ControlMode(test[regressions]): Extend xfail coverage to all known control gaps

why: Capture all currently failing control-mode behaviours in targeted xfail tests before fixing them.
what:
- Add capture_pane prompt repro, environment propagation cases for new-window/split-window, attached_sessions visibility, raise_if_dead bootstrap, and TestServer liveness expectations
- Keep strict xfail markers with NamedTuple test_id parametrization

Author: tony

tests/test_control_mode_regressions.py

@@ -3,6 +3,8 @@
 from __future__ import annotations
 
 import contextlib
+import shutil
+import subprocess
 import typing as t
 import uuid
 
@@ -139,3 +141,191 @@ def test_switch_client_raises_without_user_clients() -> None:
     finally:
         with contextlib.suppress(Exception):
             server.kill()
+
+
+#
+# Integration xfails mirroring observed failures
+#
+
+
+@pytest.mark.xfail(
+    reason="control-mode capture-pane returns trailing blank lines",
+    strict=True,
+)
+def test_capture_pane_returns_only_prompt() -> None:
+    """capture_pane should mirror subprocess trimming and return single prompt line."""
+    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="capture_blank_repro",
+            attach=True,
+            window_shell=f"{env} PS1='$ ' sh",
+            kill_session=True,
+        )
+        pane = session.active_window.active_pane
+        assert pane is not None
+        pane_contents = "\n".join(pane.capture_pane())
+        assert pane_contents == "$"
+    finally:
+        with contextlib.suppress(Exception):
+            server.kill()
+
+
+class EnvPropagationFixture(t.NamedTuple):
+    """Fixture for environment propagation regressions."""
+
+    test_id: str
+    environment: dict[str, str]
+    command: str
+    expected_value: str
+
+
+ENV_PROP_CASES = [
+    pytest.param(
+        EnvPropagationFixture(
+            test_id="new_window_single",
+            environment={"ENV_VAR": "window"},
+            command="echo $ENV_VAR",
+            expected_value="window",
+        ),
+        id="new_window_single",
+        marks=pytest.mark.xfail(
+            reason="control-mode loses environment when creating window",
+            strict=True,
+        ),
+    ),
+    pytest.param(
+        EnvPropagationFixture(
+            test_id="new_window_multiple",
+            environment={"ENV_VAR_1": "window_1", "ENV_VAR_2": "window_2"},
+            command="echo $ENV_VAR_1",
+            expected_value="window_1",
+        ),
+        id="new_window_multiple",
+        marks=pytest.mark.xfail(
+            reason="control-mode loses environment when creating window",
+            strict=True,
+        ),
+    ),
+    pytest.param(
+        EnvPropagationFixture(
+            test_id="split_window_single",
+            environment={"ENV_VAR": "pane"},
+            command="echo $ENV_VAR",
+            expected_value="pane",
+        ),
+        id="split_window_single",
+        marks=pytest.mark.xfail(
+            reason="control-mode loses environment when splitting window",
+            strict=True,
+        ),
+    ),
+    pytest.param(
+        EnvPropagationFixture(
+            test_id="split_window_multiple",
+            environment={"ENV_VAR_1": "pane_1", "ENV_VAR_2": "pane_2"},
+            command="echo $ENV_VAR_1",
+            expected_value="pane_1",
+        ),
+        id="split_window_multiple",
+        marks=pytest.mark.xfail(
+            reason="control-mode loses environment when splitting window",
+            strict=True,
+        ),
+    ),
+]
+
+
+@pytest.mark.parametrize("case", ENV_PROP_CASES)
+def test_environment_propagation(case: EnvPropagationFixture) -> None:
+    """Environment variables should be visible inside panes."""
+    env = shutil.which("env")
+    assert env is not None
+
+    socket_name = f"libtmux_test_{uuid.uuid4().hex[:8]}"
+    engine = ControlModeEngine()
+    server = Server(socket_name=socket_name, engine=engine)
+
+    try:
+        session = server.new_session(
+            session_name=f"env_repro_{case.test_id}",
+            attach=True,
+            window_name="window_with_environment",
+            window_shell=f"{env} PS1='$ ' sh",
+            environment=case.environment,
+            kill_session=True,
+        )
+        pane = session.active_window.active_pane
+        assert pane is not None
+
+        if "split_window" in case.test_id:
+            pane = session.active_window.split(
+                attach=True,
+                environment=case.environment,
+            )
+            assert pane is not None
+
+        pane.send_keys(case.command, 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="control-mode client counts as attached; attached_sessions not empty",
+    strict=True,
+)
+def test_attached_sessions_empty_when_no_clients() -> None:
+    """Attached sessions should be empty on a fresh server."""
+    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="attached_session_repro",
+            attach=True,
+            kill_session=True,
+        )
+        assert session is not None
+        assert server.attached_sessions == []
+    finally:
+        with contextlib.suppress(Exception):
+            server.kill()
+
+
+@pytest.mark.xfail(
+    reason="control-mode is_alive bootstrap hides missing-server errors",
+    strict=True,
+)
+def test_raise_if_dead_raises_on_missing_server() -> None:
+    """raise_if_dead should raise when tmux server does not exist."""
+    socket_name = f"libtmux_test_{uuid.uuid4().hex[:8]}"
+    engine = ControlModeEngine()
+    server = Server(socket_name=socket_name, engine=engine)
+
+    with pytest.raises(subprocess.CalledProcessError):
+        server.raise_if_dead()
+
+
+@pytest.mark.xfail(
+    reason="TestServer with control engine starts server eagerly",
+    strict=True,
+)
+def test_testserver_is_alive_false_before_use() -> None:
+    """TestServer should report not alive before first use."""
+    engine = ControlModeEngine()
+    server = Server(socket_name=f"libtmux_test_{uuid.uuid4().hex[:8]}", engine=engine)
+    try:
+        assert server.is_alive() is False
+    finally:
+        with contextlib.suppress(Exception):
+            server.kill()