test: skip MPI-launcher run test when libmpi is absent

test_mpirun_launch_imports_mpi forces an mpirun-style env, which makes
shapepipe.run import mpi4py.MPI. On the bare fast-tests runner mpi4py the
package imports but the MPI runtime library (libmpi.so, provided by the
dev image) is missing, so mpi4py.MPI raises RuntimeError — not the
ImportError that pytest.importorskip('mpi4py') guards against. Guard on
importing mpi4py.MPI directly and skip on any failure, matching the
workflow's self-skip pattern for system-dependent tests. The dev-image CI
still exercises the real MPI path. (run.py's launcher gate is unchanged
and correct; test_bare_launch_skips_mpi already passes everywhere.)

Author: claude

tests/module/test_run.py

@@ -50,5 +50,12 @@ def test_bare_launch_skips_mpi():
 
 def test_mpirun_launch_imports_mpi():
     """An mpirun-style env (OMPI_COMM_WORLD_SIZE) must import MPI."""
-    pytest.importorskip("mpi4py")
+    # mpi4py the package may import while the MPI runtime library
+    # (libmpi.so) is absent — that is the case on a bare runner, where the
+    # dev-image-provided MPI is missing. Importing mpi4py.MPI actually loads
+    # libmpi, so skip on its failure (not just a plain ImportError).
+    try:
+        from mpi4py import MPI  # noqa: F401
+    except Exception:
+        pytest.skip("MPI runtime not available (provided by the dev image)")
     assert _import_mpi_flag({"OMPI_COMM_WORLD_SIZE": "1"}) == "True"