feat(tui): harden theme fallback contracts and diff wrapping

codex-rs/tui/src/app.rs

@@ -2825,10 +2825,7 @@ impl App {
             return;
         }
 
-        let auto_theme_name = match crate::terminal_palette::default_bg() {
-            Some(bg) if crate::color::is_light(bg) => "catppuccin-latte",
-            _ => "catppuccin-mocha",
-        };
+        let auto_theme_name = crate::render::highlight::adaptive_default_theme_name();
         if let Some(theme) = crate::render::highlight::resolve_theme_by_name(
             auto_theme_name,
             Some(&self.config.codex_home),

codex-rs/tui/src/diff_render.rs

@@ -590,40 +590,26 @@ fn push_wrapped_diff_line_inner(
         return lines;
     }
 
-    // Fallback: no syntax spans — use the original wrapping behavior.
-    let mut remaining_text: &str = text;
-    let mut first = true;
+    let available_content_cols = width.saturating_sub(prefix_cols + 1).max(1);
+    let styled = vec![RtSpan::styled(text.to_string(), line_style)];
+    let wrapped_chunks = wrap_styled_spans(&styled, available_content_cols);
+
     let mut lines: Vec<RtLine<'static>> = Vec::new();
-
-    loop {
-        let available_content_cols = width.saturating_sub(prefix_cols + 1).max(1);
-        let split_at_byte_index = remaining_text
-            .char_indices()
-            .nth(available_content_cols)
-            .map(|(i, _)| i)
-            .unwrap_or_else(|| remaining_text.len());
-        let (chunk, rest) = remaining_text.split_at(split_at_byte_index);
-        remaining_text = rest;
-
-        if first {
+    for (i, chunk) in wrapped_chunks.into_iter().enumerate() {
+        let mut row_spans: Vec<RtSpan<'static>> = Vec::new();
+        if i == 0 {
             let gutter = format!("{ln_str:>gutter_width$} ");
-            let content = format!("{sign_char}{chunk}");
-            lines.push(RtLine::from(vec![
-                RtSpan::styled(gutter, style_gutter()),
-                RtSpan::styled(content, line_style),
-            ]));
-            first = false;
+            let sign = format!("{sign_char}");
+            row_spans.push(RtSpan::styled(gutter, style_gutter()));
+            row_spans.push(RtSpan::styled(sign, line_style));
         } else {
-            let gutter = format!("{:gutter_width$}  ", "");
-            lines.push(RtLine::from(vec![
-                RtSpan::styled(gutter, style_gutter()),
-                RtSpan::styled(chunk.to_string(), line_style),
-            ]));
-        }
-        if remaining_text.is_empty() {
-            break;
+            let cont_gutter = format!("{:gutter_width$}  ", "");
+            row_spans.push(RtSpan::styled(cont_gutter, style_gutter()));
         }
+        row_spans.extend(chunk);
+        lines.push(RtLine::from(row_spans));
     }
+
     lines
 }
 
@@ -758,6 +744,19 @@ mod tests {
         assert_snapshot!(name, terminal.backend());
     }
 
+    fn display_width(text: &str) -> usize {
+        text.chars()
+            .map(|ch| ch.width().unwrap_or(if ch == '\t' { TAB_WIDTH } else { 0 }))
+            .sum()
+    }
+
+    fn line_display_width(line: &RtLine<'static>) -> usize {
+        line.spans
+            .iter()
+            .map(|span| display_width(span.content.as_ref()))
+            .sum()
+    }
+
     fn snapshot_lines_text(name: &str, lines: &[RtLine<'static>]) {
         // Convert Lines to plain text rows and trim trailing spaces so it's
         // easier to validate indentation visually in snapshots.
@@ -1285,6 +1284,26 @@ mod tests {
         }
     }
 
+    #[test]
+    fn fallback_wrapping_uses_display_width_for_tabs_and_wide_chars() {
+        let width = 8;
+        let lines = push_wrapped_diff_line(
+            1,
+            DiffLineType::Insert,
+            "abcd\t界🙂",
+            width,
+            line_number_width(1),
+        );
+
+        assert!(lines.len() >= 2, "expected wrapped output, got {lines:?}");
+        for line in &lines {
+            assert!(
+                line_display_width(line) <= width,
+                "fallback wrapped line exceeded width {width}: {line:?}"
+            );
+        }
+    }
+
     #[test]
     fn large_update_diff_skips_highlighting() {
         // Build a patch large enough to exceed MAX_HIGHLIGHT_LINES (10_000).

