Session(feat[new_window]): add kill-existing and select-existing flags

why: new-window supports flags for replacing existing windows at a target
index and selecting existing windows by name that were not exposed.
what:
- Add kill_existing (-k) and select_existing (-S) parameters to new_window()
- -k destroys existing window at target index before creating new one
- -S selects existing window with matching name instead of creating new
- Add tests for both flags

Author: tony

src/libtmux/session.py

@@ -461,6 +461,8 @@ def new_window(
         environment: dict[str, str] | None = None,
         direction: WindowDirection | None = None,
         target_window: str | None = None,
+        kill_existing: bool | None = None,
+        select_existing: bool | None = None,
     ) -> Window:
         """Create new window, returns new :class:`Window`.
 
@@ -491,6 +493,16 @@ def new_window(
 
         target_window : str, optional
             Used by :meth:`Window.new_window` to specify the target window.
+        kill_existing : bool, optional
+            Destroy the window at the target index if it already exists
+            (``-k`` flag).
+
+            .. versionadded:: 0.45
+        select_existing : bool, optional
+            If a window with the given name already exists, select it instead
+            of creating a new one (``-S`` flag).
+
+            .. versionadded:: 0.45
 
         .. versionchanged:: 0.28.0
 
@@ -555,6 +567,12 @@ def new_window(
         if direction is not None:
             window_args += (WINDOW_DIRECTION_FLAG_MAP[direction],)
 
+        if kill_existing:
+            window_args += ("-k",)
+
+        if select_existing:
+            window_args += ("-S",)
+
         target: str | None = None
         if window_index is not None:
             # empty string for window_index will use the first one available

tests/test_session.py

@@ -574,3 +574,36 @@ def patched_cmd(cmd_name: str, *args: t.Any, **kwargs: t.Any) -> tmux_cmd:
     )
     with raises_ctx:
         test_session.attach()
+
+
+def test_new_window_kill_existing(session: Session) -> None:
+    """Test Session.new_window() with kill_existing flag."""
+    # Create a window at a specific index
+    w1 = session.new_window(window_name="kill_orig", window_index="5")
+    assert w1.window_name == "kill_orig"
+    assert w1.window_index == "5"
+
+    # Create another window at the same index with kill_existing
+    w2 = session.new_window(
+        window_name="kill_replace",
+        window_index="5",
+        kill_existing=True,
+    )
+    assert w2.window_name == "kill_replace"
+    assert w2.window_index == "5"
+
+    # Original window should be gone
+    session.refresh()
+    names = [w.window_name for w in session.windows]
+    assert "kill_orig" not in names
+    assert "kill_replace" in names
+
+
+def test_new_window_select_existing(session: Session) -> None:
+    """Test Session.new_window() with select_existing flag — new name."""
+    # With a unique name and select_existing, a new window is created normally
+    w = session.new_window(
+        window_name="selexist_new",
+        select_existing=True,
+    )
+    assert w.window_name == "selexist_new"