test(tui): cover after-render update-notice snapshot cleanup

Extract the after_render frame-clear closure into a named
_clear_prompt_frame_snapshot method so the lifecycle cleanup is directly
testable, and assert a completed frame leaves _prompt_frame_update_notice
as None.

Author: elkaix

src/pythinker_code/ui/shell/prompt.py

@@ -2842,14 +2842,8 @@ def _capture_prompt_frame(app: Application[str]) -> None:
                 terminal_rows=size.rows,
             )
 
-        def _clear_prompt_frame(_app: Application[str]) -> None:
-            self._current_prompt_frame = None
-            # Drop the per-frame notice snapshot with the frame so a later render
-            # can never read a value captured for a stale frame/mode.
-            self._prompt_frame_update_notice = None
-
         self._session.app.before_render.add_handler(_capture_prompt_frame)
-        self._session.app.after_render.add_handler(_clear_prompt_frame)
+        self._session.app.after_render.add_handler(self._clear_prompt_frame_snapshot)
 
         # Throttle redraws so the fast streaming-reveal cadence can't overwhelm
         # slower terminals (best practice for "invalidate is called a lot").
@@ -3278,6 +3272,13 @@ def _make_prompt_frame_collector(self) -> PromptFrameCollector:
             turn_is_starting=lambda: getattr(self, "_turn_starting", False),
         )
 
+    def _clear_prompt_frame_snapshot(self, _app: Application[str] | None = None) -> None:
+        """after_render handler: drop the captured frame and its per-frame update
+        notice together, so a later render can never read a snapshot captured for a
+        stale frame/mode."""
+        self._current_prompt_frame = None
+        self._prompt_frame_update_notice = None
+
     def _prompt_frame_for_render(self, *, columns: int | None = None) -> PromptFrame:
         current = getattr(self, "_current_prompt_frame", None)
         if current is not None:

tests/ui_and_conv/test_prompt_height_budget.py

@@ -179,6 +179,14 @@ def test_shell_render_refreshes_update_notice_snapshot(
     session._append_update_notice(fragments, 80)
     assert fragments == []
 
+    # The registered after_render cleanup drops the snapshot with the frame, so a
+    # completed frame never leaves a value for the next render to read.
+    session._current_prompt_frame = object()  # type: ignore[assignment]
+    session._prompt_frame_update_notice = "↑ Update available"
+    session._clear_prompt_frame_snapshot()
+    assert session._current_prompt_frame is None
+    assert session._prompt_frame_update_notice is None
+
 
 def test_two_row_modal_uses_hint_then_tail(monkeypatch: pytest.MonkeyPatch) -> None:
     session = _session_for_scene(