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

@@ -51,8 +51,14 @@ fn syntax_set() -> &'static SyntaxSet {
     SYNTAX_SET.get_or_init(two_face::syntax::extra_newlines)
 }
 
-/// Set the user-configured theme override before any highlighting occurs.
-/// Must be called at most once, before the first call to `theme()`.
+/// Set the user-configured syntax theme override and codex home path.
+///
+/// Call this with the **final resolved config** (after onboarding, resume, and
+/// fork reloads complete). The first call persists `name` and `codex_home` in
+/// `OnceLock`s used by startup/default theme resolution.
+///
+/// Subsequent calls cannot change the persisted `OnceLock` values, but they
+/// still update the runtime theme immediately for live preview flows.
 ///
 /// Returns a warning message when the configured theme name cannot be
 /// resolved to a bundled theme or a custom `.tmTheme` file on disk.
@@ -162,6 +168,25 @@ fn load_custom_theme(name: &str, codex_home: &Path) -> Option<Theme> {
     ThemeSet::get_theme(custom_theme_path(name, codex_home)).ok()
 }
 
+fn adaptive_default_theme_selection() -> (EmbeddedThemeName, &'static str) {
+    match crate::terminal_palette::default_bg() {
+        Some(bg) if crate::color::is_light(bg) => {
+            (EmbeddedThemeName::CatppuccinLatte, "catppuccin-latte")
+        }
+        _ => (EmbeddedThemeName::CatppuccinMocha, "catppuccin-mocha"),
+    }
+}
+
+fn adaptive_default_embedded_theme_name() -> EmbeddedThemeName {
+    adaptive_default_theme_selection().0
+}
+
+/// Return the kebab-case name of the adaptive default syntax theme selected
+/// from terminal background lightness.
+pub(crate) fn adaptive_default_theme_name() -> &'static str {
+    adaptive_default_theme_selection().1
+}
+
 /// Build the theme from current override/auto-detection settings.
 /// Extracted from the old `theme()` init closure so it can be reused.
 fn resolve_theme_with_override(name: Option<&str>, codex_home: Option<&Path>) -> Theme {
@@ -182,12 +207,7 @@ fn resolve_theme_with_override(name: Option<&str>, codex_home: Option<&Path>) ->
         tracing::warn!("unknown syntax theme \"{name}\", falling back to auto-detection");
     }
 
-    // Adaptive default: light or dark based on terminal background.
-    let name = match crate::terminal_palette::default_bg() {
-        Some(bg) if crate::color::is_light(bg) => EmbeddedThemeName::CatppuccinLatte,
-        _ => EmbeddedThemeName::CatppuccinMocha,
-    };
-    ts.get(name).clone()
+    ts.get(adaptive_default_embedded_theme_name()).clone()
 }
 
 /// Build the theme from current override/auto-detection settings.
@@ -234,11 +254,7 @@ pub(crate) fn current_theme_name() -> String {
             return name.clone();
         }
     }
-    // Adaptive default: light or dark based on terminal background.
-    match crate::terminal_palette::default_bg() {
-        Some(bg) if crate::color::is_light(bg) => "catppuccin-latte".to_string(),
-        _ => "catppuccin-mocha".to_string(),
-    }
+    adaptive_default_theme_name().to_string()
 }
 
 /// Resolve a theme name to a `Theme` (bundled or custom). Returns `None`

codex-rs/tui/src/theme_picker.rs

@@ -356,12 +356,13 @@ pub(crate) fn build_theme_picker_params(
         })
         .collect();
 
-    // Capture theme names from the stable entry list built above so the
-    // preview closure indexes into the same ordering the picker uses.
-    let preview_names: Vec<String> = entries.iter().map(|e| e.name.clone()).collect();
+    // Derive preview targets from the final `items` list (not from `entries`)
+    // so preview ordering stays aligned if item construction/sorting changes.
+    let preview_theme_names: Vec<Option<String>> =
+        items.iter().map(|item| item.search_value.clone()).collect();
     let preview_home = codex_home_owned.clone();
     let on_selection_changed = Some(Box::new(move |idx: usize, _tx: &_| {
-        if let Some(name) = preview_names.get(idx)
+        if let Some(Some(name)) = preview_theme_names.get(idx)
             && let Some(theme) = highlight::resolve_theme_by_name(name, preview_home.as_deref())
         {
             highlight::set_syntax_theme(theme);
@@ -471,6 +472,15 @@ mod tests {
         assert!(params.stacked_side_content.is_some());
     }
 
+    #[test]
+    fn theme_picker_items_include_search_values_for_preview_mapping() {
+        let params = build_theme_picker_params(None, None, None);
+        assert!(
+            params.items.iter().all(|item| item.search_value.is_some()),
+            "theme picker preview mapping relies on item search_value to stay aligned with final item order"
+        );
+    }
+
     #[test]
     fn wide_preview_renders_all_lines_with_vertical_center_and_left_inset() {
         let lines = render_lines(&ThemePreviewWideRenderable, 80, 20);