.available == 'true' && steps.restart.outputs.file || '' }}
+
+      - name: Upload history file
+        uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6
+        if: always() && steps.download.outcome == 'success'
+        with:
+          name: ect-history-${{ inputs.compiler }}-${{ inputs.mpi }}-member${{ matrix.member }}
+          path: history-output/history.*.nc
+          retention-days: 1
+
+  ect-validate:
+    needs: [config, ect-run]
+    if: ${{ needs.ect-run.result == 'success' }}
+    name: ECT Validate (${{ inputs.compiler }}, ${{ inputs.mpi }})
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
+        with:
+          sparse-checkout: .github
+          persist-credentials: false
+
+      - uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6
+        with:
+          python-version: '3.11'
+
+      - name: Download history files
+        id: download
+        continue-on-error: true
+        uses: actions/download-artifact@37930b1c2abaa49bbe596cd826c3c89aef350131 # v7
+        with:
+          pattern: ect-history-${{ inputs.compiler }}-${{ inputs.mpi }}-*
+          path: ect-test-files
+          merge-multiple: true
+
+      - name: Run ECT validation
+        if: steps.download.outcome == 'success'
+        uses: ./.github/actions/validate-ect
+        with:
+          history-dir: ect-test-files
+          label: ${{ inputs.compiler }}/${{ inputs.mpi }}/smiol
+          mpas-version: ${{ needs.config.outputs.mpas-version }}
+          dimensions: |
+            compiler=${{ inputs.compiler }}
+            mpi=${{ inputs.mpi }}
+            io=smiol
+
+      - name: Upload result
+        if: always()
+        uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6
+        with:
+          name: ect-result-${{ inputs.compiler }}-${{ inputs.mpi }}
+          path: ect-result.txt
+          retention-days: 1
+
+  cleanup:
+    needs: [ect-run, ect-validate]
+    if: always()
+    runs-on: ubuntu-latest
+    name: Cleanup
+    permissions:
+      actions: write
+
+    steps:
+      - name: Delete temporary artifacts
+        env:
+          GH_TOKEN: ${{ github.token }}
+        shell: bash
+        run: |
+          gh api repos/${{ github.repository }}/actions/runs/${{ github.run_id }}/artifacts \
+            --paginate --jq '.artifacts[] | select(.name | startswith("exe-") or startswith("ect-history-")) | .id' \
+          | while read id; do
+              gh api -X DELETE repos/${{ github.repository }}/actions/artifacts/$id || true
+            done || true
diff --git a/.github/workflows/test-gcc-mpich.yml b/.github/workflows/test-gcc-mpich.yml
new file mode 100644
index 0000000000..92085b509e
--- /dev/null
+++ b/.github/workflows/test-gcc-mpich.yml
@@ -0,0 +1,19 @@
+# Subset CI: GNU + MPICH (CPU)
+# Quick ECT validation with 4 MPI ranks.
+
+name: "GNU+MPICH (CPU)"
+
+on:
+  workflow_dispatch:
+  push:
+    branches: [master, develop, 'feature/ci-cpu-testing']
+  pull_request:
+    branches: [master, develop, 'feature/ci-cpu-testing']
+
+jobs:
+  test:
+    uses: ./.github/workflows/_test-compiler.yml
+    with:
+      compiler: gcc
+      mpi: mpich
+
diff --git a/.github/workflows/test-gcc-openmpi.yml b/.github/workflows/test-gcc-openmpi.yml
new file mode 100644
index 0000000000..c8d2749e20
--- /dev/null
+++ b/.github/workflows/test-gcc-openmpi.yml
@@ -0,0 +1,19 @@
+# Subset CI: GNU + OpenMPI (CPU)
+# Quick ECT validation with 4 MPI ranks.
+
+name: "GNU+OpenMPI (CPU)"
+
+on:
+  workflow_dispatch:
+  push:
+    branches: [master, develop, 'feature/ci-cpu-testing']
+  pull_request:
+    branches: [master, develop, 'feature/ci-cpu-testing']
+
+jobs:
+  test:
+    uses: ./.github/workflows/_test-compiler.yml
+    with:
+      compiler: gcc
+      mpi: openmpi
+
diff --git a/.github/workflows/test-intel-mpich.yml b/.github/workflows/test-intel-mpich.yml
new file mode 100644
index 0000000000..d7f0ab62d7
--- /dev/null
+++ b/.github/workflows/test-intel-mpich.yml
@@ -0,0 +1,19 @@
+# Subset CI: Intel + MPICH (CPU)
+# Quick ECT validation with 4 MPI ranks.
+
+name: "Intel+MPICH (CPU)"
+
+on:
+  workflow_dispatch:
+  push:
+    branches: [master, develop, 'feature/ci-cpu-testing']
+  pull_request:
+    branches: [master, develop, 'feature/ci-cpu-testing']
+
+jobs:
+  test:
+    uses: ./.github/workflows/_test-compiler.yml
+    with:
+      compiler: oneapi
+      mpi: mpich
+
diff --git a/.github/workflows/test-intel-openmpi.yml b/.github/workflows/test-intel-openmpi.yml
new file mode 100644
index 0000000000..40f1a010ae
--- /dev/null
+++ b/.github/workflows/test-intel-openmpi.yml
@@ -0,0 +1,19 @@
+# Subset CI: Intel + OpenMPI (CPU)
+# Quick ECT validation with 4 MPI ranks.
