ci(loader): override pre-set VCPKG_ROOT via GITHUB_ENV

windows-2022 runners with VS Enterprise installed pre-set a
system-wide VCPKG_ROOT pointing at
"C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\vcpkg".
That value wins over the job-level `env: VCPKG_ROOT:` in PowerShell
expansions, so the previous run tried to git-clone into that
read-only path and failed with "destination path ... already exists
and is not an empty directory".

Drop the job-level VCPKG_ROOT and instead resolve the path to
"$GITHUB_WORKSPACE\vcpkg" inside the clone step, then write it
back via GITHUB_ENV so every later step (including Gradle's
findVcpkg / configureNative) picks up our copy. The build step
also dumps VCPKG_ROOT / JAVA_HOME / OPENZEN_BUILD_REVISION up
front for quick diagnosis if the override ever drifts again.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.github/workflows/build-loader.yml

@@ -16,10 +16,12 @@ jobs:
     timeout-minutes: 180
 
     env:
-      VCPKG_ROOT: ${{ github.workspace }}\vcpkg
-      # Push to / pull from the GitHub Actions binary cache so a fresh
-      # checkout reuses already-built Qt instead of rebuilding from
-      # source on every push.
+      # NOTE: do not declare VCPKG_ROOT here. The windows-2022 runner
+      # ships VS Enterprise which pre-sets a system-wide VCPKG_ROOT
+      # pointing at its own (empty) vcpkg dir, and that pre-set value
+      # wins over a job-level env in PowerShell expansions. We export
+      # the right VCPKG_ROOT into $GITHUB_ENV inside the clone step
+      # so every later step sees our copy.
       VCPKG_BINARY_SOURCES: "clear;x-gha,readwrite"
 
     steps:
@@ -61,10 +63,16 @@ jobs:
       - name: Clone & bootstrap vcpkg
         shell: pwsh
         run: |
-          git clone --depth=1 https://github.com/microsoft/vcpkg.git "$env:VCPKG_ROOT"
-          & "$env:VCPKG_ROOT\bootstrap-vcpkg.bat" -disableMetrics
-          Write-Host "vcpkg at $env:VCPKG_ROOT"
-          & "$env:VCPKG_ROOT\vcpkg.exe" version
+          $vcpkg = Join-Path $env:GITHUB_WORKSPACE 'vcpkg'
+          if (Test-Path $vcpkg) {
+              Write-Host "Reusing existing $vcpkg"
+          } else {
+              git clone --depth=1 https://github.com/microsoft/vcpkg.git $vcpkg
+          }
+          & "$vcpkg\bootstrap-vcpkg.bat" -disableMetrics
+          & "$vcpkg\vcpkg.exe" version
+          "VCPKG_ROOT=$vcpkg" | Out-File -FilePath $env:GITHUB_ENV -Encoding utf8 -Append
+          Write-Host "Exported VCPKG_ROOT=$vcpkg to GITHUB_ENV"
 
       - name: Install UPX
         shell: pwsh
@@ -85,6 +93,9 @@ jobs:
         env:
           OPENZEN_BUILD_REVISION: ${{ steps.rev.outputs.sha }}
         run: |
+          Write-Host "VCPKG_ROOT       = $env:VCPKG_ROOT"
+          Write-Host "JAVA_HOME        = $env:JAVA_HOME"
+          Write-Host "OPENZEN_BUILD_REV = $env:OPENZEN_BUILD_REVISION"
           .\gradlew.bat --no-daemon clean dll upxCompress
 
       - name: Show artifact info