diff --git a/.github/workflows/test-linux.yaml b/.github/workflows/test-linux.yaml
index 264aeea..418ff49 100644
--- a/.github/workflows/test-linux.yaml
+++ b/.github/workflows/test-linux.yaml
@@ -27,15 +27,6 @@ jobs:
         restore-keys: |
              ${{ runner.os }}-stack-global
 
-    - name: 💾 Restore cached stack-installed programs in ~/.local/bin
-      id:   stack-programs
-      uses: actions/cache/restore@v3
-      with:
-        path: ~/.local/bin
-        key: ${{ runner.os }}-stack-programs-${{ hashFiles('**.yaml') }}
-        restore-keys: |
-             ${{ runner.os }}-stack-programs
-
     - name: 💾 Restore cached .stack-work
       id:   stack-work
       uses: actions/cache/restore@v3
@@ -49,10 +40,11 @@ jobs:
 
     - name: ⏬ Install stack
       run: |
-        mkdir -p ~/.local/bin
-        export PATH=~/.local/bin:$PATH
+        # mkdir -p ~/.local/bin
+        # export PATH=~/.local/bin:$PATH
+        ## Stack is preinstalled on the GHA runners
         # curl -sL https://get.haskellstack.org/stable/linux-x86_64.tar.gz | tar xz --wildcards --strip-components=1 -C ~/.local/bin '*/stack'; chmod a+x ~/.local/bin/stack
-        if [[ ! -x ~/.local/bin/stack ]]; then curl -sL https://get.haskellstack.org/stable/linux-x86_64.tar.gz | tar xz --wildcards --strip-components=1 -C ~/.local/bin '*/stack'; chmod a+x ~/.local/bin/stack; fi
+        # if [[ ! -x ~/.local/bin/stack ]]; then curl -sL https://get.haskellstack.org/stable/linux-x86_64.tar.gz | tar xz --wildcards --strip-components=1 -C ~/.local/bin '*/stack'; chmod a+x ~/.local/bin/stack; fi
         stack --version
 
     - name: ⏬ Install GHC
@@ -78,13 +70,6 @@ jobs:
         path: ~/.stack
         key: ${{ steps.stack-global.outputs.cache-primary-key }}
 
-    - name: 💾 Cache stack-installed programs in ~/.local/bin
-      if:   always() && steps.stack-programs.outputs.cache-hit != 'true'
-      uses: actions/cache/save@v3
-      with:
-        path: ~/.local/bin
-        key: ${{ steps.stack-programs.outputs.cache-primary-key }}
-
     - name: 💾 Cache .stack-work
       if:   always() && steps.stack-work.outputs.cache-hit != 'true'
       uses: actions/cache/save@v3
diff --git a/.github/workflows/test-mac.yaml b/.github/workflows/test-mac.yaml
index 1cf9120..7098188 100644
--- a/.github/workflows/test-mac.yaml
+++ b/.github/workflows/test-mac.yaml
@@ -27,15 +27,6 @@ jobs:
         restore-keys: |
              ${{ runner.os }}-stack-global
 
-    - name: 💾 Restore cached stack-installed programs in ~/.local/bin
-      id:   stack-programs
-      uses: actions/cache/restore@v3
-      with:
-        path: ~/.local/bin
-        key: ${{ runner.os }}-stack-programs-${{ hashFiles('**.yaml') }}
-        restore-keys: |
-             ${{ runner.os }}-stack-programs
-
     - name: 💾 Restore cached .stack-work
       id:   stack-work
       uses: actions/cache/restore@v3
@@ -53,10 +44,11 @@ jobs:
 
     - name: ⏬ Install stack
       run: |
-        mkdir -p ~/.local/bin
-        export PATH=~/.local/bin:$PATH
+        # mkdir -p ~/.local/bin
+        # export PATH=~/.local/bin:$PATH
+        ## Stack is preinstalled on the GHA runners
         # brew install gnu-tar; curl -sL https://get.haskellstack.org/stable/osx-x86_64.tar.gz | gtar xz --wildcards --strip-components=1 -C ~/.local/bin '*/stack'; chmod a+x ~/.local/bin/stack
-        if [[ ! -x ~/.local/bin/stack ]]; then brew install gnu-tar; curl -sL https://get.haskellstack.org/stable/osx-x86_64.tar.gz | gtar xz --wildcards --strip-components=1 -C ~/.local/bin '*/stack'; chmod a+x ~/.local/bin/stack; fi
+        # if [[ ! -x ~/.local/bin/stack ]]; then brew install gnu-tar; curl -sL https://get.haskellstack.org/stable/osx-x86_64.tar.gz | gtar xz --wildcards --strip-components=1 -C ~/.local/bin '*/stack'; chmod a+x ~/.local/bin/stack; fi
         stack --version
 
     - name: ⏬ Install GHC
@@ -80,13 +72,6 @@ jobs:
         path: ~/.stack
         key: ${{ steps.stack-global.outputs.cache-primary-key }}
 
