fix(gui): clear stale result on successful run, not on mode switch (F10 vs #70)

The first F10 pass cleared the previous mode's result inside _on_mode_change, but
that defeated release-gate contract #70
(test_run_validation_error_preserves_previous_valid_result_overview): switching
mode then hitting a validation error left "No results" because the result was
already wiped at switch time, so there was nothing to preserve.

Reconcile by moving the clear off the switch: a successful run in the new mode
replaces the result (so stale wrong-mode output is never shown/exported once you
actually compute — F10's real intent, satisfied via the _on_calc_finished ->
_show_*_results path), while a failed or validation-errored run returns early and
keeps the last good result (#70). Rewrite F10's own test to assert the new
timing (switch preserves; a successful run replaces).

Both previously-conflicting tests pass; 221 neighborhood tests pass; ruff clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: Aaronhaohao

app_desktop/window.py

@@ -2180,16 +2180,12 @@ def _update_theme_from_palette(self, *args):
 
     def _on_mode_change(self):
         mode = self.mode_combo.currentData()
-        # Clear the previous mode's result text / CSV / plot so a mode switch
-        # never shows (or exports) another mode's stale output (audit F10). Skip
-        # while restoring a workspace (the just-restored result must survive) or
-        # while a worker is running (don't wipe an in-flight run's state).
-        if (
-            not getattr(self, "_workspace_restoring", False)
-            and not self._has_running_worker()
-            and hasattr(self, "_reset_csv_data")
-        ):
-            self._reset_csv_data(clear_non_tabular_result=True)
+        # Note: the previous mode's result is deliberately NOT cleared here.
+        # A successful run in the new mode replaces it (so stale wrong-mode
+        # output is never shown/exported once you actually compute — audit F10),
+        # while a failed or validation-errored run preserves the last good
+        # result (release-gate contract #70). Clearing at switch time would
+        # defeat that preserve-on-failure contract.
         self._sync_manual_table_columns_for_mode(mode)
         mode_indices = {
             "extrapolation": 0,

tests/test_desktop_mode_stack.py

@@ -33,17 +33,26 @@ def _set_combo_data(combo: Any, value: str) -> None:
     QApplication.processEvents()
 
 
-def test_mode_switch_clears_previous_mode_result(window: Any) -> None:
-    """Switching modes must clear the previous mode's result text and CSV export
-    buffer so stale wrong-mode data is never shown or exported (audit F10)."""
+def test_mode_switch_preserves_result_until_a_successful_run_replaces_it(window: Any) -> None:
+    """A mode switch must NOT wipe the previous result: a successful run in the
+    new mode replaces it (so stale wrong-mode output is never shown/exported once
+    you actually compute — audit F10), while a failed/validation-errored run
+    keeps the last good result (release-gate contract #70). Clearing at switch
+    time would defeat that preserve-on-failure contract."""
     window._set_csv_data([{"x": "1", "y": "2"}], ["x", "y"])
-    window.result_edit.setPlainText("stale fit result from a previous mode")
+    window.result_edit.setPlainText("prior-mode result")
     assert window._csv_rows
 
+    # Switching mode alone preserves the prior result (nothing has recomputed).
     _set_combo_data(window.mode_combo, "statistics")
-
-    assert window._csv_rows == []
-    assert window.result_edit.toPlainText() == ""
+    assert window._csv_rows == [{"x": "1", "y": "2"}]
+    assert window.result_edit.toPlainText() == "prior-mode result"
+
+    # A successful run in the new mode replaces the result with fresh output.
+    window._set_csv_data([{"stat": "mean", "value": "3"}], ["stat", "value"])
+    window._set_result_text("statistics result", final_result=True)
+    assert window._csv_rows == [{"stat": "mean", "value": "3"}]
+    assert "statistics result" in window.result_edit.toPlainText()
 
 
 def _measure_mode_stack_width(window: Any) -> int: