Login flow polish (#3632)

# Description
- Update sign in flow

# Tests
- Passes CI

---------

Co-authored-by: Michael Bolin <mbolin@openai.com>

codex-rs/tui/src/onboarding/welcome.rs

@@ -3,23 +3,62 @@ use ratatui::layout::Rect;
 use ratatui::prelude::Widget;
 use ratatui::style::Stylize;
 use ratatui::text::Line;
+use ratatui::widgets::Paragraph;
 use ratatui::widgets::WidgetRef;
+use ratatui::widgets::Wrap;
 
+use crate::frames::FRAME_TICK_DEFAULT;
+use crate::frames::FRAMES_DEFAULT;
 use crate::onboarding::onboarding_screen::StepStateProvider;
+use crate::tui::FrameRequester;
 
 use super::onboarding_screen::StepState;
+use std::time::Duration;
+use std::time::Instant;
+
+const FRAME_TICK: Duration = FRAME_TICK_DEFAULT;
 
 pub(crate) struct WelcomeWidget {
     pub is_logged_in: bool,
+    pub request_frame: FrameRequester,
+    pub start: Instant,
 }
 
 impl WidgetRef for &WelcomeWidget {
     fn render_ref(&self, area: Rect, buf: &mut Buffer) {
-        let line = Line::from(vec![
-            ">_ ".into(),
-            "Welcome to Codex, OpenAI's command-line coding agent".bold(),
-        ]);
-        line.render(area, buf);
+        let elapsed_ms = self.start.elapsed().as_millis();
+
+        // Align next draw to the next FRAME_TICK boundary to reduce jitter.
+        {
+            let tick_ms = FRAME_TICK.as_millis();
+            let rem_ms = elapsed_ms % tick_ms;
+            let delay_ms = if rem_ms == 0 {
+                tick_ms
+            } else {
+                tick_ms - rem_ms
+            };
+            // Safe cast: delay_ms < tick_ms and FRAME_TICK is small.
+            self.request_frame
+                .schedule_frame_in(Duration::from_millis(delay_ms as u64));
+        }
+
+        let frames = &FRAMES_DEFAULT;
+        let idx = ((elapsed_ms / FRAME_TICK.as_millis()) % frames.len() as u128) as usize;
+
+        let mut lines: Vec<Line> = Vec::with_capacity(frames.len() + 2);
+        lines.extend(frames[idx].lines().map(|l| l.into()));
+
+        lines.push("".into());
+        lines.push(Line::from(vec![
+            "  ".into(),
+            "Welcome to ".into(),
+            "Codex".bold(),
+            ", OpenAI's command-line coding agent".into(),
+        ]));
+
+        Paragraph::new(lines)
+            .wrap(Wrap { trim: false })
+            .render(area, buf);
     }
 }
 
@@ -31,3 +70,14 @@ impl StepStateProvider for WelcomeWidget {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// A number of things break down if FRAME_TICK is zero.
+    #[test]
+    fn frame_tick_must_be_nonzero() {
+        assert!(FRAME_TICK.as_millis() > 0);
+    }
+}