tui: bring the transcript closer to display mode (#4848)

before
<img width="1161" height="836" alt="Screenshot 2025-10-06 at 3 06 52 PM"
src="https://github.com/user-attachments/assets/7622fd6b-9d37-402f-8651-61c2c55dcbc6"
/>

after
<img width="1161" height="858" alt="Screenshot 2025-10-06 at 3 07 02 PM"
src="https://github.com/user-attachments/assets/1498f327-1d1a-4630-951f-7ca371ab0139"
/>

codex-rs/tui/src/render/mod.rs

@@ -38,11 +38,13 @@ pub trait RectExt {
 
 impl RectExt for Rect {
     fn inset(&self, insets: Insets) -> Rect {
+        let horizontal = insets.left.saturating_add(insets.right);
+        let vertical = insets.top.saturating_add(insets.bottom);
         Rect {
-            x: self.x + insets.left,
-            y: self.y + insets.top,
-            width: self.width - insets.left - insets.right,
-            height: self.height - insets.top - insets.bottom,
+            x: self.x.saturating_add(insets.left),
+            y: self.y.saturating_add(insets.top),
+            width: self.width.saturating_sub(horizontal),
+            height: self.height.saturating_sub(vertical),
         }
     }
 }

codex-rs/tui/src/render/renderable.rs

@@ -1,3 +1,5 @@
+use std::sync::Arc;
+
 use ratatui::buffer::Buffer;
 use ratatui::layout::Rect;
 use ratatui::text::Line;
@@ -12,6 +14,12 @@ pub trait Renderable {
     fn desired_height(&self, width: u16) -> u16;
 }
 
+impl<R: Renderable + 'static> From<R> for Box<dyn Renderable> {
+    fn from(value: R) -> Self {
+        Box::new(value)
+    }
+}
+
 impl Renderable for () {
     fn render(&self, _area: Rect, _buf: &mut Buffer) {}
     fn desired_height(&self, _width: u16) -> u16 {
@@ -71,6 +79,15 @@ impl<R: Renderable> Renderable for Option<R> {
     }
 }
 
+impl<R: Renderable> Renderable for Arc<R> {
+    fn render(&self, area: Rect, buf: &mut Buffer) {
+        self.as_ref().render(area, buf);
+    }
+    fn desired_height(&self, width: u16) -> u16 {
+        self.as_ref().desired_height(width)
+    }
+}
+
 pub struct ColumnRenderable {
     children: Vec<Box<dyn Renderable>>,
 }
@@ -122,7 +139,10 @@ impl Renderable for InsetRenderable {
 }
 
 impl InsetRenderable {
-    pub fn new(child: Box<dyn Renderable>, insets: Insets) -> Self {
-        Self { child, insets }
+    pub fn new(child: impl Into<Box<dyn Renderable>>, insets: Insets) -> Self {
+        Self {
+            child: child.into(),
+            insets,
+        }
     }
 }