diff --git a/crates/rustmotion-html/src/lib.rs b/crates/rustmotion-html/src/lib.rs
index 69d9ea43..a5a788bb 100644
--- a/crates/rustmotion-html/src/lib.rs
+++ b/crates/rustmotion-html/src/lib.rs
@@ -401,7 +401,7 @@ pub fn set_inline_style(html: &str, pointer: &str, prop: &str, value: &str) -> O
     let root = find_element(&dom.document, "rustmotion")?;
     let target = resolve_pointer(&root, pointer)?;
     set_style_attr(&target, prop, value)?;
-    Some(serialize_element(&root))
+    splice_rustmotion_subtree(html, &root)
 }
 
 /// Replace the text content of the element addressed by the JSON pointer with
@@ -413,7 +413,7 @@ pub fn set_text_content(html: &str, pointer: &str, text: &str) -> Option<String>
     let root = find_element(&dom.document, "rustmotion")?;
     let target = resolve_pointer(&root, pointer)?;
     set_text(&target, text)?;
-    Some(serialize_element(&root))
+    splice_rustmotion_subtree(html, &root)
 }
 
 /// Set or replace a plain attribute on the element addressed by the JSON
@@ -429,7 +429,7 @@ pub fn set_attribute(html: &str, pointer: &str, name: &str, value: &str) -> Opti
     let root = find_element(&dom.document, "rustmotion")?;
     let target = resolve_pointer(&root, pointer)?;
     set_attr(&target, name, value)?;
-    Some(serialize_element(&root))
+    splice_rustmotion_subtree(html, &root)
 }
 
 /// Remove one inline `style` property from the element addressed by the JSON
@@ -441,7 +441,7 @@ pub fn remove_inline_style(html: &str, pointer: &str, prop: &str) -> Option<Stri
     let root = find_element(&dom.document, "rustmotion")?;
     let target = resolve_pointer(&root, pointer)?;
     remove_style_decl(&target, prop)?;
-    Some(serialize_element(&root))
+    splice_rustmotion_subtree(html, &root)
 }
 
 /// Upsert (or, for an empty value, remove) a plain attribute on an element.
@@ -600,15 +600,42 @@ fn upsert_decl(decls: &str, prop: &str, value: &str) -> String {
         .join("; ")
 }
 
-fn serialize_element(handle: &Handle) -> String {
+/// Re-serialize `root` (the mutated `<rustmotion>` subtree) and splice it
+/// back into `original` at the exact byte span its `<rustmotion>...
+/// </rustmotion>` element occupies there, leaving everything before and
+/// after — doctype, `<head>`, comments, anything else the author wrote —
+/// byte-for-byte untouched. `original` is used as the source of truth for
+/// that surrounding content rather than `root`'s own parsed document,
+/// because `parse_fragment_dom` parses in a body-fragment context, which
+/// does not retain a doctype at all and does not guarantee round-tripping
+/// `<html>`/`<head>`/`<body>` the way the author wrote them. Refuses
+/// (`None`) rather than write a corrupted file when the span can't be
+/// located (no `<rustmotion>`/`</rustmotion>` literal in `original`, e.g. an
+/// unclosed root) or the serializer itself fails.
+fn splice_rustmotion_subtree(original: &str, root: &Handle) -> Option<String> {
+    let open_start = original.find("<rustmotion")?;
+    let close_start = original.rfind("</rustmotion")?;
+    let close_end = close_start + original[close_start..].find('>')? + 1;
+    if close_end <= open_start {
+        return None;
+    }
+    let serialized = serialize_element(root).ok()?;
+    let mut out = String::with_capacity(original.len() + serialized.len());
+    out.push_str(&original[..open_start]);
+    out.push_str(&serialized);
+    out.push_str(&original[close_end..]);
+    Some(out)
+}
+
+fn serialize_element(handle: &Handle) -> Result<String, HtmlError> {
     let mut buf = Vec::new();
     let node: SerializableHandle = handle.clone().into();
     let opts = SerializeOpts {
         traversal_scope: TraversalScope::IncludeNode,
         ..Default::default()
     };
-    let _ = serialize(&mut buf, &node, opts);
-    String::from_utf8(buf).unwrap_or_default()
+    serialize(&mut buf, &node, opts).map_err(|e| HtmlError::SerializeFailed(e.to_string()))?;
+    String::from_utf8(buf).map_err(|e| HtmlError::SerializeFailed(e.to_string()))
 }
 
