ci(windows): replace S3 MSYS2 zip with cached pacman install of clang 18.1.8

.github/actions/install-msys2-mrbind/action.yml

@@ -1,27 +1,25 @@
-name: 'Install MSYS2 for MRBind'
-description: 'Download the MeshLib MSYS2 archive from S3 with retry on transient failures and extract to C:\'
+name: Install MSYS2 for MRBind
+description: >
+  Restore (or download) the clang-18 MSYS2 toolchain pinned by
+  `scripts/mrbind/msys2_package_hashes_clang18.txt`, sha256-verify
+  it, and `pacman -U` against the runner's preinstalled `C:\msys64`.
+
 runs:
-  using: 'composite'
+  using: composite
   steps:
+    - name: Cache pinned MSYS2 packages
+      # Cache key tracks the lockfile; `wget -nc` makes cache-hit a no-op,
+      # and `sha256sum -c` in the install script is the integrity gate.
+      uses: actions/cache@v5
+      with:
+        path: scripts/mrbind/msys2_packages
+        key: msys2-mrbind-clang18-${{ hashFiles('scripts/mrbind/msys2_package_hashes_clang18.txt') }}
+
     - name: Install MSYS2 for MRBind
+      # Pin clang to 18.1.8 — same version master's S3 zip ships.
+      # Pinning only clang/llvm causes `STATUS_DLL_NOT_FOUND` from
+      # cc.exe, so the lockfile carries the whole clang-18-era
+      # runtime stack.
       shell: pwsh
       run: |
-        # Retry the S3 fetch -- transient 404 / connection blips have been
-        # observed against vcpkg-export.s3.us-east-1.amazonaws.com.
-        $url = "https://vcpkg-export.s3.us-east-1.amazonaws.com/msys64_meshlib_mrbind.zip"
-        $dest = "./msys64_meshlib_mrbind.zip"
-        $maxAttempts = 5
-        $delay = 10
-        for ($i = 1; $i -le $maxAttempts; $i++) {
-          try {
-            (New-Object Net.WebClient).DownloadFile($url, $dest)
-            break
-          } catch {
-            if ($i -eq $maxAttempts) { throw }
-            Write-Host "Download attempt $i failed: $($_.Exception.Message). Retrying in $delay s..."
-            Start-Sleep -Seconds $delay
-            $delay *= 2
-          }
-        }
-        [IO.Compression.ZipFile]::ExtractToDirectory($dest, "C:\")
-        rm $dest
+        C:\msys64\msys2_shell.cmd -no-start -defterm -here -c "set -e && bash scripts/mrbind/msys2_download_packages.sh _clang18 && bash scripts/mrbind/msys2_install_packages.sh _clang18"

.github/workflows/build-test-windows.yml

@@ -142,19 +142,18 @@ jobs:
         if: ${{inputs.mrbind || (inputs.mrbind_c && matrix.build_system == 'CMake') || env.BUILD_C_SHARP == 'true'}}
         uses: ./.github/actions/install-msys2-mrbind
 
-      - name: Install gettext utilities
-        if: ${{ inputs.upload_artifacts }}
-        run: |
-          C:\msys64_meshlib_mrbind\msys2_shell.cmd -clang64 -defterm -no-start -c "pacman -S --noconfirm --needed mingw-w64-clang-x86_64-gettext-tools"
-
       - name: Build MRBind
         if: ${{inputs.mrbind || (inputs.mrbind_c && matrix.build_system == 'CMake') || env.BUILD_C_SHARP == 'true'}}
         shell: cmd
+        env:
+          MSYS2_DIR: C:\msys64
         run: call ./scripts/mrbind/install_mrbind_windows_msys2.bat
 
       - name: Generate C bindings
         if: ${{ (inputs.mrbind_c && matrix.build_system == 'CMake') || env.BUILD_C_SHARP == 'true' }}
         shell: cmd
+        env:
+          MSYS2_DIR: C:\msys64
         # Note that `\` doesn't work here as a line continuation, and will lead to weird errors.
         run: |
           call "${{matrix.vc-path}}\Common7\Tools\VsDevCmd.bat" -arch=amd64 ${{ fromJSON('["", "-vcvars_ver=14.2"]')[matrix.cxx_compiler == 'msvc-2019'] }}
@@ -164,6 +163,8 @@ jobs:
       - name: Generate C# bindings
         if: ${{ env.BUILD_C_SHARP == 'true' }}
         shell: cmd
+        env:
+          MSYS2_DIR: C:\msys64
         # Note that `\` doesn't work here as a line continuation, and will lead to weird errors.
         run: |
           call "${{matrix.vc-path}}\Common7\Tools\VsDevCmd.bat" -arch=amd64 ${{ fromJSON('["", "-vcvars_ver=14.2"]')[matrix.cxx_compiler == 'msvc-2019'] }}
@@ -173,7 +174,7 @@ jobs:
       - name: Build
         shell: cmd
         env:
-          GETTEXT_ROOT: C:\msys64_meshlib_mrbind\clang64
+          GETTEXT_ROOT: C:\msys64\clang64
           VCPKG_ROOT: C:\vcpkg
           VCPKG_TARGET_TRIPLET: ${{ matrix.vcpkg_triplet }}
         # `|| exit /b 1` is used instead of `if errorlevel 1 exit 1`
@@ -194,6 +195,8 @@ jobs:
       - name: Generate and build Python bindings
         if: ${{inputs.mrbind && matrix.vcpkg_triplet != 'x64-windows-meshlib-iterator-debug'}}
         shell: cmd
+        env:
+          MSYS2_DIR: C:\msys64
         # Note that `\` doesn't work here as a line continuation, and will lead to weird errors.
         run: |
           call "${{matrix.vc-path}}\Common7\Tools\VsDevCmd.bat" -arch=amd64 ${{ fromJSON('["", "-vcvars_ver=14.2"]')[matrix.cxx_compiler == 'msvc-2019'] }}

.github/workflows/pip-build.yml

@@ -312,10 +312,14 @@ jobs:
 
       - name: Build MRBind
         shell: cmd
+        env:
+          MSYS2_DIR: C:\msys64
         run: call ./scripts/mrbind/install_mrbind_windows_msys2.bat
 
       - name: Generate and build MRBind bindings
         shell: cmd
+        env:
+          MSYS2_DIR: C:\msys64
         run: |
           call "C:\Program Files\Microsoft Visual Studio\2022\Enterprise\Common7\Tools\VsDevCmd.bat" -arch=amd64
           call ./scripts/mrbind/generate_win.bat -B --trace FOR_WHEEL=1

scripts/mrbind/msys2_package_hashes_clang18.txt

@@ -0,0 +1,49 @@
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