Keep chat scrolling under user control

src/app/projects.rs

@@ -175,6 +175,7 @@ impl App {
         self.remember_project(project_id);
         self.selected_session = None;
         self.conversation.clear();
+        self.chat_follow_tail = true;
         self.context_notice = None;
         self.clear_a2ui();
         self.composer.clear();
@@ -189,6 +190,7 @@ impl App {
     pub(super) fn discard_session(&mut self, project_id: i32) {
         if self.drafts.remove(&project_id).is_some() && self.draft_selected(project_id) {
             self.conversation.clear();
+            self.chat_follow_tail = true;
             self.context_notice = None;
             self.clear_a2ui();
             self.composer.clear();

src/app/view/chat.rs

@@ -315,9 +315,14 @@ impl App {
                     .style(preference_group_style),
                 );
             }
-            let transcript = scrollable(messages)
-                .id(chat_scroll_id())
-                .height(Length::Fill);
+            let transcript = if self.chat_follow_tail {
+                scrollable(messages).anchor_bottom()
+            } else {
+                scrollable(messages)
+            }
+            .id(chat_scroll_id())
+            .on_scroll(Message::ChatScrolled)
+            .height(Length::Fill);
             let conversation = column![
                 transcript,
                 container(composer_content,)