fix: make overlay() ANSI-aware using visible character positions

render.ts

@@ -34,10 +34,33 @@ export function joinText(parts: string[], separator: string): string {
   return parts.filter(Boolean).join(` ${separator} `);
 }
 
+// ANSI-Aware Slice - Extract a substring by visible character positions,
+// preserving ANSI escape codes that precede visible characters.
+function ansiSlice(text: string, start: number, end: number): string {
+  let output = "";
+  let visible = 0;
+  for (let i = 0; i < text.length; i++) {
+    if (text[i] === "\x1b") {
+      const match = text.slice(i).match(ANSI_PREFIX_RE);
+      if (match) {
+        if (visible >= start && visible < end) output += match[0];
+        i += match[0].length - 1;
+        continue;
+      }
+    }
+    if (visible >= start && visible < end) output += text[i];
+    visible++;
+    if (visible >= end) break;
+  }
+  return output;
+}
+
 export function overlay(base: string, text: string): string {
-  if (visibleWidth(text) >= visibleWidth(base)) return truncate(text, visibleWidth(base));
+  const baseWidth = visibleWidth(base);
-  const start = Math.max(0, Math.floor((visibleWidth(base) - visibleWidth(text)) / 2));
+  const textWidth = visibleWidth(text);
-  return `${base.slice(0, start)}${text}${base.slice(start + visibleWidth(text))}`;
+  if (textWidth >= baseWidth) return truncate(text, baseWidth);
+  const start = Math.max(0, Math.floor((baseWidth - textWidth) / 2));
+  return `${ansiSlice(base, 0, start)}${text}${ansiSlice(base, start + textWidth, baseWidth)}`;
 }
 
 function dimText(text: string, theme?: any): string {