FIX: correctly closes panels in threads (#31013)

The following case was bugged:

- visit a thread in full page chat
- click channel title
- click back button in channel navbar
- 💥 you would have a channel with limited width as if there was
still the thread showing next to it, but it was empty

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

@@ -6,7 +6,6 @@ export default class ChatChannelThread extends DiscourseRoute {
   @service router;
   @service chatStateManager;
   @service chat;
-  @service chatThreadPane;
 
   redirectToChannel(channel, transition) {
     transition.abort();
@@ -36,15 +35,14 @@ export default class ChatChannelThread extends DiscourseRoute {
   }
 
   @action
-  willTransition(transition) {
+  activate() {
-    if (
+    this.chat.activeMessage = null;
-      transition.targetName === "chat.channel.index" ||
+    this.chatStateManager.openSidePanel();
-      transition.targetName === "chat.channel.near-message" ||
-      transition.targetName === "chat.index" ||
-      !transition.targetName.startsWith("chat")
-    ) {
-      this.chatStateManager.closeSidePanel();
   }
+
+  @action
+  deactivate() {
+    this.chatStateManager.closeSidePanel();
   }
 
   beforeModel() {
@@ -55,7 +53,5 @@ export default class ChatChannelThread extends DiscourseRoute {
     ) {
       this.controllerFor("chat-channel-thread").set("targetMessageId", null);
     }
-
-    this.chatStateManager.openSidePanel();
   }
 }

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

@@ -16,24 +16,16 @@ export default class ChatChannelThreads extends DiscourseRoute {
       this.router.transitionTo("chat.channel", ...channel.routeModels);
       return;
     }
-
-    this.chatStateManager.openSidePanel();
   }
 
   @action
   activate() {
     this.chat.activeMessage = null;
+    this.chatStateManager.openSidePanel();
   }
 
   @action
-  willTransition(transition) {
+  deactivate() {
-    if (
-      transition.targetName === "chat.channel.index" ||
-      transition.targetName === "chat.channel.near-message" ||
-      transition.targetName === "chat.index" ||
-      !transition.targetName.startsWith("chat")
-    ) {
     this.chatStateManager.closeSidePanel();
   }
-  }
 }

plugins/chat/spec/system/navigation_spec.rb

@@ -139,6 +139,24 @@ RSpec.describe "Navigation", type: :system do
     end
   end
 
+  context "when opening channel settings from thread" do
+    fab!(:thread) { Fabricate(:chat_thread, channel: category_channel, use_service: true) }
+
+    before do
+      category_channel.update!(threading_enabled: true)
+      Fabricate(:chat_message, thread: thread, use_service: true)
+      thread.add(current_user)
+    end
+
+    it "correctly closes the side panel" do
+      chat_page.visit_thread(thread)
+
+      find(".c-navbar__channel-title").click
+
+      expect(page).to have_no_selector(".main-chat-outlet.has-side-panel-expanded")
+    end
+  end
+
   context "when collapsing full page with no previous state" do
     it "redirects to home page" do
       chat_page.open