fix(multiuser): properly clear fake cursors (#3845)

zellij-server/src/panes/terminal_pane.rs

@@ -806,6 +806,20 @@ impl Pane for TerminalPane {
         self.style.rounded_corners = rounded_corners;
         self.frame.clear();
     }
+    fn drain_fake_cursors(&mut self) -> Option<HashSet<(usize, usize)>> {
+        if !self.fake_cursor_locations.is_empty() {
+            for (y, _x) in &self.fake_cursor_locations {
+                // we do this because once these fake_cursor_locations
+                // have been drained, we have to make sure to render the line
+                // they appeared on so that whatever clears their location
+                // won't leave a hole
+                self.grid.update_line_for_rendering(*y);
+            }
+            Some(self.fake_cursor_locations.drain().collect())
+        } else {
+            None
+        }
+    }
 }
 
 impl TerminalPane {

zellij-server/src/tab/mod.rs

@@ -500,6 +500,9 @@ pub trait Pane {
     fn query_should_be_suppressed(&self) -> bool {
         false
     }
+    fn drain_fake_cursors(&mut self) -> Option<HashSet<(usize, usize)>> {
+        None
+    }
 }
 
 #[derive(Clone, Debug)]

zellij-server/src/ui/pane_contents_and_ui.rs

@@ -57,6 +57,10 @@ impl<'a> PaneContentsAndUi<'a> {
     ) -> Result<()> {
         let err_context = "failed to render pane contents to multiple clients";
 
+        // here we drop the fake cursors so that their lines will be updated
+        // and we can clear them from the UI below
+        drop(self.pane.drain_fake_cursors());
+
         if let Some((character_chunks, raw_vte_output, sixel_image_chunks)) =
             self.pane.render(None).context(err_context)?
         {