ci(build): resolve Python via py launcher on VM217 windows lane

VM217 runner-service PATH exposes neither conan nor a bare python
(setup-python is gated off for self-hosted), so python -m pip hit
CommandNotFoundException. Resolve an interpreter ourselves (py ->
python3 -> python) with where.exe diagnostics on miss, and fix the
unquoted sysconfig.get_path(scripts) NameError.

Author: frstrtr

.github/workflows/build.yml

@@ -751,14 +751,26 @@ jobs:
         # fork-fallback windows-2022 has it too). Inherits the job-level
         # ExecutionPolicy-Bypass shell (see defaults above).
         run: |
-          # VM217 runner-service PATH does NOT include conan: pip drops it in a
-          # Scripts dir that is not on PATH, so "conan --version" hit
-          # CommandNotFoundException even though Python 3.12 is present. Install
-          # unconditionally and export the pip Scripts dir(s) via GITHUB_PATH so
-          # this step and later steps (Detect profile / Conan install) resolve it.
-          python -m pip install "conan>=2.0,<3.0"
-          $scripts = & python -c "import sysconfig; print(sysconfig.get_path(scripts))"
-          $userScripts = & python -c "import sysconfig; print(sysconfig.get_path(scripts,nt_user))"
+          # VM217 runner-service PATH exposes neither conan nor a bare python:
+          # setup-python is gated off for self-hosted, so resolve an interpreter
+          # ourselves. The Windows py launcher (C:\Windows, on PATH for all
+          # users) is the reliable entry point; fall back py -> python3 -> python
+          # and dump where.exe diagnostics if none resolve. Then pip-install conan
+          # and export its Scripts dir(s) via GITHUB_PATH for later steps.
+          $py = $null
+          foreach ($cand in @('py','python3','python')) {
+            if (Get-Command $cand -ErrorAction SilentlyContinue) { $py = $cand; break }
+          }
+          if (-not $py) {
+            Write-Host "No Python interpreter on PATH. Diagnostics:"
+            & where.exe python 2>&1; & where.exe py 2>&1; & where.exe python3 2>&1
+            Write-Host "PATH=$env:PATH"
+            throw "VM217 has no Python interpreter on the runner-service PATH"
+          }
+          Write-Host "Using interpreter: $py"
+          & $py -m pip install "conan>=2.0,<3.0"
+          $scripts = & $py -c "import sysconfig; print(sysconfig.get_path('scripts'))"
+          $userScripts = & $py -c "import sysconfig; print(sysconfig.get_path('scripts','nt_user'))"
           $env:PATH = "$scripts;$userScripts;$env:PATH"
           Add-Content -Path $env:GITHUB_PATH -Value $scripts
           Add-Content -Path $env:GITHUB_PATH -Value $userScripts