Fix install.ps1 Python probe crash on PowerShell 5.1

CHANGELOG.md

@@ -4,6 +4,15 @@ All notable changes to Looper are documented here. Versions follow
 [Semantic Versioning](https://semver.org/); the loop spec format is versioned
 separately via `version:` in `loop.yaml` (currently `1`).
 
+## 0.2.1 — 2026-07-05
+
+### Fixed
+- `install.ps1` crashed on Windows PowerShell 5.1 with "Argument expected for
+  the -c option": the Python probe passed an empty string (which PowerShell
+  drops for native executables) and its stderr redirect became a terminating
+  error under the script's `Stop` preference. The probe now runs `--version`
+  with stderr tolerated and validates the exit code (#14).
+
 ## 0.2.0 — 2026-07-05
 
 Remediation release from a full audit of the runner, compiler, installers,

install.ps1

@@ -16,15 +16,25 @@ if (-not (Get-Command git -ErrorAction SilentlyContinue)) {
 
 # Validate by executing, not just locating: on Windows, "python" on PATH is
 # often the Microsoft Store alias stub, which exists but cannot run scripts.
+# The probe must tolerate stub stderr output without tripping the script's
+# ErrorActionPreference = "Stop".
 $Python = $null
 foreach ($Candidate in @("python", "py")) {
     $Command = Get-Command $Candidate -ErrorAction SilentlyContinue
-    if ($Command) {
-        & $Command.Source -c "" 2>$null
-        if ($LASTEXITCODE -eq 0) {
-            $Python = $Command
-            break
-        }
+    if (-not $Command) { continue }
+    $PreviousEAP = $ErrorActionPreference
+    $ErrorActionPreference = "Continue"
+    try {
+        $null = & $Command.Source --version 2>&1
+        $Works = ($LASTEXITCODE -eq 0)
+    } catch {
+        $Works = $false
+    } finally {
+        $ErrorActionPreference = $PreviousEAP
+    }
+    if ($Works) {
+        $Python = $Command
+        break
     }
 }
 if (-not $Python) {

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "looper-skill"
-version = "0.2.0"
+version = "0.2.1"
 description = "A Claude Code skill that scaffolds well-designed agent loops."
 readme = "README.md"
 requires-python = ">=3.9"