ControlMode(test[regressions]): Track remaining control-mode gaps with strict xfails

why: Document the last failing control-mode behaviors observed in full suite runs.
what:
- Add xfail repros for control-client visibility in attached_sessions, switch_client bad-name handling, multi-var environment propagation, session.kill EOF handling
- Preserve existing env/capture-pane/attached visibility regressions with NamedTuple + test_id parametrization

Author: tony

tests/test_control_mode_regressions.py

@@ -419,3 +419,173 @@ def test_server_kill_handles_control_eof_gracefully() -> None:
     finally:
         with contextlib.suppress(Exception):
             server.kill()
+
+
+#
+# New repros for remaining control-mode failures in full suite
+#
+
+
+class AttachedSessionsFixture(t.NamedTuple):
+    """Fixture for attached_sessions filtering failures."""
+
+    test_id: str
+    expect_empty: bool
+
+
+ATTACHED_SESSIONS_CASES = [
+    pytest.param(
+        AttachedSessionsFixture(
+            test_id="control_client_hidden",
+            expect_empty=True,
+        ),
+        id="attached_control_client_hidden",
+        marks=pytest.mark.xfail(
+            reason="control client still appears in attached_sessions",
+            strict=True,
+        ),
+    ),
+]
+
+
+@pytest.mark.parametrize("case", ATTACHED_SESSIONS_CASES)
+def test_attached_sessions_filters_control_client(
+    case: AttachedSessionsFixture,
+) -> None:
+    """Attached sessions should exclude the control-mode client itself."""
+    socket_name = f"libtmux_test_{uuid.uuid4().hex[:8]}"
+    engine = ControlModeEngine()
+    server = Server(socket_name=socket_name, engine=engine)
+
+    try:
+        # Start a user session; control client should remain hidden.
+        server.new_session(session_name="user_session", attach=False, kill_session=True)
+        attached = server.attached_sessions
+        if case.expect_empty:
+            assert attached == []
+    finally:
+        with contextlib.suppress(Exception):
+            server.kill()
+
+
+class BadSessionNameFixture(t.NamedTuple):
+    """Fixture for switch_client behavior with control client present."""
+
+    test_id: str
+    session_name: str
+    expect_exception: type[BaseException] | None
+
+
+BAD_SESSION_NAME_CASES = [
+    pytest.param(
+        BadSessionNameFixture(
+            test_id="switch_client_should_raise",
+            session_name="hey moo",
+            expect_exception=exc.LibTmuxException,
+        ),
+        id="switch_client_bad_name",
+        marks=pytest.mark.xfail(
+            reason="control client makes switch_client succeed instead of raising",
+            strict=True,
+        ),
+    ),
+]
+
+
+@pytest.mark.parametrize("case", BAD_SESSION_NAME_CASES)
+def test_switch_client_respects_bad_session_names(
+    case: BadSessionNameFixture,
+) -> None:
+    """switch_client should reject invalid names even with control client attached."""
+    socket_name = f"libtmux_test_{uuid.uuid4().hex[:8]}"
+    engine = ControlModeEngine()
+    server = Server(socket_name=socket_name, engine=engine)
+    try:
+        session = server.new_session(
+            session_name="hey moomoo",
+            attach=False,
+            kill_session=True,
+        )
+        assert session is not None
+        assert case.expect_exception is not None
+        with pytest.raises(case.expect_exception):
+            server.switch_client(f"{case.session_name}moo")
+    finally:
+        with contextlib.suppress(Exception):
+            server.kill()
+
+
+class EnvMultiFixture(t.NamedTuple):
+    """Fixture for multi-var environment propagation errors."""
+
+    test_id: str
+    environment: dict[str, str]
+    expected_value: str
+
+
+ENV_MULTI_CASES = [
+    pytest.param(
+        EnvMultiFixture(
+            test_id="new_window_multi_vars",
+            environment={"ENV_VAR_1": "window_1", "ENV_VAR_2": "window_2"},
+            expected_value="window_1",
+        ),
+        id="env_new_window_multi",
+        marks=pytest.mark.xfail(
+            reason="control-mode loses environment with multiple -e flags",
+            strict=True,
+        ),
+    ),
+]
+
+
+@pytest.mark.parametrize("case", ENV_MULTI_CASES)
+def test_environment_multi_var_propagation(case: EnvMultiFixture) -> None:
+    """Multiple -e flags should all be delivered inside the pane."""
+    env = shutil.which("env")
+    assert env is not None
+
+    socket_name = f"libtmux_test_{uuid.uuid4().hex[:8]}"
+    engine = ControlModeEngine()
+    server = Server(socket_name=socket_name, engine=engine)
+
+    try:
+        session = server.new_session(
+            session_name="env_multi_repro",
+            attach=True,
+            window_name="window_with_environment",
+            window_shell=f"{env} PS1='$ ' sh",
+            environment=case.environment,
+            kill_session=True,
+        )
+        pane = session.active_window.active_pane
+        assert pane is not None
+        pane.send_keys("echo $ENV_VAR_1", literal=True, suppress_history=False)
+        output = pane.capture_pane()
+        assert output[-2] == case.expected_value
+    finally:
+        with contextlib.suppress(Exception):
+            server.kill()
+
+
+@pytest.mark.xfail(
+    reason="Session.kill still surfaces ControlModeConnectionError on EOF",
+    strict=True,
+)
+def test_session_kill_handles_control_eof() -> None:
+    """Session.kill should swallow control-mode EOF when tmux exits."""
+    socket_name = f"libtmux_test_{uuid.uuid4().hex[:8]}"
+    engine = ControlModeEngine()
+    server = Server(socket_name=socket_name, engine=engine)
+
+    try:
+        session = server.new_session(
+            session_name="kill_session_repro",
+            attach=False,
+            kill_session=True,
+        )
+        assert session is not None
+        session.kill()
+    finally:
+        with contextlib.suppress(Exception):
+            server.kill()