assistant: Insert creases for tool output (#17464)

This PR makes it so we insert creases for tool output.

Release Notes:

- N/A

crates/assistant/src/assistant_panel.rs

@@ -2198,6 +2198,47 @@ impl ContextEditor {
                     }
                 }
             }
+            ContextEvent::ToolFinished {
+                tool_use_id,
+                output_range,
+            } => {
+                self.editor.update(cx, |editor, cx| {
+                    let buffer = editor.buffer().read(cx).snapshot(cx);
+                    let (excerpt_id, _buffer_id, _) = buffer.as_singleton().unwrap();
+                    let excerpt_id = *excerpt_id;
+
+                    let placeholder = FoldPlaceholder {
+                        render: render_fold_icon_button(
+                            cx.view().downgrade(),
+                            IconName::PocketKnife,
+                            format!("Tool Result: {tool_use_id}").into(),
+                        ),
+                        constrain_width: false,
+                        merge_adjacent: false,
+                    };
+                    let render_trailer =
+                        move |_row, _unfold, _cx: &mut WindowContext| Empty.into_any();
+
+                    let start = buffer
+                        .anchor_in_excerpt(excerpt_id, output_range.start)
+                        .unwrap();
+                    let end = buffer
+                        .anchor_in_excerpt(excerpt_id, output_range.end)
+                        .unwrap();
+
+                    let buffer_row = MultiBufferRow(start.to_point(&buffer).row);
+
+                    let crease = Crease::new(
+                        start..end,
+                        placeholder,
+                        fold_toggle("tool-use"),
+                        render_trailer,
+                    );
+
+                    editor.insert_creases([crease], cx);
+                    editor.fold_at(&FoldAt { buffer_row }, cx);
+                });
+            }
             ContextEvent::Operation(_) => {}
             ContextEvent::ShowAssistError(error_message) => {
                 self.error_message = Some(error_message.clone());