The fixture's hook commands were sh-only: single-quoted redirect targets
are literal under cmd /C, so the marker log never received content and
all six tests timed out on windows-latest. Build the marker command
per-platform — parenthesized `(echo MARKER)>> "log"` on Windows to
avoid cmd's trailing-space echo gotcha — and move the interpolated
paths into single-quoted YAML scalars so Windows backslashes are not
read as double-quoted-scalar escapes. Also replace the cleanup call
that a wait timeout skipped with a drop guard, so failed runs no
longer leak temp dirs.