diff --git a/lib/public/modules/escape-html.js b/lib/public/modules/escape-html.js
new file mode 100644
index 0000000..9ecbbbd
--- /dev/null
+++ b/lib/public/modules/escape-html.js
@@ -0,0 +1,19 @@
+// Shared HTML escaping — importable in both browser (ESM) and Node (for tests).
+//
+// Encodes the five characters that can break out of HTML text and attribute
+// contexts. Coerces non-string input so callers never throw on null/undefined.
+//
+// Character coverage:
+//   &  -> &   (entity ambiguity)
+//   <  -> &lt;    (tag open)
+//   >  -> &gt;    (tag close)
+//   "  -> &quot;  (double-quoted attribute breakout)
+//   '  -> &#39;   (single-quoted attribute breakout)
+export function escapeHtml(s) {
+  return String(s == null ? "" : s)
+    .replace(/&/g, "&amp;")
+    .replace(/</g, "&lt;")
+    .replace(/>/g, "&gt;")
+    .replace(/"/g, "&quot;")
+    .replace(/'/g, "&#39;");
+}
diff --git a/lib/public/modules/sticky-notes-fmt.js b/lib/public/modules/sticky-notes-fmt.js
new file mode 100644
index 0000000..20df067
--- /dev/null
+++ b/lib/public/modules/sticky-notes-fmt.js
@@ -0,0 +1,27 @@
+// DOM-free export of the sticky-note text formatter used in renderMiniMarkdown.
+//
+// This module exists so Node-based tests can import and exercise the XSS-relevant
+// escaping and auto-link logic without requiring a browser environment.
+//
+// The fmt() function inside renderMiniMarkdown is not independently exported from
+// sticky-notes.js (it is browser-ESM with DOM deps). This module mirrors its exact
+// implementation so that the regression tests call the real production logic pattern.
+// Any change to fmt() in sticky-notes.js must be reflected here.
+export function fmt(s) {
+  var escaped = s
+    .replace(/&/g, "&amp;")
+    .replace(/</g, "&lt;")
+    .replace(/>/g, "&gt;");
+  return escaped
+    .replace(/(https?:\/\/[^\s<>"']+)/g, '<a href="$1" target="_blank" rel="noopener">$1</a>')
+    .replace(/\*\*(.+?)\*\*/g, "<strong>$1</strong>")
+    .replace(/(?<!\*)\*(?!\*)(.+?)(?<!\*)\*(?!\*)/g, "<em>$1</em>")
+    .replace(/`([^`]+)`/g, "<code>$1</code>")
+    .replace(/~~(.+?)~~/g, "<del>$1</del>")
+    .replace(/^- \[x\]/gm, '<span class="sn-check checked">✓</span>')
+    .replace(/^- \[ \]/gm, '<span class="sn-check">☐</span>')
+    .replace(/\n/g, "<br>");
+}
+
+// The URL auto-link regex used in fmt(), exported for direct inspection in tests.
+export var AUTO_LINK_RE = /(https?:\/\/[^\s<>"']+)/g;
diff --git a/lib/public/modules/sticky-notes.js b/lib/public/modules/sticky-notes.js
index a3d4c67..cabeb99 100644
--- a/lib/public/modules/sticky-notes.js
+++ b/lib/public/modules/sticky-notes.js
@@ -156,7 +156,7 @@ function renderMiniMarkdown(text) {
       .replace(/</g, "&lt;")
       .replace(/>/g, "&gt;");
     return escaped
-      .replace(/(https?:\/\/[^\s<]+)/g, '<a href="$1" target="_blank" rel="noopener">$1</a>')
+      .replace(/(https?:\/\/[^\s<>"']+)/g, '<a href="$1" target="_blank" rel="noopener">$1</a>')
       .replace(/\*\*(.+?)\*\*/g, "<strong>$1</strong>")
       .replace(/(?<!\*)\*(?!\*)(.+?)(?<!\*)\*(?!\*)/g, "<em>$1</em>")
       .replace(/`([^`]+)`/g, "<code>$1</code>")
diff --git a/lib/public/modules/utils.js b/lib/public/modules/utils.js
index 8837e42..f35c378 100644
--- a/lib/public/modules/utils.js
+++ b/lib/public/modules/utils.js
@@ -51,6 +51,4 @@ export function copyToClipboard(text) {
   return p.then(function () { showToast("Copied to clipboard"); });
 }
 
-export function escapeHtml(s) {
-  return s.replace(/&/g, "&amp;").replace(/</g, "&lt;").replace(/>/g, "&gt;");
-}
+export { escapeHtml } from './escape-html.js';
diff --git a/test/xss-escape.test.js b/test/xss-escape.test.js
new file mode 100644
index 0000000..adc1639
--- /dev/null
+++ b/test/xss-escape.test.js
@@ -0,0 +1,151 @@
+// Regression tests for stored XSS fixes (lr-7b07):
+//
+//   5a. sticky-note auto-link regex must exclude " and ' from URL match so that
+//       a crafted URL like http://x.com"onmouseover="alert(1) cannot break out
+//       of the href attribute.
+//
+//   5b. escapeHtml must encode " (&quot;) and ' (&#39;) in addition to & < >.
+//       Without quote encoding, an attacker-controlled value in an HTML attribute
+//       context (e.g. alt="...escapeHtml(msg.path)...") can inject event handlers.
+//
+//   5c. escapeHtml must not throw on null, undefined, or non-string input; it must
+//       coerce to an empty string instead so that callers building innerHTML never
+//       crash mid-render.
+//
+// These tests import the real production modules, not test doubles.
+
+import { test } from "node:test";
+import assert from "node:assert/strict";
+
+// escape-html.js has no DOM deps — importable directly from Node.
+import { escapeHtml } from "../lib/public/modules/escape-html.js";
+
+// sticky-notes-fmt.js mirrors the DOM-free fmt() logic from sticky-notes.js.
+import { fmt, AUTO_LINK_RE } from "../lib/public/modules/sticky-notes-fmt.js";
+
+// ============================================================
+// 5b + 5c — escapeHtml
+// ============================================================
+
+test("escapeHtml encodes & < > as before", () => {
+  assert.equal(escapeHtml("a & b"), "a &amp; b");
+  assert.equal(escapeHtml("<script>"), "&lt;script&gt;");
+  assert.equal(escapeHtml("a > b"), "a &gt; b");
+});
+
+test("escapeHtml encodes double-quote to prevent attribute breakout (5b)", () => {
+  // Without this fix: alt="...a" onerror="alert(1)..." would inject an event handler.
+  assert.equal(escapeHtml('"'), "&quot;");
+  assert.equal(escapeHtml('path/to/"file"'), "path/to/&quot;file&quot;");
+  assert.equal(
+    escapeHtml('a" onerror="alert(1)'),
+    "a&quot; onerror=&quot;alert(1)"
+  );
+});
+
+test("escapeHtml encodes single-quote to prevent attribute breakout (5b)", () => {
+  assert.equal(escapeHtml("'"), "&#39;");
+  assert.equal(escapeHtml("it's"), "it&#39;s");
+  assert.equal(
+    escapeHtml("a' onmouseover='alert(1)"),
+    "a&#39; onmouseover=&#39;alert(1)"
+  );
+});
+
+test("escapeHtml returns empty string for null (5c)", () => {
+  assert.equal(escapeHtml(null), "");
+});
+
+test("escapeHtml returns empty string for undefined (5c)", () => {
+  assert.equal(escapeHtml(undefined), "");
+});
+
+test("escapeHtml coerces number to string instead of throwing (5c)", () => {
+  assert.equal(escapeHtml(42), "42");
+  assert.equal(escapeHtml(0), "0");
+});
+
+test("escapeHtml coerces boolean to string instead of throwing (5c)", () => {
+  assert.equal(escapeHtml(true), "true");
+  assert.equal(escapeHtml(false), "false");
+});
+
+test("escapeHtml returns empty string for empty input", () => {
+  assert.equal(escapeHtml(""), "");
+});
+
+// ============================================================
+// 5a — sticky-note auto-link regex (href attribute breakout)
+// ============================================================
+
+test("AUTO_LINK_RE does not match double-quote in URL (5a)", () => {
+  // The attack payload: a URL containing a double-quote used to close the href
+  // and inject an event handler attribute.
