Maity: Board

cli tests: four agent_user/limit cases fail on macOS, also on main

tsk-gvh28gtqjrb3 open

Found by the macOS verification of #1411 (head 9b701728, macOS 27.2, BSD tools). With cd cli && PYTHONPATH=$PWD/src python3 -m pytest tests/test_ssh.py tests/test_agent_user.py -q, four cases fail on main 656ac064 and on the CLI chain alike:

1. tests/test_ssh.py::test_a_limit_on_a_host_is_read_there_and_keeps_its_slot_there, line 531: exit_code is None, 75 expected.
2. tests/test_agent_user.py::test_check_passes_the_agent_user_prerequisites, line 217: maity runner check output lacks "ok maity-agent can run maity".
3. tests/test_agent_user.py::test_the_sandbox_tools_are_found_as_the_agents_user, line 364: sandbox_available is False.
4. tests/test_agent_user.py::test_a_limit_file_is_read_from_the_agents_side_as_their_user, line 383: _limit_exit_code returns None, 75 expected.

Cause not reproduced yet. The test Mac has no maity-agent user; whether that explains all four is a guess. Wanted: find the cause (red with X, green without), then either fix the code or make the tests skip with a stated reason where the prerequisite is missing. Do not hide a real macOS bug behind a skip. CI does not run macOS, so verification goes through the macOS verifier.