test(installer): guard Ensure-NodeExeOnPath wiring in install.ps1

Regression tests assert the helper exists and is invoked from Test-Node and
Install-NodeDeps before any npm install on Windows.

tests/test_install_ps1_node_path_for_npm.py

@@ -0,0 +1,43 @@
+"""Regression tests for #48130: Windows npm lifecycle scripts need node on PATH.
+
+The desktop installer can resolve ``npm.cmd`` while postinstall hooks fail with
+``'node' is not recognized`` because child ``cmd.exe`` processes do not inherit
+a PATH that includes ``node.exe``'s directory.
+"""
+
+from __future__ import annotations
+
+import re
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parent.parent
+INSTALL_PS1 = REPO_ROOT / "scripts" / "install.ps1"
+
+
+def _install_ps1() -> str:
+    return INSTALL_PS1.read_text(encoding="utf-8")
+
+
+def test_install_ps1_defines_ensure_node_exe_on_path_helper() -> None:
+    text = _install_ps1()
+    assert "function Ensure-NodeExeOnPath" in text
+    assert re.search(
+        r"\$env:Path\s*=\s*\"\$nodeExeDir;\$env:Path\"",
+        text,
+    ), "Ensure-NodeExeOnPath must prepend node.exe's directory to PATH"
+
+
+def test_test_node_prepends_node_dir_before_success() -> None:
+    text = _install_ps1()
+    assert re.search(
+        r"if \(Test-NodeVersionOk \$version\) \{[\s\S]{0,200}?Ensure-NodeExeOnPath",
+        text,
+    ), "Test-Node must call Ensure-NodeExeOnPath when a system Node passes the version floor"
+
+
+def test_install_node_deps_prepends_node_dir_before_npm() -> None:
+    text = _install_ps1()
+    assert re.search(
+        r"function Install-NodeDeps \{[\s\S]{0,900}?Ensure-NodeExeOnPath[\s\S]{0,900}?Resolve npm explicitly",
+        text,
+    ), "Install-NodeDeps must call Ensure-NodeExeOnPath before invoking npm"