-    - name: 💾 Cache stack-installed programs in ~/.local/bin
-      if:   always() && steps.stack-programs.outputs.cache-hit != 'true'
-      uses: actions/cache/save@v3
-      with:
-        path: ~/.local/bin
-        key: ${{ steps.stack-programs.outputs.cache-primary-key }}
-
     - name: 💾 Cache .stack-work
       if:   always() && steps.stack-work.outputs.cache-hit != 'true'
       uses: actions/cache/save@v3
diff --git a/.github/workflows/test-windows.yaml b/.github/workflows/test-windows.yaml
index e02dbbb..3a25690 100644
--- a/.github/workflows/test-windows.yaml
+++ b/.github/workflows/test-windows.yaml
@@ -8,11 +8,21 @@ on:
   pull_request:
     branches: [master]
 
+defaults:
+  run:
+    shell: bash
+
 jobs:
   build:
     runs-on: windows-latest
     steps:
 
+    - name: Determine stack root
+      run: |
+        STACK_ROOT="$(stack --system-ghc --no-install-ghc path --stack-root)"
+        echo "STACK_ROOT = ${STACK_ROOT}"
+        echo STACK_ROOT="${STACK_ROOT:-C:/Users/runneradmin/AppData/Local/Programs/stack/x86_64-windows}" >> "${GITHUB_ENV}"
+
     - name: 📥 Checkout repository
       uses: actions/checkout@v4
 
@@ -22,21 +32,10 @@ jobs:
       id:   stack-global
       uses: actions/cache/restore@v3
       with:
-        path: C:\Users\runneradmin\AppData\Roaming\stack\
-        key: ${{ runner.os }}-appdata-roaming-stack-${{ hashFiles('**.yaml') }}
-        restore-keys: |
-             ${{ runner.os }}-appdata-roaming-stack
-
-    - name: 💾 Restore cached stack-installed programs in ~/.local/bin
-      id:   stack-programs
-      uses: actions/cache/restore@v3
-      with:
-        path: C:\Users\runneradmin\AppData\Local\Programs\stack\
-        # which files signal a change in stack's global db ?
-        # **.yaml includes */package.yaml and stack.yaml* (too many), and hopefully no other changing yamls
-        key: ${{ runner.os }}-appdata-local-programs-stack-${{ hashFiles('**.yaml') }}
+        path: ${{ env.STACK_ROOT }}
+        key: ${{ runner.os }}-stack-global-${{ hashFiles('**.yaml') }}
         restore-keys: |
-             ${{ runner.os }}-appdata-local-programs-stack
+             ${{ runner.os }}-stack-global
 
     - name: 💾 Restore cached .stack-work
       id:   stack-work
@@ -50,39 +49,37 @@ jobs:
     # actions
 
     - name: ⏬ Install stack
+      ## Stack is preinstalled on GHA runners.
+      #
       #if: steps.stack-programs-dir.outputs.cache-hit != 'true'
       # this step is needed to get stack.exe into PATH, for now
+        # curl -sL https://get.haskellstack.org/stable/windows-x86_64.zip -o stack.zip
+        # 7z x stack.zip stack.exe
       run: |
-        curl -sL https://get.haskellstack.org/stable/windows-x86_64.zip -o stack.zip
-        7z x stack.zip stack.exe
         which stack
         stack --version
-        which ./stack
-        ./stack --version
-      # must avoid GHC versions broken on windows such as 8.8.3 with https://gitlab.haskell.org/ghc/ghc/issues/17926
-      # current default stack.yaml uses GHC 8.8.4 which hopefully is ok
 
     - name: ⏬ Install GHC
       # if: steps.stack-programs-dir.outputs.cache-hit != 'true'
       # set PATH=C:\Users\runneradmin\AppData\Local\Programs\stack\local\bin;%PATH%
       run: |
-        ./stack --no-terminal setup --install-ghc
+        stack --no-terminal setup --install-ghc
 
     - name: Install the icu library
       run: |
-        ./stack exec -- pacman -S --noconfirm mingw-w64-x86_64-icu mingw-w64-x86_64-pkgconf
+        stack exec -- pacman -S --noconfirm mingw-w64-x86_64-icu mingw-w64-x86_64-pkgconf
 
     - name: 📸 Build Snapshot
       run: |
-        ./stack build --no-terminal --only-snapshot -j1
+        stack build --no-terminal --only-snapshot -j1
 
     - name: 🧰 Build Dependencies
       run: |
-        ./stack build --no-terminal --only-dependencies
+        stack build --no-terminal --only-dependencies
 
     - name: 🔨 Build and run tests
       run: |
-        ./stack test
+        stack test
 
     # things to be cached
 
@@ -90,16 +87,9 @@ jobs:
       if:   always() && steps.stack-global.outputs.cache-hit != 'true'
       uses: actions/cache/save@v3
       with:
-        path: ~/.stack
+        path: ${{ env.STACK_ROOT }}
         key: ${{ steps.stack-global.outputs.cache-primary-key }}
 
-    - name: 💾 Cache stack-installed programs in ~/.local/bin
-      if:   always() && steps.stack-programs.outputs.cache-hit != 'true'
-      uses: actions/cache/save@v3
-      with:
-        path: ~/.local/bin
-        key: ${{ steps.stack-programs.outputs.cache-primary-key }}
-
     - name: 💾 Cache .stack-work
       if:   always() && steps.stack-work.outputs.cache-hit != 'true'
       uses: actions/cache/save@v3