fix terminal corruption that could happen when onboarding and update banner (#5269)

Instead of printing characters before booting the app, make the upgrade
banner a history cell so it's well-behaved.

<img width="771" height="586" alt="Screenshot 2025-10-16 at 4 20 51 PM"
src="https://github.com/user-attachments/assets/90629d47-2c3d-4970-a826-283795ab34e5"
/>

---------

Co-authored-by: Josh McKinney <joshka@openai.com>

codex-rs/tui/src/history_cell.rs

@@ -15,6 +15,8 @@ use crate::style::user_message_style;
 use crate::text_formatting::format_and_truncate_tool_result;
 use crate::text_formatting::truncate_text;
 use crate::ui_consts::LIVE_PREFIX_COLS;
+use crate::updates::UpdateAction;
+use crate::version::CODEX_CLI_VERSION;
 use crate::wrapping::RtOptions;
 use crate::wrapping::word_wrap_line;
 use crate::wrapping::word_wrap_lines;
@@ -264,6 +266,60 @@ impl HistoryCell for PlainHistoryCell {
     }
 }
 
+#[cfg_attr(debug_assertions, allow(dead_code))]
+#[derive(Debug)]
+pub(crate) struct UpdateAvailableHistoryCell {
+    latest_version: String,
+    update_action: Option<UpdateAction>,
+}
+
+#[cfg_attr(debug_assertions, allow(dead_code))]
+impl UpdateAvailableHistoryCell {
+    pub(crate) fn new(latest_version: String, update_action: Option<UpdateAction>) -> Self {
+        Self {
+            latest_version,
+            update_action,
+        }
+    }
+}
+
+impl HistoryCell for UpdateAvailableHistoryCell {
+    fn display_lines(&self, width: u16) -> Vec<Line<'static>> {
+        use ratatui_macros::line;
+        use ratatui_macros::text;
+        let update_instruction = if let Some(update_action) = self.update_action {
+            line!["Run ", update_action.command_str().cyan(), " to update."]
+        } else {
+            line![
+                "See ",
+                "https://github.com/openai/codex".cyan().underlined(),
+                " for installation options."
+            ]
+        };
+
+        let content = text![
+            line![
+                padded_emoji("✨").bold().cyan(),
+                "Update available!".bold().cyan(),
+                " ",
+                format!("{CODEX_CLI_VERSION} -> {}", self.latest_version).bold(),
+            ],
+            update_instruction,
+            "",
+            "See full release notes:",
+            "https://github.com/openai/codex/releases/latest"
+                .cyan()
+                .underlined(),
+        ];
+
+        let inner_width = content
+            .width()
+            .min(usize::from(width.saturating_sub(4)))
+            .max(1);
+        with_border_with_inner_width(content.lines, inner_width)
+    }
+}
+
 #[derive(Debug)]
 pub(crate) struct PrefixedWrappedHistoryCell {
     text: Text<'static>,