fix(ci): use vswhere to locate and activate MSVC for x86 on windows-2025

The x86 (32-bit) build fails at Install dependencies because packages
such as pyyaml and greenlet have no cp314-win32 wheels and must be
built from sdist, requiring a 32-bit MSVC toolchain.

Root cause on current runners:
- windows-2025 now ships Visual Studio 2026 (paths under
  Microsoft Visual Studio\18\Enterprise, not 2022).
- Previous hardcoded "2022" discovery failed to locate vcvarsall.bat.
- ilammy/msvc-dev-cmd is Node-20 based and deprecated on Node 24.

Proper solution (standard in GitHub Actions + VS 2022/2026 CI):
- Use vswhere.exe (official locator) to dynamically find the current
  installationPath (handles any VS version/edition).
- Activate with amd64_x86 (64-bit host tools for 32-bit target).
- Verify in logs (where cl + version output).
- Export env (PATH/INCLUDE/LIB) via GITHUB_ENV for uv sync --compile.

Implemented with pwsh + child cmd for vcvars (no external action).

Only this CI x86 fix; no dep changes.

Author: AAClause

.github/workflows/build_app.yml

@@ -44,6 +44,35 @@ jobs:
         with:
           python-version: 'cpython-3.14-windows-${{ matrix.arch }}-none'
           working-directory: ${{ github.workspace }}/repo
+      - name: Setup MSVC for x86
+        if: matrix.arch == 'x86'
+        shell: pwsh
+        run: |
+          $ErrorActionPreference = 'Stop'
+          $vswhere = "${env:ProgramFiles(x86)}\Microsoft Visual Studio\Installer\vswhere.exe"
+          if (-not (Test-Path $vswhere)) {
+            throw "vswhere.exe not found at $vswhere"
+          }
+          $installPath = & $vswhere -latest -products * -property installationPath 2>$null | Select-Object -First 1
+          if (-not $installPath) {
+            throw "vswhere did not return an installation path"
+          }
+          $vcvarsall = Join-Path $installPath 'VC\Auxiliary\Build\vcvarsall.bat'
+          if (-not (Test-Path $vcvarsall)) {
+            throw "vcvarsall.bat not found at $vcvarsall (installPath=$installPath)"
+          }
+          Write-Host "Using vcvarsall: $vcvarsall"
+
+          # Activate and verify in a child cmd (prints to logs)
+          cmd /c "`"$vcvarsall`" amd64_x86 && echo === Verifying 32-bit MSVC (for uv sdist win32 builds) === && where cl && cl 2>&1 | findstr /C:Version && echo ============================================"
+
+          # Export environment for subsequent steps
+          cmd /c "`"$vcvarsall`" amd64_x86 && set" | ForEach-Object {
+            if ($_ -match '^(.*?)=(.*)$') {
+              Add-Content -Path $env:GITHUB_ENV -Value "$($matches[1])=$($matches[2])" -Encoding utf8
+            }
+          }
+          Write-Host "MSVC x86 environment exported to GITHUB_ENV"
       - name: Install dependencies
         working-directory: ${{ github.workspace }}/repo
         run: uv sync --frozen --compile --group build --group test