Remove mock-awareness from shipped code (production branches on isinstance(..., Mock)) #116

Part of #108 · Phase 2 · This is the highest-value structural fix in the plan.

Problem

Shipped code in clustrix/ knows whether it is being tested and behaves differently.

1. The SLURM status checker branches on Mock

clustrix/executor_scheduler_status.py:89:

from unittest.mock import Mock
is_mock = isinstance(self.connection_manager.ssh_client, Mock) ...
if ... and not is_mock:
    return self._check_slurm_job_status_robust(job_id, active_jobs)
else:
    # Fallback to original logic for unit tests

The comment reads "Use robust checking only if we have a real SSH connection (not unit tests)".

Consequence: _check_slurm_job_status_robust — the code that actually ships to users — is structurally unreachable from any unit test. Every SLURM status test exercises the dead fallback branch instead. The tests are green; the shipped path has never been executed by them.

2. Fake widgets ship in the package

clustrix/notebook_magic_mocks.py defines _MockDropdown, _MockButton, observe(): pass, display(): pass as the ImportError fallback for ipywidgets/IPython. It is imported by six production modules: notebook_magic.py:53, notebook_magic_core.py:15, notebook_magic_widget.py:28, notebook_magic_aws.py:17, notebook_magic_azure.py:17, notebook_magic_gcp.py:18.

So widget code "works" against fake widgets instead of failing loudly when the real dependency is absent — which is precisely the "fallback system" the project's rules prohibit: "Never use mock objects or tests, even as fallback systems — if real functionality doesn't work... they should raise an exception or fail."

Acceptance criteria

• grep -rn "unittest.mock\|MagicMock" clustrix/ returns zero hits
• _check_slurm_job_status_robust is the only SLURM status path; the "original logic for unit tests" fallback is deleted
• A test exercises the robust path against a real (or genuinely simulated-at-the-socket) SSH endpoint, not a Mock
• notebook_magic_mocks.py is deleted. Missing ipywidgets/IPython raises a clear, actionable ImportError naming the extra to install (pip install clustrix[widget]) rather than silently degrading
• A CI check fails the build if unittest.mock is ever imported from clustrix/

Why this is first in Phase 2

Every other de-mocking effort is undermined while production code retains a mock-detecting branch: you can delete a thousand mock assertions and still be testing the wrong code path. Fix the code's awareness of tests before fixing the tests.

Verification

grep -rn "unittest.mock\|MagicMock\|isinstance(.*Mock" clustrix/    # must be empty
python -c "import clustrix.notebook_magic_mocks"                     # must ModuleNotFoundError