fix(tui): guard app-level UI work with is_running

StrixTUIApp subclasses textual.app.App, whose is_mounted is a method taking a widget, not the Widget.is_mounted property. A bare self.is_mounted is a bound method object and always truthy, so every if-not-self.is_mounted guard was dead code.

Switch the 13 app-level lifecycle checks to App.is_running. Add regression coverage that verifies the Textual API distinction, locks all 13 replacements, and proves a stopped StrixTUIApp action returns before querying the widget tree.

strix/interface/tui/app.py

@@ -867,7 +867,7 @@ class StrixTUIApp(App):  # type: ignore[misc]
             yield SplashScreen(id="splash_screen")
 
     def watch_show_splash(self, show_splash: bool) -> None:
-        if not show_splash and self.is_mounted:
+        if not show_splash and self.is_running:
             try:
                 splash = self.query_one("#splash_screen")
                 splash.remove()
@@ -939,7 +939,7 @@ class StrixTUIApp(App):  # type: ignore[misc]
         if len(self.screen_stack) > 1 or self.show_splash:
             return
 
-        if not self.is_mounted:
+        if not self.is_running:
             return
 
         try:
@@ -954,7 +954,7 @@ class StrixTUIApp(App):  # type: ignore[misc]
         if len(self.screen_stack) > 1 or self.show_splash:
             return
 
-        if not self.is_mounted:
+        if not self.is_running:
             return
 
         try:
@@ -986,7 +986,7 @@ class StrixTUIApp(App):  # type: ignore[misc]
         if len(self.screen_stack) > 1:
             return
 
-        if not self.is_mounted:
+        if not self.is_running:
             return
 
         try:
@@ -1110,7 +1110,7 @@ class StrixTUIApp(App):  # type: ignore[misc]
         return self._get_rendered_events_content(events), "chat-content"
 
     def _update_chat_view(self) -> None:
-        if len(self.screen_stack) > 1 or self.show_splash or not self.is_mounted:
+        if len(self.screen_stack) > 1 or self.show_splash or not self.is_running:
             return
 
         try:
@@ -1467,7 +1467,7 @@ class StrixTUIApp(App):  # type: ignore[misc]
         if len(self.screen_stack) > 1 or self.show_splash:
             return
 
-        if not self.is_mounted:
+        if not self.is_running:
             return
 
         self._displayed_events.clear()
@@ -1542,7 +1542,7 @@ class StrixTUIApp(App):  # type: ignore[misc]
         if len(self.screen_stack) > 1 or self.show_splash:
             return
 
-        if not self.is_mounted:
+        if not self.is_running:
             return
 
         agent_id = agent_data["id"]
@@ -1679,7 +1679,7 @@ class StrixTUIApp(App):  # type: ignore[misc]
         if len(self.screen_stack) > 1 or self.show_splash:
             return
 
-        if not self.is_mounted:
+        if not self.is_running:
             return
 
         node = event.node
@@ -1699,7 +1699,7 @@ class StrixTUIApp(App):  # type: ignore[misc]
         if len(self.screen_stack) > 1 or self.show_splash:
             return
 
-        if not self.is_mounted:
+        if not self.is_running:
             return
 
         node = event.node
@@ -1748,7 +1748,7 @@ class StrixTUIApp(App):  # type: ignore[misc]
         return "Unknown Agent"
 
     def action_toggle_help(self) -> None:
-        if self.show_splash or not self.is_mounted:
+        if self.show_splash or not self.is_running:
             return
 
         try:
@@ -1766,7 +1766,7 @@ class StrixTUIApp(App):  # type: ignore[misc]
         self.push_screen(HelpScreen())
 
     async def action_request_quit(self) -> None:
-        if self.show_splash or not self.is_mounted:
+        if self.show_splash or not self.is_running:
             await self.action_custom_quit()
             return
 
@@ -1782,7 +1782,7 @@ class StrixTUIApp(App):  # type: ignore[misc]
         self.push_screen(QuitScreen())
 
     def action_stop_selected_agent(self) -> None:
-        if self.show_splash or not self.is_mounted:
+        if self.show_splash or not self.is_running:
             return
 
         if len(self.screen_stack) > 1:
@@ -1941,7 +1941,7 @@ class StrixTUIApp(App):  # type: ignore[misc]
             return True
 
     def on_resize(self, event: events.Resize) -> None:
-        if self.show_splash or not self.is_mounted:
+        if self.show_splash or not self.is_running:
             return
 
         try:

tests/test_tui_mount_guard.py

@@ -0,0 +1,78 @@
+"""Regression tests for the TUI's app-lifecycle guards.
+
+``StrixTUIApp`` subclasses ``textual.app.App``, whose ``is_mounted`` is a
+*method* taking a widget — not the ``Widget.is_mounted`` property. A bare
+``self.is_mounted`` on the app is therefore a bound method object, which is
+always truthy, so ``if not self.is_mounted: return`` never returns. The
+app-level guards need ``App.is_running`` to detect a stopped app.
+"""
+
+from __future__ import annotations
+
+import inspect
+from pathlib import Path
+from typing import cast
+
+from textual.app import App
+from textual.widget import Widget
+
+from strix.interface.tui import app as tui_app
+
+
+# App-level guards converted from the always-truthy self.is_mounted.
+_CONVERTED_GUARDS = 13
+
+
+class StoppedTuiState:
+    show_splash = False
+    is_running = False
+
+    def __init__(self) -> None:
+        self.query_count = 0
+
+    def is_mounted(self, _widget: object) -> bool:
+        return False
+
+    def query_one(self, *_args: object, **_kwargs: object) -> None:
+        self.query_count += 1
+        raise ValueError("the TUI is not mounted")
+
+
+def test_app_is_mounted_is_a_method_that_needs_a_widget() -> None:
+    """The API shape that caused the bug: truthy when read without calling it."""
+    assert inspect.isfunction(inspect.getattr_static(App, "is_mounted"))
+    assert "widget" in inspect.signature(App.is_mounted).parameters
+    assert bool(App().is_mounted) is True
+
+
+def test_widget_is_mounted_is_a_property() -> None:
+    """``Widget.is_mounted`` *is* a property — the source of the confusion."""
+    assert isinstance(inspect.getattr_static(Widget, "is_mounted"), property)
+
+
+def test_app_is_running_is_a_property() -> None:
+    assert isinstance(inspect.getattr_static(App, "is_running"), property)
+
+
+def test_tui_app_never_reads_is_mounted_off_itself() -> None:
+    """``self.is_mounted`` in the TUI is always a bug; widget access is fine."""
+    source = Path(str(tui_app.__file__)).read_text(encoding="utf-8")
+    offenders = [
+        f"{number}: {line.strip()}"
+        for number, line in enumerate(source.splitlines(), start=1)
+        if "self.is_mounted" in line
+    ]
+
+    assert not offenders, "self.is_mounted is always truthy; use self.is_running:\n" + "\n".join(
+        offenders
+    )
+    # A floor, not an exact count: new guards are welcome, silent removal is not.
+    assert source.count("self.is_running") >= _CONVERTED_GUARDS
+
+
+def test_real_tui_action_returns_before_query_when_app_is_stopped() -> None:
+    stopped_tui_state = StoppedTuiState()
+
+    tui_app.StrixTUIApp.action_toggle_help(cast("tui_app.StrixTUIApp", stopped_tui_state))
+
+    assert stopped_tui_state.query_count == 0