From 1cf4975d2f6fc58d148561c1e682eb8667bf1c55 Mon Sep 17 00:00:00 2001
From: James Russo <james.russo@heygen.com>
Date: Thu, 22 Oct 2026 21:31:43 +0000
Subject: [PATCH] fix(parsers): preserve Unicode offsets when stamping IDs
 (#6079)

---
 packages/parsers/src/hfIds.test.ts |  8 ++++++++
 packages/parsers/src/hfIds.ts      | 18 +++++-------------
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/packages/parsers/src/hfIds.test.ts b/packages/parsers/src/hfIds.test.ts
index 5f120f49d5..662aec881f 100644
--- a/packages/parsers/src/hfIds.test.ts
+++ b/packages/parsers/src/hfIds.test.ts
@@ -44,6 +44,14 @@ describe("ensureHfIds fragment detection", () => {
 });
 
 describe("stampHfIdsInPlace keeps the source's own formatting", () => {
+  it.each(["script", "style"])("keeps source offsets after expanding Unicode near %s", (tag) => {
+    const html = `<div DATA-X='KeepCase'>${"İ".repeat(20)}<${tag}>/* İ <span> */</${tag.toUpperCase()} \n><p class='KeepMe'>after</p></div>`;
+    const out = stampHfIdsInPlace(html);
+    expect(out.replace(/ data-hf-id="hf-[a-z0-9]{4}"/g, "")).toBe(html);
+    expect(ids(out)).toEqual(ids(ensureHfIds(html)));
+    expect(stampHfIdsInPlace(out)).toBe(out);
+  });
+
   it("only inserts ids into a composition written without whitespace", () => {
     const html =
       '<template id="s-template"><div data-composition-id="s" data-start="0" data-duration="4"><style>#t{color:red}</style><img src="a.png"/><input disabled><p class=\'t\' id=t>Hi<br></p></div></template>';
diff --git a/packages/parsers/src/hfIds.ts b/packages/parsers/src/hfIds.ts
index 6aa2f30645..52e23db83d 100644
--- a/packages/parsers/src/hfIds.ts
+++ b/packages/parsers/src/hfIds.ts
@@ -62,7 +62,6 @@ const IMPLIED = new Set(["html", "head", "body", "tbody"]);
 type StartTag = { name: string; nameEnd: number; bracket: number };
 
 function startTags(html: string): StartTag[] | null {
-  const lower = html.toLowerCase();
   const tags: StartTag[] = [];
   let i = html.indexOf("<");
   while (i >= 0) {
@@ -77,23 +76,16 @@ function startTags(html: string): StartTag[] | null {
     if (end < 0) return null;
     const tag = name[1]!.toLowerCase();
     tags.push({ name: tag, nameEnd: i + name[0].length, bracket: end });
-    const after = RAW_TEXT.has(tag) ? rawTextEnd(lower, tag, end) : end;
+    const after = RAW_TEXT.has(tag) ? rawTextEnd(html, tag, end) : end;
     i = after < 0 ? -1 : html.indexOf("<", after + 1);
   }
   return tags;
 }
 
-function rawTextEnd(lower: string, tag: string, from: number): number {
-  const marker = `</${tag}`;
-  for (
-    let at = lower.indexOf(marker, from);
-    at >= 0;
-    at = lower.indexOf(marker, at + marker.length)
-  ) {
-    const next = lower[at + marker.length];
-    if (next !== undefined && /[\s/>]/.test(next)) return at;
-  }
-  return -1;
+function rawTextEnd(html: string, tag: string, from: number): number {
+  const endTag = new RegExp(`</${tag}(?=[\\s/>]|$)`, "gi");
+  endTag.lastIndex = from;
+  return endTag.exec(html)?.index ?? -1;
 }
 
 function nextTagAfter(html: string, lt: number): number {