fix(installer): preserve healthy Python runtime and Codex connections

tests/test_install_ps1_reuse_healthy_venv.py

@@ -0,0 +1,77 @@
+"""Run the actual installer functions against a real disposable Python venv."""
+import json
+import os
+import shutil
+import subprocess
+import sys
+from pathlib import Path
+
+import pytest
+
+SOURCE = Path(__file__).resolve().parents[1] / 'scripts/install.ps1'
+PS = shutil.which('powershell') or shutil.which('pwsh')
+pytestmark = pytest.mark.skipif(os.name != 'nt' or not PS, reason='Windows installer runtime test')
+
+
+def function(source, name):
+    start = source.index('function ' + name + ' {')
+    opening = source.index('{', start)
+    depth = 0
+    for index in range(opening, len(source)):
+        if source[index] == '{': depth += 1
+        elif source[index] == '}': depth -= 1
+        if depth == 0: return source[start:index + 1]
+    raise AssertionError(name)
+
+
+@pytest.fixture(scope='module')
+def runtime(tmp_path_factory):
+    root = tmp_path_factory.mktemp('installer-reuse')
+    subprocess.run([sys.executable, '-m', 'venv', '--without-pip', str(root / 'venv')], check=True)
+    return root
+
+
+def run(runtime, body):
+    text = SOURCE.read_text(encoding='utf-8-sig')
+    script = runtime / 'probe.ps1'
+    prefix = "$ErrorActionPreference = 'Stop'\n"
+    prefix += function(text, 'Test-ReusableManagedVenv') + '\n'
+    prefix += function(text, 'Install-Venv') + '\n'
+    prefix += "$InstallDir = '" + str(runtime).replace("'", "''") + "'\n"
+    prefix += "$BasePython = '" + sys._base_executable.replace("'", "''") + "'\n"
+    prefix += "$Version = '" + str(sys.version_info.major) + '.' + str(sys.version_info.minor) + "'\n"
+    script.write_text(prefix + body, encoding='utf-8-sig')
+    result = subprocess.run([PS, '-NoProfile', '-File', str(script)], capture_output=True, text=True, timeout=40)
+    assert result.returncode == 0, result.stdout + result.stderr
+    return result.stdout
+
+
+def test_healthy_update_keeps_live_python_and_never_reaches_kill_sweep(runtime):
+    python = runtime / 'venv/Scripts/python.exe'
+    live = subprocess.Popen([str(python), '-c', 'import time;time.sleep(90)'])
+    try:
+        output = run(runtime, r'''
+function Resolve-AvailablePythonVersion { return @{Path=$BasePython;Version=$Version} }
+function Write-Success { param($Message); Write-Output $Message }
+function Write-Info { throw 'Unexpected venv recreation/kill path' }
+function taskkill { throw 'Live process must not be killed' }
+Install-Venv
+''')
+        assert 'Reusing healthy' in output
+        assert live.poll() is None
+        assert python.is_file()
+    finally:
+        live.terminate();live.wait(timeout=10)
+
+
+def test_wrong_version_or_foreign_interpreter_does_not_reuse(runtime):
+    output = run(runtime, r'''
+$venvPath = Join-Path $InstallDir 'venv'
+$results = @(
+  (Test-ReusableManagedVenv $venvPath $BasePython '0.0'),
+  (Test-ReusableManagedVenv $venvPath (Join-Path $InstallDir 'other-python.exe') $Version),
+  (Test-ReusableManagedVenv (Join-Path $InstallDir 'missing') $BasePython $Version)
+)
+ConvertTo-Json -Compress -InputObject $results
+''')
+    assert json.loads(output) == [False, False, False]