fix(cli): eliminate TUI flash on key navigation entirely

Replace terminal.clear() with a zero-flash technique: toggle an invisible
BOLD modifier on all cells in the translations panel when the key changes.
Bold-on-space is visually identical to normal-space, but ratatui's diff
renderer treats it as "changed" and re-sends every cell in the area,
overwriting ghost glyphs from Arabic/Bengali/Hindi complex-script characters.

Previously, terminal.clear() sent a ClearType::All escape code causing a
full-screen flash. The later "detect complex scripts" heuristic was also
ineffective because multilingual files have complex-script translations on
every key.

The fix is purely in ratatui's buffer layer — no escape codes, no screen
blanking. frame.buffer_mut().set_style() stamps the alternating style onto
all cells before any widget renders; widgets overwrite content cells with
their own styles, so only empty cells retain the toggled BOLD, keeping them
visually invisible while forcing a diff-driven re-send.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: WendellXY

langcodec-cli/src/editor/app.rs

@@ -75,6 +75,10 @@ pub struct App {
     pub translation_scroll: u16,
     /// Set to true while waiting for delete confirmation
     pub confirm_delete: bool,
+    /// Toggled on every key navigation; used by the renderer to force
+    /// ratatui's diff to re-send all cells in the translations panel,
+    /// eliminating ghost glyphs from complex-script characters.
+    pub redraw_token: bool,
 }
 
 impl App {
@@ -128,6 +132,7 @@ impl App {
             split_ratio: 38,
             translation_scroll: 0,
             confirm_delete: false,
+            redraw_token: false,
         }
     }
 
@@ -396,6 +401,7 @@ impl App {
             self.dirty = true;
             self.status_message =
                 Some((format!("Deleted key '{key}'"), StatusTone::Success));
+            self.redraw_token = !self.redraw_token;
         }
         self.confirm_delete = false;
         self.input_mode = InputMode::Normal;
@@ -416,6 +422,7 @@ impl App {
                 self.key_list_state.select(Some(idx));
                 self.translation_scroll = 0;
                 self.status_message = None;
+                self.redraw_token = !self.redraw_token;
                 return;
             }
         }
@@ -435,6 +442,7 @@ impl App {
                 self.key_list_state.select(Some(idx));
                 self.translation_scroll = 0;
                 self.status_message = None;
+                self.redraw_token = !self.redraw_token;
                 return;
             }
         }
@@ -468,6 +476,7 @@ impl App {
         self.key_list_state.select(Some(next));
         self.translation_scroll = 0;
         self.status_message = None;
+        self.redraw_token = !self.redraw_token;
     }
 
     pub fn key_prev(&mut self) {
@@ -482,6 +491,7 @@ impl App {
         self.key_list_state.select(Some(prev));
         self.translation_scroll = 0;
         self.status_message = None;
+        self.redraw_token = !self.redraw_token;
     }
 
     pub fn key_next_page(&mut self, page_size: usize) {
@@ -497,6 +507,7 @@ impl App {
         self.key_list_state.select(Some(next));
         self.translation_scroll = 0;
         self.status_message = None;
+        self.redraw_token = !self.redraw_token;
     }
 
     pub fn key_prev_page(&mut self, page_size: usize) {
@@ -511,13 +522,15 @@ impl App {
         self.key_list_state.select(Some(prev));
         self.translation_scroll = 0;
         self.status_message = None;
+        self.redraw_token = !self.redraw_token;
     }
 
     pub fn key_jump_top(&mut self) {
         if !self.filtered_keys.is_empty() {
             self.key_list_state.select(Some(0));
             self.translation_scroll = 0;
             self.status_message = None;
+            self.redraw_token = !self.redraw_token;
         }
     }
 
@@ -527,6 +540,7 @@ impl App {
                 .select(Some(self.filtered_keys.len() - 1));
             self.translation_scroll = 0;
             self.status_message = None;
+            self.redraw_token = !self.redraw_token;
         }
     }
 

langcodec-cli/src/editor/mod.rs

@@ -87,8 +87,6 @@ pub fn run_browse_command(opts: BrowseOptions) -> Result<(), String> {
 
     let mut term = TermGuard::new()?;
 
