UX: opens side panel early to avoid jitter (#21516)

Hard to write a test for this behavior, this is a micro optimisation which doesn’t change the behavior but only makes it smoother by happening right before async request.

plugins/chat/assets/javascripts/discourse/routes/chat-channel-thread.js

@@ -59,5 +59,7 @@ export default class ChatChannelThread extends DiscourseRoute {
         return;
       }
     }
+
+    this.chatStateManager.openSidePanel();
   }
 }

plugins/chat/assets/javascripts/discourse/routes/chat-channel-threads.js

@@ -1,9 +1,11 @@
 import DiscourseRoute from "discourse/routes/discourse";
 import { inject as service } from "@ember/service";
 import { action } from "@ember/object";
+
 export default class ChatChannelThreads extends DiscourseRoute {
   @service router;
   @service chatChannelThreadListPane;
+  @service chatStateManager;
 
   beforeModel(transition) {
     const channel = this.modelFor("chat.channel");
@@ -13,11 +15,15 @@ export default class ChatChannelThreads extends DiscourseRoute {
       this.router.transitionTo("chat.channel", ...channel.routeModels);
       return;
     }
+
+    this.chatStateManager.openSidePanel();
   }
 
   @action
-  willTransition() {
-    this.chatChannelThreadListPane.close();
+  willTransition(transition) {
+    if (transition.targetName !== "chat.channel.thread") {
+      this.chatChannelThreadListPane.close();
+    }
   }
 
   activate() {