ControlModeEngine(test[flags]): cover client flags, flow, subscriptions

why: Guard new control-mode helper API with deterministic unit coverage.

what:
- Expand set_client_flags cases to tmux !flag semantics and new flags
- Validate pause-after non-negative and bad flow states
- Add set_pane_flow and subscribe/unsubscribe argument construction tests

Author: tony

tests/test_control_mode_engine.py

@@ -344,7 +344,25 @@ class SetClientFlagsCase(t.NamedTuple):
         SetClientFlagsCase(
             test_id="disable_no_output_clear_pause",
             kwargs={"no_output": False, "pause_after": 0},
-            expected_flags={"no-output=off", "pause-after=none"},
+            expected_flags={"!no-output", "!pause-after"},
+            expect_run=True,
+        ),
+        SetClientFlagsCase(
+            test_id="wait_exit_and_read_only",
+            kwargs={"wait_exit": True, "read_only": True},
+            expected_flags={"wait-exit", "read-only"},
+            expect_run=True,
+        ),
+        SetClientFlagsCase(
+            test_id="clear_wait_exit",
+            kwargs={"wait_exit": False},
+            expected_flags={"!wait-exit"},
+            expect_run=True,
+        ),
+        SetClientFlagsCase(
+            test_id="toggle_misc_flags",
+            kwargs={"ignore_size": True, "active_pane": False},
+            expected_flags={"ignore-size", "!active-pane"},
             expect_run=True,
         ),
         SetClientFlagsCase(
@@ -395,6 +413,141 @@ def fake_run(
     assert server_args == ()
 
 
+def test_set_client_flags_rejects_negative_pause() -> None:
+    """pause_after must be non-negative."""
+    engine = ControlModeEngine(start_threads=False)
+    with pytest.raises(ValueError):
+        engine.set_client_flags(pause_after=-1)
+
+
+class PaneFlowCase(t.NamedTuple):
+    """Fixture for refresh-client -A flow control."""
+
+    test_id: str
+    pane_id: str | int
+    state: str
+    expected_arg: str
+
+
+@pytest.mark.parametrize(
+    "case",
+    [
+        PaneFlowCase(
+            test_id="resume_default",
+            pane_id="%1",
+            state="continue",
+            expected_arg="%1:continue",
+        ),
+        PaneFlowCase(
+            test_id="pause_pane",
+            pane_id=3,
+            state="pause",
+            expected_arg="3:pause",
+        ),
+    ],
+    ids=lambda c: c.test_id,
+)
+def test_set_pane_flow_builds_refresh_client(case: PaneFlowCase) -> None:
+    """set_pane_flow should build refresh-client -A args."""
+    engine = ControlModeEngine(start_threads=False)
+    calls: list[tuple[str, tuple[str, ...], tuple[str, ...]]] = []
+
+    class DummyCmd:
+        stdout: t.ClassVar[list[str]] = []
+        stderr: t.ClassVar[list[str]] = []
+        returncode: t.ClassVar[int] = 0
+
+    def fake_run(
+        cmd: str,
+        cmd_args: t.Sequence[str | int] | None = None,
+        server_args: t.Sequence[str | int] | None = None,
+        timeout: float | None = None,
+    ) -> DummyCmd:
+        cmd_args_tuple = tuple(str(a) for a in (cmd_args or ()))
+        server_args_tuple = tuple(str(a) for a in (server_args or ()))
+        calls.append((cmd, cmd_args_tuple, server_args_tuple))
+        return DummyCmd()
+
+    engine.run = fake_run  # type: ignore[assignment]
+
+    engine.set_pane_flow(case.pane_id, state=case.state)
+
+    assert calls
+    cmd, cmd_args, server_args = calls[0]
+    assert cmd == "refresh-client"
+    assert cmd_args == ("-A", case.expected_arg)
+    assert server_args == ()
+
+
+def test_set_pane_flow_validates_state() -> None:
+    """Invalid flow state should raise."""
+    engine = ControlModeEngine(start_threads=False)
+    with pytest.raises(ValueError):
+        engine.set_pane_flow("%1", state="bad")
+
+
+class SubscribeCase(t.NamedTuple):
+    """Fixture for refresh-client -B subscription arguments."""
+
+    test_id: str
+    name: str
+    what: str | None
+    format: str | None
+    expected_args: tuple[str, ...]
+
+
+@pytest.mark.parametrize(
+    "case",
+    [
+        SubscribeCase(
+            test_id="add_subscription",
+            name="focus",
+            what="%1",
+            format="#{pane_active}",
+            expected_args=("-B", "focus:%1:#{pane_active}"),
+        ),
+        SubscribeCase(
+            test_id="remove_subscription",
+            name="focus",
+            what=None,
+            format=None,
+            expected_args=("-B", "focus"),
+        ),
+    ],
+    ids=lambda c: c.test_id,
+)
+def test_subscribe_builds_refresh_client(case: SubscribeCase) -> None:
+    """Subscribe should wrap refresh-client -B calls."""
+    engine = ControlModeEngine(start_threads=False)
+    calls: list[tuple[str, tuple[str, ...], tuple[str, ...]]] = []
+
+    class DummyCmd:
+        stdout: t.ClassVar[list[str]] = []
+        stderr: t.ClassVar[list[str]] = []
+        returncode: t.ClassVar[int] = 0
+
+    def fake_run(
+        cmd: str,
+        cmd_args: t.Sequence[str | int] | None = None,
+        server_args: t.Sequence[str | int] | None = None,
+        timeout: float | None = None,
+    ) -> DummyCmd:
+        cmd_args_tuple = tuple(str(a) for a in (cmd_args or ()))
+        server_args_tuple = tuple(str(a) for a in (server_args or ()))
+        calls.append((cmd, cmd_args_tuple, server_args_tuple))
+        return DummyCmd()
+
+    engine.run = fake_run  # type: ignore[assignment]
+
+    engine.subscribe(case.name, what=case.what, fmt=case.format)
+
+    assert calls
+    cmd, cmd_args, server_args = calls[0]
+    assert cmd == "refresh-client"
+    assert cmd_args == case.expected_args
+    assert server_args == ()
+
+
 class ScriptedStdin:
     """Fake stdin that can optionally raise BrokenPipeError on write."""