+
+name: "Intel+OpenMPI (CPU)"
+
+on:
+  workflow_dispatch:
+  push:
+    branches: [master, develop, 'feature/ci-cpu-testing']
+  pull_request:
+    branches: [master, develop, 'feature/ci-cpu-testing']
+
+jobs:
+  test:
+    uses: ./.github/workflows/_test-compiler.yml
+    with:
+      compiler: oneapi
+      mpi: openmpi
+
diff --git a/.github/workflows/test-nvhpc-mpich.yml b/.github/workflows/test-nvhpc-mpich.yml
new file mode 100644
index 0000000000..14e66fbf34
--- /dev/null
+++ b/.github/workflows/test-nvhpc-mpich.yml
@@ -0,0 +1,19 @@
+# Subset CI: NVHPC + MPICH (CPU)
+# Quick ECT validation with 4 MPI ranks.
+
+name: "NVHPC+MPICH (CPU)"
+
+on:
+  workflow_dispatch:
+  push:
+    branches: [master, develop, 'feature/ci-cpu-testing']
+  pull_request:
+    branches: [master, develop, 'feature/ci-cpu-testing']
+
+jobs:
+  test:
+    uses: ./.github/workflows/_test-compiler.yml
+    with:
+      compiler: nvhpc
+      mpi: mpich
+
diff --git a/.github/workflows/test-nvhpc-openmpi.yml b/.github/workflows/test-nvhpc-openmpi.yml
new file mode 100644
index 0000000000..094628d1ae
--- /dev/null
+++ b/.github/workflows/test-nvhpc-openmpi.yml
@@ -0,0 +1,21 @@
+# Subset CI: NVHPC + OpenMPI (CPU)
+# Quick ECT validation with 4 MPI ranks.
+# Known issue: model exits 134 (SIGABRT) on GA runners with 4 ranks.
+# MPICH works.
+
+name: "NVHPC+OpenMPI (CPU)"
+
+on:
+  workflow_dispatch:
+  push:
+    branches: [master, develop, 'feature/ci-cpu-testing']
+  pull_request:
+    branches: [master, develop, 'feature/ci-cpu-testing']
+
+jobs:
+  test:
+    uses: ./.github/workflows/_test-compiler.yml
+    with:
+      compiler: nvhpc
+      mpi: openmpi
+
diff --git a/README.md b/README.md
index 8db0d85898..73d7043712 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,25 @@
 MPAS-v8.4.0
 ====
 
+## CI Status
+
+Each test builds MPAS-Atmosphere in double precision, runs 3 perturbed ensemble
+members (4 MPI ranks), and validates with
+[PyCECT](https://github.com/NCAR/PyCECT)
+([Price-Broncucia et al. 2025](https://doi.org/10.5194/gmd-18-2349-2025)).
+All testing subsets run automatically on every push and PR to the
+master and develop branches. Reminder: Feature PRs should be opened
+against `develop`.
+
+| Compiler | MPI | Status |
+|----------|-----|--------|
+| GNU | MPICH | [![GNU+MPICH (CPU)](https://github.com/MPAS-Dev/MPAS-Model/actions/workflows/test-gcc-mpich.yml/badge.svg)](https://github.com/MPAS-Dev/MPAS-Model/actions/workflows/test-gcc-mpich.yml) |
+| GNU | OpenMPI | [![GNU+OpenMPI (CPU)](https://github.com/MPAS-Dev/MPAS-Model/actions/workflows/test-gcc-openmpi.yml/badge.svg)](https://github.com/MPAS-Dev/MPAS-Model/actions/workflows/test-gcc-openmpi.yml) |
+| Intel | MPICH | [![Intel+MPICH (CPU)](https://github.com/MPAS-Dev/MPAS-Model/actions/workflows/test-intel-mpich.yml/badge.svg)](https://github.com/MPAS-Dev/MPAS-Model/actions/workflows/test-intel-mpich.yml) |
+| Intel | OpenMPI | [![Intel+OpenMPI (CPU)](https://github.com/MPAS-Dev/MPAS-Model/actions/workflows/test-intel-openmpi.yml/badge.svg)](https://github.com/MPAS-Dev/MPAS-Model/actions/workflows/test-intel-openmpi.yml) |
+| NVHPC | MPICH | [![NVHPC+MPICH (CPU)](https://github.com/MPAS-Dev/MPAS-Model/actions/workflows/test-nvhpc-mpich.yml/badge.svg)](https://github.com/MPAS-Dev/MPAS-Model/actions/workflows/test-nvhpc-mpich.yml) |
+| NVHPC | OpenMPI | [![NVHPC+OpenMPI (CPU)](https://github.com/MPAS-Dev/MPAS-Model/actions/workflows/test-nvhpc-openmpi.yml/badge.svg)](https://github.com/MPAS-Dev/MPAS-Model/actions/workflows/test-nvhpc-openmpi.yml) |
+
 The Model for Prediction Across Scales (MPAS) is a collaborative project for
 developing atmosphere, ocean, and other earth-system simulation components for
 use in climate, regional climate, and weather studies. The primary development