fix(test-runner): preserve PATHEXT for native PowerShell children

scripts/run_tests.sh

@@ -113,12 +113,14 @@ fi
 # resolves Path.home() from USERPROFILE (or HOMEDRIVE+HOMEPATH), stdlib
 # platform paths come from LOCALAPPDATA/APPDATA, ssl/sockets need SYSTEMROOT,
 # and tempfile needs TEMP/TMP. Dropping them breaks collection on native
-# Windows (issues #67385, #70813). These are location variables, not
+# Windows (issues #67385, #70813). PATHEXT is also required: without .EXE,
+# PowerShell can return success without executing a native child.
+# These are location variables, not
 # credentials, so forwarding them keeps the isolation intent intact. Each is
 # only forwarded when actually set, so POSIX runs are byte-for-byte unchanged.
 WIN_ENV=()
 for _win_var in USERPROFILE HOMEDRIVE HOMEPATH LOCALAPPDATA APPDATA SYSTEMROOT TEMP TMP \
-    ComSpec PROGRAMFILES ProgramFiles PROGRAMDATA ProgramData; do
+    ComSpec PATHEXT PROGRAMFILES ProgramFiles PROGRAMDATA ProgramData; do
   if [ -n "${!_win_var:-}" ]; then
     WIN_ENV+=("$_win_var=${!_win_var}")
   fi