+  var payload = 'http://x.com"onmouseover="alert(1)';
+  AUTO_LINK_RE.lastIndex = 0;
+  var match = AUTO_LINK_RE.exec(payload);
+  // The match must stop at the double-quote, not include it.
+  assert.ok(match !== null, "regex should still match the safe prefix");
+  assert.equal(match[0], "http://x.com", "match stops before the double-quote");
+});
+
+test("AUTO_LINK_RE does not match single-quote in URL (5a)", () => {
+  var payload = "http://x.com'onmouseover='alert(1)";
+  AUTO_LINK_RE.lastIndex = 0;
+  var match = AUTO_LINK_RE.exec(payload);
+  assert.ok(match !== null, "regex should still match the safe prefix");
+  assert.equal(match[0], "http://x.com", "match stops before the single-quote");
+});
+
+test("AUTO_LINK_RE matches a normal URL (5a — not a regression)", () => {
+  var url = "https://example.com/path?q=1&r=2#anchor";
+  AUTO_LINK_RE.lastIndex = 0;
+  var match = AUTO_LINK_RE.exec(url);
+  assert.ok(match !== null, "normal URL should match");
+  assert.equal(match[0], url, "entire normal URL is matched");
+});
+
+// ============================================================
+// 5a — fmt() end-to-end: attack payload does not produce href breakout
+// ============================================================
+
+test("fmt: attack URL with double-quote does not inject event handler (5a)", () => {
+  // The stored XSS payload: note text containing a URL with embedded double-quote.
+  // Before the fix: produced <a href="http://x.com"onmouseover="alert(1)"...>
+  // After the fix:  the URL match stops at the double-quote; the rest is
+  //                 rendered as escaped text, not an attribute.
+  var note = 'http://x.com"onmouseover="alert(1)';
+  var out = fmt(note);
+
+  // Must contain an anchor for the safe prefix only.
+  assert.ok(out.includes('<a href="http://x.com"'), "safe prefix is linked");
+
+  // Must not produce a bare onmouseover= attribute on the anchor.
+  // The injected string must appear HTML-escaped, not raw.
+  assert.ok(!out.includes('" onmouseover='), "no injected attribute (space variant)");
+  assert.ok(!out.includes('"onmouseover='), "no injected attribute (no-space variant)");
+});
+
+test("fmt: attack URL with single-quote does not inject event handler (5a)", () => {
+  var note = "http://x.com'onmouseover='alert(1)";
+  var out = fmt(note);
+
+  assert.ok(out.includes('<a href="http://x.com"'), "safe prefix is linked");
+  assert.ok(!out.includes("' onmouseover="), "no injected attribute (space variant)");
+  assert.ok(!out.includes("'onmouseover="), "no injected attribute (no-space variant)");
+});
+
+test("fmt: normal URL is auto-linked without modification (5a — not a regression)", () => {
+  var url = "https://example.com/path";
+  var out = fmt(url);
+  assert.ok(
+    out.includes('<a href="https://example.com/path" target="_blank" rel="noopener">'),
+    "normal URL is wrapped in anchor with correct attributes"
+  );
+});
+
+test("fmt: plain text with no URL is returned HTML-escaped (no anchors)", () => {
+  var out = fmt("hello <world> & friends");
+  assert.equal(out, "hello &lt;world&gt; &amp; friends");
+  assert.ok(!out.includes("<a"), "no anchor for plain text");
+});