FIX: Sidebar mode switching on subfolder (#27026)

app/assets/javascripts/discourse/app/components/sidebar/switch-panel-buttons.gjs

@@ -4,43 +4,32 @@ import { fn } from "@ember/helper";
 import { action } from "@ember/object";
 import { service } from "@ember/service";
 import DButton from "discourse/components/d-button";
-import { defaultHomepage } from "discourse/lib/utilities";
-import getURL from "discourse-common/lib/get-url";
 
 export default class SwitchPanelButtons extends Component {
   @service router;
   @service sidebarState;
 
-  @tracked currentPanel;
   @tracked isSwitching = false;
 
-  get destination() {
-    if (this.currentPanel) {
-      const url =
-        this.currentPanel.switchButtonDefaultUrl ||
-        this.currentPanel.lastKnownURL;
-      return url === "/" ? `discovery.${defaultHomepage()}` : getURL(url);
-    }
-    return null;
-  }
-
   @action
   async switchPanel(panel) {
     this.isSwitching = true;
-    this.currentPanel = panel;
     this.sidebarState.currentPanel.lastKnownURL = this.router.currentURL;
 
-    if (this.destination) {
-      try {
-        await this.router.transitionTo(this.destination).followRedirects();
-        this.sidebarState.setPanel(this.currentPanel.key);
-      } catch (e) {
-        if (e.name !== "TransitionAborted") {
-          throw e;
-        }
-      } finally {
-        this.isSwitching = false;
+    const destination = panel?.switchButtonDefaultUrl || panel?.lastKnownURL;
+    if (!destination) {
+      return;
+    }
+
+    try {
+      await this.router.transitionTo(destination).followRedirects();
+      this.sidebarState.setPanel(panel.key);
+    } catch (e) {
+      if (e.name !== "TransitionAborted") {
+        throw e;
       }
+    } finally {
+      this.isSwitching = false;
     }
   }