fix: _refresh_hierarchy tolerates an empty screen stack (#147)

src/korvid/ui/app.py

@@ -31,7 +31,7 @@
 
 import yaml
 from rich.text import Text
-from textual.app import App, ComposeResult, SuspendNotSupported
+from textual.app import App, ComposeResult, ScreenStackError, SuspendNotSupported
 from textual.binding import Binding
 from textual.containers import Horizontal
 from textual.coordinate import Coordinate
@@ -2387,7 +2387,13 @@ def lookup(view: str, namespace: str) -> list[Summary] | None:
     def _refresh_hierarchy(self) -> None:
         """Rebuild an open hierarchy tree from the current store state."""
         ctx = self._hierarchy_ctx
-        screen = self.screen
+        try:
+            screen = self.screen
+        except ScreenStackError:
+            # A ResourcesUpdated dispatched during app teardown can land
+            # after the screen stack is emptied (flaky-CI issue #147):
+            # no screen simply means no tree to refresh.
+            return
         if ctx is None or not isinstance(screen, HierarchyScreen):
             return
         title, refs, namespace, scope = ctx

tests/ui/test_hierarchy_nav.py

@@ -4,6 +4,9 @@
 import asyncio
 from collections.abc import AsyncIterator
 from typing import Any
+from unittest import mock
+
+from textual.app import ScreenStackError
 
 from korvid.core.config import KorvidConfig
 from korvid.core.store import ALL_NAMESPACES, ResourceStore, Summary
@@ -424,6 +427,24 @@ async def navigate_then_switch(*args: object, **kwargs: object) -> None:
             app._ctx_switching = False
 
 
+async def test_refresh_hierarchy_survives_an_empty_screen_stack() -> None:
+    """A ResourcesUpdated dispatched during app teardown reaches
+    _refresh_hierarchy after the screen stack is emptied: reading
+    App.screen then raises ScreenStackError and fails the whole run
+    (flaky-CI issue #147) - the refresh must treat 'no screen' as
+    'no tree open'."""
+    app, _ = make_app(_HELM_DATA, components=_WEB_COMPONENTS)
+    async with app.run_test() as pilot:
+        await pilot.pause(0.1)
+        # Simulate the teardown interleaving deterministically: the message
+        # handler runs while the screen stack is already empty.
+        with mock.patch.object(
+            type(app), "screen", property(mock.Mock(side_effect=ScreenStackError))
+        ):
+            app._refresh_hierarchy()  # must not raise
+        assert True  # reaching here is the assertion: no ScreenStackError
+
+
 async def test_describe_from_tree_node() -> None:
     app, describe_calls = make_app(_HELM_DATA, components=_WEB_COMPONENTS)
     async with app.run_test() as pilot: