diff --git a/src/dashboard.ts b/src/dashboard.ts
index 9e4b857e..1e61b975 100644
--- a/src/dashboard.ts
+++ b/src/dashboard.ts
@@ -20,7 +20,7 @@ initTheme();
 
 function truncatedNoticeHtml(key: string, total: number | undefined): string {
   if (total === undefined || total <= UI_TRUNCATION_MAX) return "";
-  return `<div class="truncated-notice">Showing last ${UI_TRUNCATION_MAX} of ${total} ${key}</div>`;
+  return `<div class="truncated-notice">Showing last ${UI_TRUNCATION_MAX} of ${total} ${escapeHtml(key)}</div>`;
 }
 
 function truncatedNoticeText(key: string, total: number | undefined): string {
@@ -1075,14 +1075,16 @@ document.addEventListener("DOMContentLoaded", async () => {
   function createTranscriptEntryHTML(entry: TranscriptEntry): string {
     const timeStr = escapeHtml(entry.timestampLabel || formatDuration(entry.timestamp || 0));
     const speaker = escapeHtml(entry.speaker || "Unknown");
-    const initials = (entry.speaker || "Unknown")
+    const initials = speaker
       .split(" ")
       .filter(Boolean)
       .map((w) => w[0])
       .join("")
       .toUpperCase()
       .slice(0, 2);
-    const isAudio = (entry.speaker || "") === "Audio";
+    // speaker is already escapeHtml'd above, and "Audio" is pure ASCII
+    // so the comparison is safe (escapeHtml is a no-op for plain ASCII).
+    const isAudio = speaker === "Audio";
     const text = escapeHtml(entry.text || "");
     const chunkId = entry.id ? `transcript-${escapeHtml(entry.id)}` : "";
 
@@ -1095,9 +1097,9 @@ document.addEventListener("DOMContentLoaded", async () => {
           <div class="transcript-text">${text}</div>
         </div>
         <button type="button" class="copy-transcript-btn" 
-                data-speaker="${speaker}" 
-                data-time="${timeStr}" 
-                data-message="${text}" 
+                data-speaker="${sanitizeDataAttr(speaker)}" 
+                data-time="${sanitizeDataAttr(timeStr)}" 
+                data-message="${sanitizeDataAttr(text)}" 
                 title="Copy message to clipboard" 
                 aria-label="Copy message to clipboard">
           <svg xmlns="http://www.w3.org/2000/svg" width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="icon"><path d="M16 4h2a2 2 0 0 1 2 2v14a2 2 0 0 1-2 2H6a2 2 0 0 1-2-2V6a2 2 0 0 1 2-2h2"></path><rect x="8" y="2" width="8" height="4" rx="1" ry="1"></rect></svg>
@@ -2113,7 +2115,7 @@ function getEmptyStateHTML(message: string, isList: boolean = false): string {
           <line x1="12" x2="12" y1="19" y2="22"></line>
         </svg>
       </div>
-      <div class="empty-state-title">${message}</div>
+      <div class="empty-state-title">${escapeHtml(message)}</div>
     </${tag}>
   `;
 }
diff --git a/src/utils/domHelpers.test.ts b/src/utils/domHelpers.test.ts
new file mode 100644
index 00000000..f6e7671d
--- /dev/null
+++ b/src/utils/domHelpers.test.ts
@@ -0,0 +1,103 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { escapeHtml, formatDuration, sanitizeTopicStatus } from "./domHelpers";
+
+test("escapeHtml prevents XSS", () => {
+  assert.equal(escapeHtml(null), "");
+  assert.equal(escapeHtml(undefined), "");
+
+  assert.equal(escapeHtml(""), "");
+  assert.equal(escapeHtml("Alice"), "Alice");
+  assert.equal(escapeHtml("O'Brien"), "O&#039;Brien");
+  assert.equal(escapeHtml('Say "hello"'), "Say &quot;hello&quot;");
+  assert.equal(escapeHtml("a < b"), "a &lt; b");
+  assert.equal(escapeHtml("a > b"), "a &gt; b");
+  assert.equal(escapeHtml("M&Ms"), "M&amp;Ms");
+
+  const xss = '<script>alert("xss")</script>';
+  assert.equal(escapeHtml(xss), "&lt;script&gt;alert(&quot;xss&quot;)&lt;/script&gt;");
+
+  const imgXss = '<img src=x onerror="alert(1)">';
+  assert.equal(escapeHtml(imgXss), "&lt;img src=x onerror=&quot;alert(1)&quot;&gt;");
+
+  const safe = escapeHtml(xss);
+  assert.ok(!safe.includes("<script>"));
+  assert.ok(!safe.includes("</script>"));
+  assert.ok(!safe.includes('"'));
+});
+
+test("escapeHtml handles edge cases", () => {
+  assert.equal(escapeHtml("   "), "   ");
+  assert.equal(escapeHtml("a".repeat(1000)), "a".repeat(1000));
+
+  assert.equal(escapeHtml("Jack &amp; Jill"), "Jack &amp;amp; Jill");
+
+  assert.equal(escapeHtml("\n\t"), "\n\t");
+});
+
+test("escapeHtml in attribute context prevents injection", () => {
+  const name = 'John "Drop Table" Doe';
+  const escaped = escapeHtml(name);
+  const attr = `data-name="${escaped}"`;
+  assert.equal(attr, 'data-name="John &quot;Drop Table&quot; Doe"');
+
+  const singleQuote = "O'Brien";
+  const escaped2 = escapeHtml(singleQuote);
+  const attr2 = `data-author="${escaped2}"`;
+  assert.equal(attr2, 'data-author="O&#039;Brien"');
+});
+
+test("regression: malicious speaker name in transcript entry pattern", () => {
+  const malicious = '<script>alert("xss")</script>';
+  const speaker = escapeHtml(malicious);
+
+  const initials = speaker
+    .split(" ")
+    .filter(Boolean)
+    .map((w) => w[0])
+    .join("")
+    .toUpperCase()
+    .slice(0, 2);
+
+  assert.equal(initials, "&");
+  assert.ok(!initials.includes("<"));
+  assert.ok(!initials.includes(">"));
+  assert.ok(!initials.includes('"'));
+
+  const html = `<div class="transcript-speaker">${speaker}</div>`;
+  assert.ok(!html.includes("<script>"));
+  assert.ok(html.includes("&lt;script&gt;"));
+});
+
+test("escapeHtml output is safe when embedded in innerHTML", () => {
+  const payloads = [
+    '<script>alert("xss")</script>',
+    '<img src=x onerror="alert(1)">',
+    '"><script>alert(1)</script>',
+    "javascript:alert(1)",
+    "<<script>script>alert(1)</script>",
+  ];
+
+  for (const payload of payloads) {
+    const escaped = escapeHtml(payload);
+    assert.ok(!escaped.includes("<script>"), `payload still contains <script>: ${payload}`);
+    assert.ok(!escaped.includes("</script>"), `payload still contains </script>: ${payload}`);
+    assert.ok(!escaped.includes('"'), `payload still contains double quote: ${payload}`);
+  }
+});
+
+test("formatDuration", () => {
+  assert.equal(formatDuration(0), "00:00:00");
+  assert.equal(formatDuration(90), "00:01:30");
+  assert.equal(formatDuration(3661), "01:01:01");
+  assert.equal(formatDuration(86399), "23:59:59");
+  assert.equal(formatDuration(360000), "100:00:00");
+});
+
+test("sanitizeTopicStatus", () => {
+  assert.equal(sanitizeTopicStatus("completed"), "completed");
+  assert.equal(sanitizeTopicStatus("unresolved"), "unresolved");
+  assert.equal(sanitizeTopicStatus("active"), "active");
+  assert.equal(sanitizeTopicStatus("pending"), "active");
+  assert.equal(sanitizeTopicStatus(""), "active");
+});
diff --git a/src/utils/sanitize.test.ts b/src/utils/sanitize.test.ts
index 3c3e15fa..532e3393 100644
--- a/src/utils/sanitize.test.ts
+++ b/src/utils/sanitize.test.ts
@@ -1,54 +1,23 @@
 import assert from "node:assert/strict";
 import test from "node:test";
-import { escapeHtml, sanitizeClassName, sanitizeDataAttr } from "./sanitize";
+import { escapeHtml } from "./domHelpers";
+import { sanitizeClassName, sanitizeDataAttr } from "./sanitize";
 
-// Mock document for testing escapeHtml in Node.js environment
-const mockDiv = {
-  _textContent: "",
-  set textContent(val: string) {
-    this._textContent = val;
-    this.innerHTML = val.replace(/[&<>"']/g, (char) => {
-      const map: Record<string, string> = {
-        "&": "&amp;",
-        "<": "&lt;",
-        ">": "&gt;",
-        '"': "&quot;",
-        "'": "&#39;",
-      };
-      return map[char] || char;
-    });
-  },
-  get textContent() {
-    return this._textContent;
-  },
-  innerHTML: "",
-};
-
-(globalThis as any).document = {
-  createElement(tag: string) {
-    if (tag === "div") {
-      return mockDiv;
-    }
-    throw new Error(`Unsupported tag in mock: ${tag}`);
-  },
-};
-
-test("escapeHtml behavior", () => {
-  // Null/undefined inputs
+test("escapeHtml prevents XSS in text content", () => {
   assert.equal(escapeHtml(null), "");
   assert.equal(escapeHtml(undefined), "");
 
-  // Standard string inputs
+  assert.equal(escapeHtml(""), "");
   assert.equal(escapeHtml("hello"), "hello");
+  assert.equal(escapeHtml("Alice & Bob"), "Alice &amp; Bob");
   assert.equal(
     escapeHtml("<script>alert('xss')</script>"),
-    "&lt;script&gt;alert(&#39;xss&#39;)&lt;/script&gt;",
+    "&lt;script&gt;alert(&#039;xss&#039;)&lt;/script&gt;",
   );
 
-  // Non-string inputs
-  assert.equal(escapeHtml(42), "42");
-  assert.equal(escapeHtml(true), "true");
-  assert.equal(escapeHtml({ a: 1 }), "{&quot;a&quot;:1}");
+  const output = escapeHtml('<img src=x onerror="alert(1)">');
+  assert.equal(output, "&lt;img src=x onerror=&quot;alert(1)&quot;&gt;");
+  assert.ok(!output.includes('"'));
 });
 
 test("sanitizeClassName behavior", () => {
diff --git a/src/utils/sanitize.ts b/src/utils/sanitize.ts
index 861280a4..ef18b7b9 100644
--- a/src/utils/sanitize.ts
+++ b/src/utils/sanitize.ts
@@ -9,45 +9,17 @@
  */
 
 /**
- * Escapes HTML special characters in an arbitrary value to prevent XSS attacks.
+ * Escapes HTML special characters in a string to prevent XSS attacks.
  *
- * Accepts any type and converts it to a safe HTML string:
- * - `null` / `undefined` → `""`
- * - `string` → escaped as-is
- * - `number`, `boolean`, `symbol`, `bigint` → converted via `String()`
- * - objects / arrays → serialized via `JSON.stringify()`
- *
- * Internally delegates to a temporary `<div>` element so that the browser's
- * own HTML serialiser handles all edge cases (including supplementary Unicode
- * code points).
+ * @deprecated Use `escapeHtml` from `./domHelpers` instead — it has the same
+ *   contract for string values, is used by all rendering code, and works in
+ *   plain Node.js without a DOM mock. This re-export exists only to avoid
+ *   breaking existing imports during the migration.
  *
  * @param value - The raw, potentially untrusted value to escape.
- * @returns An HTML-safe string where `&`, `<`, `>`, `"`, and `'` are replaced
- *   with their corresponding HTML entities.
- *
- * @example
- * element.innerHTML = escapeHtml(userInput);
- * // '<script>alert(1)</script>' → '&lt;script&gt;alert(1)&lt;/script&gt;'
+ * @returns An HTML-safe string.
  */
-export function escapeHtml(value: unknown): string {
-  if (value === null || value === undefined) return "";
-  let str: string;
-  if (typeof value === "string") {
-    str = value;
-  } else if (
-    typeof value === "number" ||
-    typeof value === "boolean" ||
-    typeof value === "symbol" ||
-    typeof value === "bigint"
-  ) {
-    str = String(value);
-  } else {
-    str = JSON.stringify(value);
-  }
-  const div = document.createElement("div");
-  div.textContent = str;
-  return div.innerHTML;
-}
+export { escapeHtml } from "./domHelpers";
 
 /**
  * Validates a class name string against an explicit allowlist to prevent