feat: enhance split pane focus UI and fix graceful exit tab cleanup

- Implement 4-sided inner absolute border for active pane focus

- Fix 'exit' gracefully closing tabs not removing empty tab groups

- Sync system monitoring automatically on active group switches

src/app/mod.rs

@@ -639,45 +639,7 @@ impl Ashell {
                         || reason == "ssh session closed";
                     // Auto-close the pane on graceful exit (e.g. user typed exit)
                     if is_graceful_exit {
-                        if let Some(ix) = self.tabs.iter().position(|t| t.id == tab_id) {
-                            self.tabs[ix].backend.send(BackendCommand::Close);
-                            self.tabs.remove(ix);
-                        }
-                        if let Some(g) = self.tab_groups.iter_mut().find(|g| g.pane_root.contains(&tab_id)) {
-                            g.pane_root.remove_tab(&tab_id);
-                        }
-                        self.pane_root.remove_tab(&tab_id);
-                        self.sync_pane_root_to_group();
-                        if self.tabs.is_empty() || self.tab_groups.is_empty() {
-                            self.pane_root = PaneLayout::Single(String::new());
-                            self.focused_pane_path = vec![];
-                            self.active_tab = None;
-                            self.active_group = None;
-                            self.tab_groups.clear();
-                            self.tabs.clear();
-                            self.system_tab_id = None;
-                            self.cpu_history.clear();
-                            self.net_rx_history.clear();
-                            self.net_tx_history.clear();
-                            self.system_status = None;
-                            if let Some(handle) = self.sftp_handles.remove(&tab_id) {
-                                handle.close();
-                            }
-                            return changed;
-                        }
-
-                        let was_active = self.active_tab.as_deref() == Some(tab_id.as_str());
-                        if was_active
-                            || self.active_tab.as_ref().is_some_and(|active_id| !self.tabs.iter().any(|tab| &tab.id == active_id))
-                        {
-                            let first_id = self.pane_root.tab_ids().first().copied().map(String::from)
-                                .or_else(|| self.tabs.first().map(|t| t.id.clone()));
-                            if let Some(new_id) = first_id {
-                                self.active_tab = Some(new_id.clone());
-                                self.focus_pane_with_id(new_id);
-                            }
-                        }
-                        self.sync_system_tab_to_active_group();
+                        self.handle_tab_close(tab_id.clone());
                         self.status = reason.into();
                         self.remote_sample_in_flight = false;
                         return changed;

src/app/ui.rs

@@ -1639,23 +1639,31 @@ impl Ashell {
                         }
                     })
                     .unwrap_or(cx.theme().success);
-                if is_focused {
-                    el = h_flex()
-                        .size_full()
-                        .child(
-                            div()
-                                .w(px(2.))
-                                .h_full()
-                                .flex_none()
-                                .bg(indicator_color),
-                        )
-                        .child(el.flex_1().min_w(px(0.)));
-                } else {
-                    el = h_flex()
-                        .size_full()
-                        .child(div().w(px(2.)).h_full().flex_none())
-                        .child(el.opacity(0.85).flex_1().min_w(px(0.)));
+                let has_multiple_panes = this.pane_root.tab_ids().len() > 1;
+
+                if !is_focused {
+                    el = el.opacity(0.85);
                 }
+
+                if has_multiple_panes {
+                    if is_focused {
+                        el = div()
+                            .size_full()
+                            .relative()
+                            .child(div().absolute().top(px(1.)).left(px(1.)).right(px(1.)).h(px(1.)).bg(indicator_color))
+                            .child(div().absolute().bottom(px(1.)).left(px(1.)).right(px(1.)).h(px(1.)).bg(indicator_color))
+                            .child(div().absolute().left(px(1.)).top(px(1.)).bottom(px(1.)).w(px(1.)).bg(indicator_color))
+                            .child(div().absolute().right(px(1.)).top(px(1.)).bottom(px(1.)).w(px(1.)).bg(indicator_color))
+                            .p(px(4.))
+                            .child(el);
+                    } else {
+                        el = div()
+                            .size_full()
+                            .p(px(4.))
+                            .child(el);
+                    }
+                }
+
                 el.into_any_element()
             }
             PaneLayout::Horizontal(children, ratio) => {

src/session/mod.rs

@@ -488,15 +488,19 @@ impl Ashell {
     }
 
     pub(crate) fn close_tab(&mut self, id: String, cx: &mut Context<Self>) {
+        self.handle_tab_close(id);
+        cx.notify();
+    }
+
+    pub(crate) fn handle_tab_close(&mut self, id: String) {
         let group_ix = self.tab_groups.iter().position(|g| g.pane_root.contains(&id));
         let Some(ref group) = group_ix.map(|i| self.tab_groups[i].clone()) else {
             // Fallback: find and close individual tab
-            eprintln!("[close_tab] no group found for tab '{}', closing individually", id);
+            eprintln!("[handle_tab_close] no group found for tab '{}', closing individually", id);
             if let Some(ix) = self.tabs.iter().position(|tab| tab.id == id) {
                 self.tabs[ix].backend.send(BackendCommand::Close);
                 self.tabs.remove(ix);
             }
-            cx.notify();
             return;
         };
 
@@ -504,7 +508,7 @@ impl Ashell {
         let pane_ids_str: Vec<&str> = pane_ids.iter().map(|s| *s).collect();
         let is_group_close = pane_ids.len() <= 1;
         eprintln!(
-            "[close_tab] id='{}' group_panes={:?} is_group_close={}",
+            "[handle_tab_close] id='{}' group_panes={:?} is_group_close={}",
             id, pane_ids_str, is_group_close
         );
 
@@ -573,7 +577,6 @@ impl Ashell {
             for (_, handle) in self.sftp_handles.drain() {
                 handle.close();
             }
-            cx.notify();
             return;
         }
 
@@ -606,7 +609,6 @@ impl Ashell {
             }
         }
         self.sync_system_tab_to_active_group();
-        cx.notify();
     }
 
     pub(crate) fn focus_terminal(