Windows: resolve process image paths with one Win32_Process query

install.ps1's venv-holder probe opened a handle to every running PID through
inline C# compiled at runtime. Opening a handle per process is a shape AV
heuristics score hard, and it bought nothing: Win32_Process reports
ExecutablePath for exactly the processes those handles could be opened against,
and answers for all of them in a single query instead of once per PID.

The remaining file-canonicalisation imports stay -- handle-based resolution of
linked ancestors has no faithful Windows PowerShell 5.1 equivalent, and it runs
on security-relevant paths.

Falls back to the per-process .Path when the query is unavailable, so a degraded
WMI repository degrades exactly as the old code did on a process it could not
open.

.github/workflows/studio-windows-inference-smoke.yml

@@ -131,6 +131,8 @@ jobs:
           if ($LASTEXITCODE) { exit $LASTEXITCODE }
           pwsh -NoProfile -File tests/studio/test_path_probe_access_denied.ps1
           if ($LASTEXITCODE) { exit $LASTEXITCODE }
+          pwsh -NoProfile -File tests/studio/test_process_image_path_map.ps1
+          if ($LASTEXITCODE) { exit $LASTEXITCODE }
 
       # uninstall.ps1: native uninstall must keep the shared unsloth.ico while a
       # WSL shortcut still references it (dual install), else that shortcut blanks.

install.ps1

@@ -440,22 +440,6 @@ public static class UnslothStudioFinalPathV2
         uint pathLength,
         uint flags);
 
-    [DllImport("kernel32.dll", SetLastError = true)]
-    private static extern IntPtr OpenProcess(
-        uint desiredAccess,
-        bool inheritHandle,
-        int processId);
-
-    [DllImport("kernel32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
-    private static extern bool QueryFullProcessImageNameW(
-        IntPtr process,
-        uint flags,
-        StringBuilder path,
-        ref uint pathLength);
-
-    [DllImport("kernel32.dll", SetLastError = true)]
-    private static extern bool CloseHandle(IntPtr handle);
-
     public static string Resolve(string path)
     {
         using (SafeFileHandle handle = CreateFileW(
@@ -488,28 +472,6 @@ public static class UnslothStudioFinalPathV2
             return buffer.ToString();
         }
   }
-
-    public static string GetProcessImagePath(int processId)
-    {
-        const uint ProcessQueryLimitedInformation = 0x1000;
-        IntPtr process = OpenProcess(ProcessQueryLimitedInformation, false, processId);
-        if (process == IntPtr.Zero)
-        {
-            return null;
-        }
-        try
-        {
-            StringBuilder path = new StringBuilder(32768);
-            uint pathLength = (uint)path.Capacity;
-            return QueryFullProcessImageNameW(process, 0, path, ref pathLength)
-                ? path.ToString()
-                : null;
-        }
-        finally
-        {
-            CloseHandle(process);
-        }
-  }
 }
 '@
         }
@@ -1906,6 +1868,23 @@ exit 0
         }
     }
 
+    # PID -> image path for every process this user can see, in ONE query. This used to open a
+    # handle to every running PID through the inline C# type above, which is a shape AV
+    # heuristics score hard and bought nothing here: Win32_Process reports ExecutablePath for
+    # exactly the processes that could be opened, and answers for all of them at once.
+    function Get-StudioProcessImagePathMap {
+        $map = @{}
+        try {
+            foreach ($entry in @(Get-CimInstance Win32_Process -ErrorAction Stop)) {
+                if ($entry.ExecutablePath) { $map[[int]$entry.ProcessId] = $entry.ExecutablePath }
+            }
+        } catch {
+            # A degraded WMI repository leaves the map empty; the per-process .Path fallback
+            # below still resolves the accessible ones.
+        }
+        return $map
+    }
+
     function Get-RunningStudioVenvProcesses {
         param(
             [Parameter(Mandatory = $true)][string]$VenvPath,
@@ -1917,11 +1896,18 @@ exit 0
             throw "Could not resolve managed Studio process path '$VenvPath': $($_.Exception.Message)"
         }
 