-    let mut prev_key_idx = app.key_list_state.selected();
-
     loop {
         term.terminal
             .draw(|frame| ui::render(frame, &mut app))
@@ -101,62 +99,8 @@ pub fn run_browse_command(opts: BrowseOptions) -> Result<(), String> {
             if let HandlerResult::Quit = handle_event(&mut app, event) {
                 break;
             }
-            // Complex-script glyphs (Arabic, Bengali, Hindi, …) can render wider
-            // than unicode-width reports, leaving ghost cells that ratatui's diff
-            // renderer won't overwrite.  A full terminal clear fixes this, but it
-            // causes a visible flash on every navigation.  Only clear when the
-            // old or new key actually contains complex-script text.
-            let cur_key_idx = app.key_list_state.selected();
-            if cur_key_idx != prev_key_idx {
-                let old_key = prev_key_idx.and_then(|i| app.filtered_keys.get(i).cloned());
-                let new_key = cur_key_idx.and_then(|i| app.filtered_keys.get(i).cloned());
-                prev_key_idx = cur_key_idx;
-
-                let needs_clear = [old_key, new_key].iter().any(|k| {
-                    k.as_ref().map(|key| {
-                        app.languages.iter().any(|lang| {
-                            app.get_translation(key, lang)
-                                .map(|v| has_complex_scripts(&v))
-                                .unwrap_or(false)
-                        })
-                    }).unwrap_or(false)
-                });
-
-                if needs_clear {
-                    term.terminal.clear().ok();
-                }
-            }
         }
     }
 
     Ok(())
 }
-
-/// Returns true if the string contains characters from scripts whose glyphs
-/// commonly render wider than unicode-width predicts (Arabic, Devanagari,
-/// Bengali, Tamil, Thai, Gujarati, Gurmukhi, Kannada, Malayalam, Telugu, …).
-/// Used to decide whether a full terminal clear is needed to avoid artifacts.
-fn has_complex_scripts(s: &str) -> bool {
-    s.chars().any(|c| {
-        let cp = c as u32;
-        matches!(cp,
-            0x0600..=0x06FF  // Arabic
-            | 0x0750..=0x077F // Arabic Supplement
-            | 0xFB50..=0xFDFF // Arabic Pres. Forms-A
-            | 0xFE70..=0xFEFF // Arabic Pres. Forms-B
-            | 0x0900..=0x097F // Devanagari (Hindi, Marathi, …)
-            | 0x0980..=0x09FF // Bengali / Assamese
-            | 0x0A00..=0x0A7F // Gurmukhi (Punjabi)
-            | 0x0A80..=0x0AFF // Gujarati
-            | 0x0B00..=0x0B7F // Odia
-            | 0x0B80..=0x0BFF // Tamil
-            | 0x0C00..=0x0C7F // Telugu
-            | 0x0C80..=0x0CFF // Kannada
-            | 0x0D00..=0x0D7F // Malayalam
-            | 0x0E00..=0x0E7F // Thai
-            | 0x0E80..=0x0EFF // Lao
-            | 0x0F00..=0x0FFF // Tibetan
-            | 0x1000..=0x109F // Myanmar
-        )
-    })
-}

langcodec-cli/src/editor/ui.rs

@@ -115,10 +115,22 @@ fn render_key_list(frame: &mut Frame, app: &mut App, area: Rect) {
 // ── Translations panel ────────────────────────────────────────────────────────
 
 fn render_translations(frame: &mut Frame, app: &App, area: Rect) {
-    // Clear the whole area first to prevent stale cells from complex-script
-    // characters whose terminal display width differs from unicode-width reports.
+    // Clear the whole area first to remove stale characters from previous render.
     frame.render_widget(Clear, area);
 
+    // Force ratatui's diff renderer to re-send every cell in this panel when
+    // the key changes.  We toggle between two invisible styles (BOLD on/off for
+    // spaces) so ratatui sees each cell as "changed" and overwrites any ghost
+    // glyphs left by complex-script characters (Arabic, Bengali, Hindi, …) whose
+    // terminal display width exceeds what unicode-width reports.  Without this,
+    // ratatui's diff skips cells it thinks are unchanged and ghost glyphs persist.
+    let ghost_fix_style = if app.redraw_token {
+        Style::default().add_modifier(Modifier::BOLD)
+    } else {
+        Style::default()
+    };
+    frame.buffer_mut().set_style(area, ghost_fix_style);
+
     let in_edit = matches!(app.input_mode, InputMode::Edit);
 
     // Translations panel is "active" (Cyan border) during edit mode