Contouring: close the discard dialog on Yes; live erase boundary

(1) The "Discard unsaved edits?" confirm did not dismiss on Yes: self.close()
    ran synchronously inside the message box's button-click handler, deleting
    the box (a child of the panel) before it dismissed. Defer the panel close
    with QTimer.singleShot.
(2) Erasing left the old boundary on screen until the drag ended. The full
    render drew the working-mask overlay (and the edited structure's committed
    contour) statically, and _live_update_axial stacked a live overlay on top.
    Now skip the edited structure's committed contour, and hand the axial
    working overlay to the live updater so each brush/erase step removes and
    redraws it - the dashed boundary shrinks in real time while erasing.

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

Author: adityaapte

cerr/viewer/pycerr_gui.py

@@ -2608,7 +2608,12 @@ def refresh_views(self, only=None):
                           aspect="equal")
 
             # ---- structure contours ----
+            ctl = self.contourCtl
+            editStrNum = (ctl.structNum if ctl is not None and ctl.isVisible()
+                          else None)
             for strNum in self._axis_structs(orient):
+                if strNum == editStrNum:
+                    continue   # being edited: shown via the live overlay below
                 mask = self._struct_mask(strNum)
                 if mask is None or mask.shape != self.scan3M.shape:
                     continue
@@ -2623,18 +2628,24 @@ def refresh_views(self, only=None):
                     self._draw_contour_dots(ax, cs, color)
 
             # ---- live contouring overlay (working mask being edited) ----
-            ctl = self.contourCtl
             if ctl is not None and ctl.isVisible() and ctl.mask3M is not None \
                     and ctl.mask3M.shape == self.scan3M.shape:
                 cslc = slicer(ctl.mask3M)
+                im = cs = None
                 if np.any(cslc):
-                    ax.imshow(np.ma.masked_where(~cslc, cslc.astype(float)),
-                              cmap=ListedColormap([ctl.color]), extent=extent,
-                              alpha=0.35, vmin=0, vmax=1,
-                              interpolation="nearest", aspect="equal")
-                    ax.contour(hV, vV, cslc.astype(float), levels=[0.5],
-                               colors=[ctl.color], linewidths=1.6,
-                               linestyles="--")
+                    im = ax.imshow(
+                        np.ma.masked_where(~cslc, cslc.astype(float)),
+                        cmap=ListedColormap([ctl.color]), extent=extent,
+                        alpha=0.35, vmin=0, vmax=1,
+                        interpolation="nearest", aspect="equal")
+                    cs = ax.contour(hV, vV, cslc.astype(float), levels=[0.5],
+                                    colors=[ctl.color], linewidths=1.6,
+                                    linestyles="--")
+                if view is ctl.axView:
+                    # the live updater owns the axial overlay, so each brush
+                    # step removes and redraws it (no stale boundary on erase)
+                    ctl._liveIm = im
+                    ctl._liveContour = cs
 
             # ---- registration QA split/lens guides ----
             if regComp is not None:
@@ -3890,7 +3901,10 @@ def closeEvent(self, event):
             def _on_done(btn):
                 if box.standardButton(btn) == QtWidgets.QMessageBox.Yes:
                     self._force_close = True
-                    self.close()
+                    # defer: let the message box finish closing itself first,
+                    # then close the panel (closing it now, mid button-click,
+                    # deletes the box before it dismisses).
+                    QtCore.QTimer.singleShot(0, self.close)
             box.buttonClicked.connect(_on_done)
             box.show()
             box.raise_()