docs(doctests): annotate untestable interactive commands

why: display_menu, display_popup, and display_message have paths
that require TTY-backed clients or render in the status line,
making them not programmatically verifiable. Adding explicit notes
prevents false positives from agents and reviewers.
what:
- Add "Not directly testable" note to display_menu doctest
- Add "Not directly testable" note to display_popup doctest
- Add note about get_text=False path in display_message docstring

Author: tony

src/libtmux/pane.py

@@ -621,6 +621,8 @@ def display_message(
         """Display message to pane.
 
         Displays a message in target-client status line.
+        The ``get_text=False`` path renders in the status line and is not
+        programmatically verifiable; only ``get_text=True`` returns output.
 
         Parameters
         ----------
@@ -1192,6 +1194,10 @@ def display_popup(
 
         Examples
         --------
+        Not directly testable — popup rendering requires a TTY-backed client.
+        Control-mode provides an attached client for invocation but the popup
+        itself is not visible or verifiable.
+
         >>> with control_mode() as ctl:
         ...     pane.display_popup(command='true', close_on_exit=True)
         """

src/libtmux/server.py

@@ -1019,6 +1019,10 @@ def display_menu(
 
         Examples
         --------
+        Not directly testable — requires a TTY-backed client.
+        Control-mode clients set ``tty.sy=0``, causing ``menu_prepare()``
+        to return NULL inside tmux.
+
         >>> server.display_menu  # doctest: +ELLIPSIS
         <bound method ...>
         """