tui: fix backtracking past /status (#6335)

Fixes https://github.com/openai/codex/issues/4722

Supersedes https://github.com/openai/codex/pull/5058

Ideally we'd have a clearer way of separating history per-session than
by detecting a specific history cell type, but this is a fairly minimal
fix for now.

codex-rs/tui/src/app_backtrack.rs

@@ -3,7 +3,7 @@ use std::path::PathBuf;
 use std::sync::Arc;
 
 use crate::app::App;
-use crate::history_cell::CompositeHistoryCell;
+use crate::history_cell::SessionInfoCell;
 use crate::history_cell::UserHistoryCell;
 use crate::pager_overlay::Overlay;
 use crate::tui;
@@ -394,13 +394,13 @@ fn nth_user_position(
 fn user_positions_iter(
     cells: &[Arc<dyn crate::history_cell::HistoryCell>],
 ) -> impl Iterator<Item = usize> + '_ {
-    let header_type = TypeId::of::<CompositeHistoryCell>();
+    let session_start_type = TypeId::of::<SessionInfoCell>();
     let user_type = TypeId::of::<UserHistoryCell>();
     let type_of = |cell: &Arc<dyn crate::history_cell::HistoryCell>| cell.as_any().type_id();
 
     let start = cells
         .iter()
-        .rposition(|cell| type_of(cell) == header_type)
+        .rposition(|cell| type_of(cell) == session_start_type)
         .map_or(0, |idx| idx + 1);
 
     cells

codex-rs/tui/src/history_cell.rs

@@ -559,11 +559,28 @@ pub(crate) fn padded_emoji(emoji: &str) -> String {
     format!("{emoji}\u{200A}")
 }
 
+#[derive(Debug)]
+pub struct SessionInfoCell(CompositeHistoryCell);
+
+impl HistoryCell for SessionInfoCell {
+    fn display_lines(&self, width: u16) -> Vec<Line<'static>> {
+        self.0.display_lines(width)
+    }
+
+    fn desired_height(&self, width: u16) -> u16 {
+        self.0.desired_height(width)
+    }
+
+    fn transcript_lines(&self, width: u16) -> Vec<Line<'static>> {
+        self.0.transcript_lines(width)
+    }
+}
+
 pub(crate) fn new_session_info(
     config: &Config,
     event: SessionConfiguredEvent,
     is_first_event: bool,
-) -> CompositeHistoryCell {
+) -> SessionInfoCell {
     let SessionConfiguredEvent {
         model,
         reasoning_effort,
@@ -573,7 +590,7 @@ pub(crate) fn new_session_info(
         initial_messages: _,
         rollout_path: _,
     } = event;
-    if is_first_event {
+    SessionInfoCell(if is_first_event {
         // Header box rendered as history (so it appears at the very top)
         let header = SessionHeaderHistoryCell::new(
             model,
@@ -632,7 +649,7 @@ pub(crate) fn new_session_info(
         CompositeHistoryCell {
             parts: vec![Box::new(PlainHistoryCell { lines })],
         }
-    }
+    })
 }
 
 pub(crate) fn new_user_prompt(message: String) -> UserHistoryCell {