fix: guard tree rendering against destroyed window actors

If a window gets destroyed mid-render (app crash, rapid close, async
cleanup), nodes in the tree still reference the finalized GObject.
Accessing anything on it segfaults gnome-shell (signal 11).
Adds isNodeValid() that probes the actor with get_name() in a try/catch
(GJS throws on finalized GObjects rather than segfaulting). Filters dead
nodes out before layout, and guards the remaining property accesses that
can race with window destruction.

Author: braceyourself

lib/extension/tree.js

@@ -459,7 +459,9 @@ export class Node extends GObject.Object {
 style_class: "window-tabbed-tab",
 x_expand: true,
 });
+// Window tracker may not resolve an app for a dying window
 letapp=this.app;
+if(!app)return;
 letlabelText=this._getTitle();
 letmetaWin=this.nodeValue;
 lettitleButton=newSt.Button({
@@ -537,6 +539,21 @@ export class Node extends GObject.Object {
 returnnull;
 }
 
+// Check if the underlying window actor is still alive. GJS throws
+// on property access of finalized GObjects rather than segfaulting,
+// so a cheap get_name() call is enough to detect dead actors.
+isNodeValid(){
+if(!this.isWindow())returntrue;
+try{
+letactor=this._actor;
+if(!actor)returnfalse;
+actor.get_name();
+returntrue;
+}catch(e){
+returnfalse;
+}
+}
+
 render(){
 // Always update the title for the tab
 if(this.tab!==null&&this.tab!==undefined){
@@ -1274,8 +1291,12 @@ export class Tree extends Node {
 tiledChildren.forEach((w)=>{
 if(w.renderRect){
 if(w.renderRect.width>0&&w.renderRect.height>0){
+// Window may have been destroyed since processNode computed renderRect
 letmetaWin=w.nodeValue;
-this.extWm.move(metaWin,w.renderRect);
+try{
+this.extWm.move(metaWin,w.renderRect);
+}catch(e){
+}
 }else{
 Logger.debug(`ignoring apply for ${w.renderRect.width}x${w.renderRect.height}`);
 }
@@ -1385,7 +1406,8 @@ export class Tree extends Node {
 });
 }
 
-tiledChildren.forEach((child,index)=>{
+// Skip windows whose actors were destroyed mid-render
+tiledChildren.filter((c)=>c.isNodeValid()).forEach((child,index)=>{
 // A monitor can contain a window or container child
 if(node.layout===LAYOUT_TYPES.HSPLIT||node.layout===LAYOUT_TYPES.VSPLIT){
 this.processSplit(node,child,params,index);
@@ -1527,10 +1549,17 @@ export class Tree extends Node {
 if(node.childNodes.length>1||alwaysShowDecorationTab){
 nodeY=nodeRect.y+params.stackedHeight;
 nodeHeight=nodeRect.height-params.stackedHeight;
-if(node.decoration&&child.isWindow()){
+if(node.decoration&&child.isWindow()&&child.isNodeValid()){
 letgap=this.extWm.calculateGaps(node);
 letrenderRect=this.processGap(node);
-letborderWidth=child.actor.border.get_theme_node().get_border_width(St.Side.TOP);
+// Border actor may be gone if the window was destroyed mid-render
+letborderWidth=0;
+try{
+if(child.actor?.border){
+borderWidth=child.actor.border.get_theme_node().get_border_width(St.Side.TOP);
+}
+}catch(e){
+}
 
 // Make adjustments to the gaps
 letadjust=4*Utils.dpi();
@@ -1552,7 +1581,12 @@ export class Tree extends Node {
 }else{
 decoration.hide();
 }
-if(!decoration.contains(child.tab))decoration.add_child(child.tab);
+if(child.tab&&!decoration.contains(child.tab)){
+try{
+decoration.add_child(child.tab);
+}catch(e){
+}
+}
 }
 
 child.render();