From f25d2a585ab68809bc7a2a9494dd7c04b64716b0 Mon Sep 17 00:00:00 2001
From: Alessandro Genova <alessandro.genova@kitware.com>
Date: Mon, 29 Jun 2026 11:37:58 -0400
Subject: [PATCH 1/2] fix crash from VolumeData unregistering its color-map
 proxy on the worker thread

---
 tomviz/pipeline/data/VolumeData.cxx | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/tomviz/pipeline/data/VolumeData.cxx b/tomviz/pipeline/data/VolumeData.cxx
index 714faafa7..a3ad0c9e1 100644
--- a/tomviz/pipeline/data/VolumeData.cxx
+++ b/tomviz/pipeline/data/VolumeData.cxx
@@ -24,7 +24,10 @@
 #include <vtkSMTransferFunctionManager.h>
 #include <vtkSMTransferFunctionProxy.h>
 
+#include <QCoreApplication>
 #include <QJsonArray>
+#include <QMetaObject>
+#include <QThread>
 
 #include <array>
 
@@ -70,9 +73,31 @@ VolumeData::~VolumeData()
   // unique, counter-based name. The proxy manager holds its own reference,
   // so dropping our vtkSmartPointer isn't enough — without this unregister
   // the proxy lives until app exit and every load/reset cycle adds another.
-  if (m_colorMap) {
+  if (!m_colorMap) {
+    return;
+  }
+
+  // UnRegisterProxy mutates the ParaView session proxy manager, which is
+  // not thread-safe and must run on the GUI thread. A VolumeData is a port
+  // payload whose lifetime is governed by shared_ptr refcounting, and the
+  // pipeline executor can drop the last ref on the worker thread (inflight
+  // eviction, clearHandle, the OnDisk deleter) — destroying us there.
+  // Touching the proxy manager off the GUI thread races
+  // pqServerManagerObserver / pqServerManagerModel and crashes in
+  // onProxyRegistered. Marshal the unregister to the GUI thread; the proxy
+  // manager's own reference keeps the captured proxy alive until the queued
+  // call runs.
+  vtkSmartPointer<vtkSMProxy> proxy = m_colorMap;
+  auto unregister = [proxy]() {
     vtkNew<vtkSMParaViewPipelineController> controller;
-    controller->UnRegisterProxy(m_colorMap);
+    controller->UnRegisterProxy(proxy);
+  };
+
+  auto* app = QCoreApplication::instance();
+  if (!app || QThread::currentThread() == app->thread()) {
+    unregister();
+  } else {
+    QMetaObject::invokeMethod(app, unregister, Qt::QueuedConnection);
   }
 }
 

From 1ee518a0f545841b0aa51fdd8dbf2c73635eed43 Mon Sep 17 00:00:00 2001
From: Alessandro Genova <alessandro.genova@kitware.com>
Date: Mon, 29 Jun 2026 12:18:18 -0400
Subject: [PATCH 2/2] keep downstream visualization on screen while inserting
 an operator

---
 tomviz/TransformUtils.cxx | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tomviz/TransformUtils.cxx b/tomviz/TransformUtils.cxx
index 0e3359daa..60f205dd7 100644
--- a/tomviz/TransformUtils.cxx
+++ b/tomviz/TransformUtils.cxx
@@ -168,6 +168,15 @@ static pipeline::DeferredLinkInfo appendTransformAtPortDeferred(
     deferred.linksToRestore.append({ targetPort, sinkInput });
     pip->removeLink(m.link);
     pip->createLink(m.newOut, sinkInput);
+    // removeLink() reset this terminal sink/group's visualization. Re-show it
+    // (the VTK objects still hold the last data) so the downstream module
+    // stays on screen while the dialog is open. Nothing clears it again until
+    // the not-yet-run transform produces output and the sink swaps it in
+    // directly, so it also stays visible all through execution. Mirrors the
+    // restorePresentation() the dialog's cancel path performs.
+    if (auto* node = sinkInput->node()) {
+      node->restorePresentation();
+    }
   }
   return deferred;
 }