wrap markdown at render time (#4506)

This results in correctly indenting list items with long lines.

<img width="1006" height="251" alt="Screenshot 2025-09-30 at 10 00
48 AM"
src="https://github.com/user-attachments/assets/0a076cf6-ca3c-4efb-b3af-dc07617cdb6f"
/>

codex-rs/tui/src/chatwidget.rs

@@ -256,6 +256,8 @@ pub(crate) struct ChatWidget {
     ghost_snapshots_disabled: bool,
     // Whether to add a final message separator after the last message
     needs_final_message_separator: bool,
+
+    last_rendered_width: std::cell::Cell<Option<usize>>,
 }
 
 struct UserMessage {
@@ -658,7 +660,10 @@ impl ChatWidget {
                 self.add_to_history(history_cell::FinalMessageSeparator::new(elapsed_seconds));
                 self.needs_final_message_separator = false;
             }
-            self.stream_controller = Some(StreamController::new(self.config.clone()));
+            self.stream_controller = Some(StreamController::new(
+                self.config.clone(),
+                self.last_rendered_width.get().map(|w| w.saturating_sub(2)),
+            ));
         }
         if let Some(controller) = self.stream_controller.as_mut()
             && controller.push(&delta)
@@ -912,6 +917,7 @@ impl ChatWidget {
             ghost_snapshots: Vec::new(),
             ghost_snapshots_disabled: true,
             needs_final_message_separator: false,
+            last_rendered_width: std::cell::Cell::new(None),
         }
     }
 
@@ -974,6 +980,7 @@ impl ChatWidget {
             ghost_snapshots: Vec::new(),
             ghost_snapshots_disabled: true,
             needs_final_message_separator: false,
+            last_rendered_width: std::cell::Cell::new(None),
         }
     }
 
@@ -1447,7 +1454,7 @@ impl ChatWidget {
                 } else {
                     // Show explanation when there are no structured findings.
                     let mut rendered: Vec<ratatui::text::Line<'static>> = vec!["".into()];
-                    append_markdown(&explanation, &mut rendered, &self.config);
+                    append_markdown(&explanation, None, &mut rendered, &self.config);
                     let body_cell = AgentMessageCell::new(rendered, false);
                     self.app_event_tx
                         .send(AppEvent::InsertHistoryCell(Box::new(body_cell)));
@@ -1456,7 +1463,7 @@ impl ChatWidget {
                 let message_text =
                     codex_core::review_format::format_review_findings_block(&output.findings, None);
                 let mut message_lines: Vec<ratatui::text::Line<'static>> = Vec::new();
-                append_markdown(&message_text, &mut message_lines, &self.config);
+                append_markdown(&message_text, None, &mut message_lines, &self.config);
                 let body_cell = AgentMessageCell::new(message_lines, true);
                 self.app_event_tx
                     .send(AppEvent::InsertHistoryCell(Box::new(body_cell)));
@@ -1998,6 +2005,7 @@ impl WidgetRef for &ChatWidget {
                 tool.render_ref(area, buf);
             }
         }
+        self.last_rendered_width.set(Some(area.width as usize));
     }
 }