fix(tui): highlight user messages in cached transcript

Route user cells in the transcript cache through the existing user-message renderer.

  The live chat view renders through lines_with_copy_metadata(), which previously
  bypassed the user-message highlight path. As a result, submitted user prompts did
  not show the intended full-row background in the main transcript.

  Add a regression test for the transcript cache path.

crates/tui/src/tui/history.rs

@@ -309,13 +309,9 @@ impl HistoryCell {
         options: TranscriptRenderOptions,
     ) -> Vec<RenderedTranscriptLine> {
         match self {
-            HistoryCell::User { content } => render_message_with_copy_metadata(
-                USER_GLYPH,
-                user_label_style(),
-                user_body_style(),
-                content,
-                width,
-            ),
+            HistoryCell::User { content } => {
+                hard_break_copy_lines(render_user_message(content, width))
+            }
             HistoryCell::Assistant { content, streaming } => render_message_with_copy_metadata(
                 ASSISTANT_GLYPH,
                 assistant_label_style_for(*streaming, options.low_motion),

crates/tui/src/tui/transcript.rs

@@ -554,6 +554,7 @@ fn truncate_spans_to_width(spans: Vec<Span<'static>>, max_width: usize) -> Vec<S
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::palette;
     use crate::tui::history::{ExecCell, ExecSource, HistoryCell, ToolCell, ToolStatus};
 
     fn plain_lines(cache: &TranscriptViewCache) -> Vec<String> {
@@ -595,6 +596,20 @@ mod tests {
         }))
     }
 
+    #[test]
+    fn cache_renders_user_cells_with_highlight_background() {
+        let cells = vec![user_cell("# literal user prompt")];
+        let revisions = vec![1u64];
+
+        let mut cache = TranscriptViewCache::new();
+        cache.ensure(&cells, &revisions, 40, TranscriptRenderOptions::default());
+
+        let lines = cache.lines();
+        assert_eq!(lines[0].style.bg, Some(palette::SURFACE_ELEVATED));
+        assert_eq!(lines[0].width(), 40);
+        assert_eq!(plain_lines(&cache)[0].trim_end(), "▎ # literal user prompt");
+    }
+
     #[test]
     fn cache_reuses_cells_when_revision_unchanged() {
         let cells = vec![