+        $imagePaths = Get-StudioProcessImagePathMap
+
         # Block only confirmed executable identities: a command line or working
         # directory that merely mentions the path is not proof of an open file.
         foreach ($process in @(Get-Process -ErrorAction SilentlyContinue)) {
             $executable = $null
-            try { $executable = [UnslothStudioFinalPathV2]::GetProcessImagePath($process.Id) } catch { continue }
+            if ($imagePaths.ContainsKey([int]$process.Id)) { $executable = $imagePaths[[int]$process.Id] }
+            # .Path reads MainModule, which needs rights Win32_Process does not: only a fallback,
+            # and a protected or cross-bitness process throws here exactly as it did before.
+            if (-not $executable) {
+                try { $executable = $process.Path } catch { continue }
+            }
             if (-not $executable) { continue }
             try { $executable = Get-StudioFinalPath -Path $executable } catch { continue }
             if (Test-StudioProtectedPathMatch -Candidate $executable -ProtectedPath $resolvedPath -Exact:$Exact) {

tests/studio/test_process_image_path_map.ps1

@@ -0,0 +1,58 @@
+# Regression tests for install.ps1's venv-holder probe.
+#
+# Resolving a PID to its image path used to open a handle to every running process from inline
+# C# compiled at runtime -- a shape AV heuristics score hard, on top of the csc.exe compile the
+# type already costs. Win32_Process answers the same question for the same set of processes in
+# one query, so the pair was removed. These tests pin both halves: the P/Invoke must stay gone,
+# and the replacement must actually resolve a real process.
+$ErrorActionPreference = "Stop"
+$script:failures = 0
+function Check($name, $cond) {
+    if ($cond) { Write-Host "  PASS  $name" }
+    else { Write-Host "  FAIL  $name" -ForegroundColor Red; $script:failures++ }
+}
+
+$repoRoot = (Resolve-Path ([System.IO.Path]::Combine($PSScriptRoot, "..", ".."))).Path
+$installPath = [System.IO.Path]::Combine($repoRoot, "install.ps1")
+$installText = Get-Content -Raw -LiteralPath $installPath
+
+# ── Source contract ──
+Check "install.ps1 no longer opens a handle per PID from inline C#" (
+    $installText -notmatch 'private static extern IntPtr OpenProcess')
+Check "install.ps1 no longer imports the image-path query" (
+    $installText -notmatch 'QueryFullProcessImageNameW')
+Check "the inline type still resolves final paths" (
+    $installText -match 'GetFinalPathNameByHandleW')
+Check "the venv-holder probe reads the prefetched map" (
+    $installText -match '\$imagePaths = Get-StudioProcessImagePathMap')
+Check "one Win32_Process query, not one per PID" (
+    ([regex]::Matches($installText, 'Get-CimInstance Win32_Process')).Count -eq 1)
+
+# ── Behaviour ──
+. ([System.IO.Path]::Combine($repoRoot, "tests", "studio_setup_ps1", "Get-FunctionSource.ps1"))
+$src = Get-FunctionSource -Path $installPath -Name "Get-StudioProcessImagePathMap"
+Check "install.ps1 defines Get-StudioProcessImagePathMap" ($null -ne $src)
+
+if ($src -and $IsWindows -ne $false) {
+    . ([scriptblock]::Create($src))
+    $map = Get-StudioProcessImagePathMap
+    Check "the map is a hashtable" ($map -is [hashtable])
+    # This process is running an interpreter off disk, so it must resolve.
+    $own = $PID
+    Check "the map resolves this process to an image path" (
+        $map.ContainsKey([int]$own) -and $map[[int]$own])
+    if ($map.ContainsKey([int]$own)) {
+        Check "the resolved image path exists on disk" (Test-Path -LiteralPath $map[[int]$own])
+    }
+    # Every value must be a path, never a bare process name: the venv match compares full paths.
+    $bad = @($map.Values | Where-Object { $_ -and -not ([System.IO.Path]::IsPathRooted($_)) })
+    Check "every resolved image path is rooted" ($bad.Count -eq 0)
+} else {
+    Write-Host "  SKIP  runtime map checks (Win32_Process is Windows-only)"
+}
+
+if ($script:failures -gt 0) {
+    Write-Host "$($script:failures) check(s) failed" -ForegroundColor Red
+    exit 1
+}
+Write-Host "All checks passed"