fix(tui): add plain font style fallback

crates/jcode-tui/src/tui/ui.rs

@@ -60,6 +60,9 @@ use std::time::{Duration, Instant};
 #[cfg(test)]
 use unicode_width::UnicodeWidthStr;
 
+const PLAIN_FONT_STYLE_ENV: &str = "JCODE_TUI_PLAIN_FONT_STYLE";
+static PLAIN_FONT_STYLE_REQUESTED: OnceLock<bool> = OnceLock::new();
+
 #[path = "ui_animations.rs"]
 mod animations;
 #[path = "ui_box.rs"]
@@ -1964,6 +1967,54 @@ pub fn draw(frame: &mut Frame, app: &dyn TuiState) {
         Ok(()) => {}
         Err(payload) => render_recovered_panic_frame(frame, &payload),
     }
+    strip_font_variant_modifiers_if_requested(frame);
+}
+
+fn plain_font_style_requested() -> bool {
+    *PLAIN_FONT_STYLE_REQUESTED.get_or_init(|| {
+        std::env::var_os(PLAIN_FONT_STYLE_ENV)
+            .and_then(|value| value.into_string().ok())
+            .as_deref()
+            .is_some_and(parse_plain_font_style_value)
+    })
+}
+
+fn parse_plain_font_style_value(value: &str) -> bool {
+    let value = value.trim();
+    value == "1"
+        || value.eq_ignore_ascii_case("true")
+        || value.eq_ignore_ascii_case("yes")
+        || value.eq_ignore_ascii_case("on")
+}
+
+fn font_variant_modifiers() -> Modifier {
+    Modifier::BOLD | Modifier::DIM | Modifier::ITALIC | Modifier::REVERSED
+}
+
+fn strip_font_variant_modifiers_if_requested(frame: &mut Frame) {
+    let requested = plain_font_style_requested();
+    let frame_area = frame.area();
+    let buf = frame.buffer_mut();
+    let area = frame_area.intersection(*buf.area());
+    strip_font_variant_modifiers_if(buf, area, requested);
+}
+
+fn strip_font_variant_modifiers_if(buf: &mut ratatui::buffer::Buffer, area: Rect, requested: bool) {
+    if requested {
+        strip_font_variant_modifiers(buf, area);
+    }
+}
+
+fn strip_font_variant_modifiers(buf: &mut ratatui::buffer::Buffer, area: Rect) {
+    let modifiers = font_variant_modifiers();
+    for y in area.y..area.y.saturating_add(area.height) {
+        for x in area.x..area.x.saturating_add(area.width) {
+            let cell = &mut buf[(x, y)];
+            if cell.modifier.intersects(modifiers) {
+                cell.modifier.remove(modifiers);
+            }
+        }
+    }
 }
 
 fn draw_inner(frame: &mut Frame, app: &dyn TuiState) {
@@ -2797,6 +2848,74 @@ pub(crate) fn render_native_scrollbar(
     frame.render_widget(Paragraph::new(lines), area);
 }
 
+#[cfg(test)]
+mod font_style_tests {
+    use super::*;
+
+    fn styled_ascii_buffer() -> ratatui::buffer::Buffer {
+        let mut buffer = ratatui::buffer::Buffer::empty(Rect::new(0, 0, 32, 1));
+        let text = "browser continue Done Built";
+        for (x, ch) in text.chars().enumerate() {
+            let cell = &mut buffer[(x as u16, 0)];
+            cell.set_symbol(ch.encode_utf8(&mut [0; 4]));
+            cell.modifier
+                .insert(Modifier::BOLD | Modifier::DIM | Modifier::ITALIC | Modifier::REVERSED);
+        }
+        buffer
+    }
+
+    #[test]
+    fn parse_plain_font_style_value_accepts_truthy_values() {
+        for value in ["1", "true", "TRUE", "yes", "YES", "on", "ON", "  true  "] {
+            assert!(
+                parse_plain_font_style_value(value),
+                "{value:?} should enable plain font style"
+            );
+        }
+    }
+
+    #[test]
+    fn parse_plain_font_style_value_rejects_empty_and_falsey_values() {
+        for value in ["", "0", "false", "no", "off", "plain"] {
+            assert!(
+                !parse_plain_font_style_value(value),
+                "{value:?} should not enable plain font style"
+            );
+        }
+    }
+
+    #[test]
+    fn strip_font_variant_modifiers_if_is_noop_when_not_requested() {
+        let mut buffer = styled_ascii_buffer();
+
+        strip_font_variant_modifiers_if(&mut buffer, Rect::new(0, 0, 32, 1), false);
+
+        assert!(
+            buffer[(0, 0)].modifier.intersects(font_variant_modifiers()),
+            "font modifiers should remain when plain font style is disabled"
+        );
+    }
+
+    #[test]
+    fn strip_font_variant_modifiers_preserves_ascii_symbols() {
+        let mut buffer = styled_ascii_buffer();
+        let text = "browser continue Done Built";
+
+        strip_font_variant_modifiers(&mut buffer, Rect::new(0, 0, 32, 1));
+
+        let rendered: String = (0..text.len() as u16)
+            .map(|x| buffer[(x, 0)].symbol())
+            .collect();
+        assert_eq!(rendered, text);
+        for x in 0..text.len() as u16 {
+            assert!(
+                !buffer[(x, 0)].modifier.intersects(font_variant_modifiers()),
+                "cell {x} should not keep font-variant modifiers"
+            );
+        }
+    }
+}
+
 #[cfg(test)]
 #[path = "ui_tests/mod.rs"]
 mod tests;