fix width of format-tab-title that returns embedded escapes

closes: #3481

docs/changelog.md

@@ -37,6 +37,8 @@ As features stabilize some brief notes about them will accumulate here.
   window which contained the pane in which the variable was changed. #3524
 * PNG images without an alpha channel could not be displayed by in the
   terminal. #3529.
+* tab width calculation when returning a string with embedded escape
+  sequences from a `format-tab-title` event handler. #3481
 
 ### 20230408-112425-69ae8472
 

wezterm-gui/src/tabbar.rs

@@ -84,8 +84,9 @@ fn call_format_tab_title(
                 }
                 _ => {
                     let s = String::from_lua(v, &*lua)?;
+                    let line = parse_status_text(&s, CellAttributes::default());
                     Ok(Some(TitleText {
-                        len: unicode_column_width(&s, None),
+                        len: line.len(),
                         items: vec![FormatItem::Text(s)],
                     }))
                 }