test(issue-20): session guard for new entries in the recorded control planes' .mam/jobs and .mam/delegate_job_logs

Watches this checkout's .mam and the ones the recorded binding named. A new entry is a leak when it is an audit log without a registry record, or when its agent_session is missing or not a registered session; live delegations write the record first and target a registered session. Reports, never deletes. The #19 guard's docstring pointed at a #15 session guard that never existed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Sdga4A8i1iSc8DaaW9iKU2

tests/conftest.py

@@ -126,6 +126,10 @@ def _pid_alive(pid):
 # one) reports new entries in the recorded control planes.
 # ==============================================================================
 _REPO_ROOT = Path(__file__).resolve().parent.parent
+_TESTS_DIR = str(Path(__file__).resolve().parent)
+if _TESTS_DIR not in sys.path:
+    sys.path.insert(0, _TESTS_DIR)
+import _mam_state_guard  # noqa: E402
 
 _BINDING_VARS = ("WORKSPACE_ROOT", "AGENT_SESSIONS_YAML", "MAM_JOBS_DIR", "DELEGATE_JOB_LOGS_DIR")
 _RECORDED_BINDING = {}
@@ -1440,10 +1444,27 @@ def _drop_ambient_mam_version():
             os.environ["MAM_VERSION"] = previous
 
 
+@pytest.fixture(scope="session", autouse=True)
+def mam_state_leak_guard(_ambient_control_plane):
+    """Issue #20: no test may leave a record in a real `.mam/jobs` or an audit
+    log in a real `.mam/delegate_job_logs` - this checkout's, or the control
+    plane the ambient binding named before pytest_configure dropped it.
+    Delegations the live system runs meanwhile are told apart by
+    _mam_state_guard.leaks (record first, registered session). The per-test
+    defaults are the fix, this is the regression alarm; it reports and never
+    deletes - these are real control planes. The session registry yaml/db is
+    not hashed: reconcile and create write it during a run."""
+    roots = _mam_state_guard.watch_roots(_REPO_ROOT, _ambient_control_plane)
+    before = _mam_state_guard.snapshot(roots, _ambient_control_plane)
+    yield
+    found = _mam_state_guard.leaks(roots, before, _ambient_control_plane)
+    assert not found, _mam_state_guard.describe(found)
+
+
 @pytest.fixture(scope="session", autouse=True)
 def subscriber_daemon_leak_guard(tmp_path_factory):
     """Issue #19: no `reconcile.sh --subscribe` daemon anchored in this session's
-    pytest basetemp may survive the suite. Mirrors the #15 registry guard: the
+    pytest basetemp may survive the suite. Mirrors the #20 state guard: the
     per-sandbox finalizer is the fix, this is the regression alarm. Leftovers
     are reaped after being reported so a failing run still cleans up."""
     yield