diff --git a/server/utils.test.ts b/server/utils.test.ts
index 61edc67..649ea5c 100644
--- a/server/utils.test.ts
+++ b/server/utils.test.ts
@@ -58,14 +58,37 @@ describe("charWidth", () => {
     expect(charWidth("🐼")).toBe(2);
   });
 
-  test("special ASCII art characters = 1", () => {
-    // Characters used in pet ASCII art
-    expect(charWidth("·")).toBe(1);  // middle dot (beaver eyes)
-    expect(charWidth("◉")).toBe(1);  // bullseye (lion eyes)
-    expect(charWidth("•")).toBe(1);  // bullet (golden/elephant eyes)
-    expect(charWidth("–")).toBe(1);  // en dash
-    expect(charWidth("…")).toBe(1);  // ellipsis
-    expect(charWidth("°")).toBe(1);  // degree (beaver slap)
+  test("special ASCII art characters = 1 on non-CJK locales", () => {
+    // Characters used in pet ASCII art. Pass cjk: false explicitly so the test
+    // is deterministic regardless of where the suite happens to run.
+    expect(charWidth("·", false)).toBe(1);  // middle dot (beaver eyes)
+    expect(charWidth("◉", false)).toBe(1);  // bullseye (lion eyes)
+    expect(charWidth("•", false)).toBe(1);  // bullet (golden/elephant eyes)
+    expect(charWidth("–", false)).toBe(1);  // en dash
+    expect(charWidth("…", false)).toBe(1);  // ellipsis
+    expect(charWidth("°", false)).toBe(1);  // degree (beaver slap)
+  });
+
+  test("Ambiguous-width art characters = 2 on CJK locales", () => {
+    // Same characters render double-wide on Chinese/Japanese/Korean Windows
+    // Terminal, iTerm2 in CJK locale, etc. Without this the right border of
+    // any padded box drifts on those terminals.
+    expect(charWidth("◉", true)).toBe(2);  // bullseye
+    expect(charWidth("—", true)).toBe(2);  // em dash
+    expect(charWidth("✦", true)).toBe(2);  // four-pointed star
+    expect(charWidth("✧", true)).toBe(2);  // four-pointed star outline
+    expect(charWidth("→", true)).toBe(2);  // rightwards arrow
+    expect(charWidth("★", true)).toBe(2);  // black star
+  });
+
+  test("box-drawing stays 1 even on CJK locales", () => {
+    // Every mainstream terminal special-cases box drawings to 1-wide for TUI
+    // sanity, even under a CJK locale. Borders would double otherwise.
+    expect(charWidth("─", true)).toBe(1);
+    expect(charWidth("│", true)).toBe(1);
+    expect(charWidth("╭", true)).toBe(1);
+    expect(charWidth("╮", true)).toBe(1);
+    expect(charWidth("├", true)).toBe(1);
   });
 
   test("braille blank = 1", () => {
diff --git a/server/utils.ts b/server/utils.ts
index 0d23931..19722b2 100644
--- a/server/utils.ts
+++ b/server/utils.ts
@@ -2,9 +2,49 @@
  * Shared utility functions — display width, padding, etc.
  */
 
-// ─── CJK display width (CJK = 2 cols, ASCII = 1) ─────────────────────────
+// ─── CJK locale detection ─────────────────────────────────────────────────
+//
+// On East Asian terminals (Chinese/Japanese/Korean Windows Terminal, iTerm2 in
+// CJK locale, etc.) Unicode "Ambiguous" East Asian Width characters render as
+// 2 columns instead of 1. The pet art uses a few of these (`◉`, `—`, `✦`, …)
+// so without locale awareness the right border of any padded box drifts on
+// CJK terminals — see issue #?.
+//
+// Detection order:
+//   1. POSIX env vars (LC_ALL / LC_CTYPE / LANG / LANGUAGE)
+//   2. Intl.DateTimeFormat resolved locale — works on Windows where the env
+//      vars are usually unset but the system locale is e.g. "zh-CN".
 
-export function charWidth(ch: string): number {
+const CJK_LOCALE_RE = /^(zh|ja|ko)\b/i;
+
+function detectCjkLocale(): boolean {
+  for (const v of [
+    process.env.LC_ALL,
+    process.env.LC_CTYPE,
+    process.env.LANG,
+    process.env.LANGUAGE,
+  ]) {
+    if (v && CJK_LOCALE_RE.test(v)) return true;
+  }
+  try {
+    const loc = Intl.DateTimeFormat().resolvedOptions().locale || "";
+    if (CJK_LOCALE_RE.test(loc)) return true;
+  } catch {
+    // Some restricted runtimes throw — fall through to false.
+  }
+  return false;
+}
+
+export const IS_CJK_LOCALE = detectCjkLocale();
+
+// ─── Display width ────────────────────────────────────────────────────────
+//
+// CJK = 2 cols, ASCII = 1, with locale-aware handling of Ambiguous-width
+// characters. Box-drawing chars (0x2500–0x257F) are intentionally excluded
+// from the Ambiguous-as-wide branch because every mainstream terminal
+// special-cases them to 1 column for TUI sanity even under a CJK locale.
+
+export function charWidth(ch: string, cjk: boolean = IS_CJK_LOCALE): number {
   const code = ch.codePointAt(0) ?? 0;
   if (code < 32 || (code >= 0x7f && code < 0xa0)) return 0;
   if (
@@ -22,15 +62,27 @@ export function charWidth(ch: string): number {
     (code >= 0x1f300 && code <= 0x1f9ff) ||
     (code >= 0x1fa00 && code <= 0x1faff)
   ) return 2;
+  if (cjk) {
+    if (
+      (code >= 0x2010 && code <= 0x2027) ||  // General Punctuation: em/en dash, quotes
+      (code >= 0x2030 && code <= 0x205e) ||  // More General Punctuation
+      (code >= 0x2150 && code <= 0x218f) ||  // Number Forms
+      (code >= 0x2190 && code <= 0x21ff) ||  // Arrows
+      (code >= 0x2200 && code <= 0x22ff) ||  // Mathematical Operators
+      (code >= 0x2580 && code <= 0x25ff) ||  // Block Elements + Geometric Shapes (covers ◉)
+      (code >= 0x2600 && code <= 0x26ff) ||  // Misc Symbols
+      (code >= 0x2700 && code <= 0x27bf)     // Dingbats (covers ✦ ✧)
+    ) return 2;
+  }
   return 1;
 }
 
-export function stringWidth(str: string): number {
+export function stringWidth(str: string, cjk: boolean = IS_CJK_LOCALE): number {
   return Array.from(str.replace(/\x1b\[[0-9;]*m/g, ""))
-    .reduce((sum, ch) => sum + charWidth(ch), 0);
+    .reduce((sum, ch) => sum + charWidth(ch, cjk), 0);
 }
 
-export function padDisplay(str: string, targetWidth: number): string {
-  const pad = Math.max(0, targetWidth - stringWidth(str));
+export function padDisplay(str: string, targetWidth: number, cjk: boolean = IS_CJK_LOCALE): string {
+  const pad = Math.max(0, targetWidth - stringWidth(str, cjk));
   return str + " ".repeat(pad);
 }