 #[cfg(test)]
diff --git a/crates/rustmotion-html/tests/audit_ws_f.rs b/crates/rustmotion-html/tests/audit_ws_f.rs
index 26165420..e8ab981a 100644
--- a/crates/rustmotion-html/tests/audit_ws_f.rs
+++ b/crates/rustmotion-html/tests/audit_ws_f.rs
@@ -263,3 +263,79 @@ fn inline_formatting_tags_still_flatten_into_the_parent_text() {
         json!("Real bold text")
     );
 }
+
+// ---------------------------------------------------------------------------
+// studio HTML write-back silently deletes everything outside
+// <rustmotion> in the author's file.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn write_back_preserves_doctype_head_and_surrounding_comments() {
+    let html = concat!(
+        "<!DOCTYPE html>\n",
+        "<html><head><meta charset=\"utf-8\"></head><body>\n",
+        "<!-- authored by hand -->\n",
+        "<rustmotion width=\"100\" height=\"100\"><scene duration=\"2\">",
+        "<h1 style=\"font-size:96\">Hi</h1></scene></rustmotion>\n",
+        "<!-- trailing note -->\n",
+        "</body></html>\n",
+    );
+    let out = rustmotion_html::set_inline_style(html, "/scenes/0/children/0", "font-size", "120")
+        .expect("pointer resolves");
+    assert!(
+        out.contains("<!DOCTYPE html>"),
+        "doctype must survive: {out}"
+    );
+    assert!(
+        out.contains("<meta charset=\"utf-8\">"),
+        "head must survive: {out}"
+    );
+    assert!(
+        out.contains("<!-- authored by hand -->"),
+        "leading comment must survive: {out}"
+    );
+    assert!(
+        out.contains("<!-- trailing note -->"),
+        "trailing comment must survive: {out}"
+    );
+    assert!(
+        out.contains("font-size:120"),
+        "the edit itself must still apply: {out}"
+    );
+    let v = html_to_scenario_value(&out).expect("round-trips through the transpiler");
+    assert_eq!(
+        v["scenes"][0]["children"][0]["style"]["font-size"],
+        json!(120)
+    );
+}
+
+#[test]
+fn write_back_via_set_text_content_also_preserves_surrounding_document() {
+    let html = concat!(
+        "<!DOCTYPE html>\n",
+        "<!-- keep me -->\n",
+        "<rustmotion width=\"100\" height=\"100\"><scene duration=\"2\">",
+        "<h1>Hi</h1></scene></rustmotion>\n",
+        "<!-- keep me too -->\n",
+    );
+    let out = rustmotion_html::set_text_content(html, "/scenes/0/children/0", "Bonjour")
+        .expect("pointer resolves");
+    assert!(
+        out.contains("<!DOCTYPE html>"),
+        "doctype must survive: {out}"
+    );
+    assert!(out.contains("<!-- keep me -->"), "got: {out}");
+    assert!(out.contains("<!-- keep me too -->"), "got: {out}");
+    let v = html_to_scenario_value(&out).expect("round-trips through the transpiler");
+    assert_eq!(v["scenes"][0]["children"][0]["content"], json!("Bonjour"));
+}
+
+#[test]
+fn write_back_refuses_when_the_closing_tag_cannot_be_located_in_source() {
+    let html = r##"<rustmotion width="100" height="100"><scene duration="2"><h1 style="font-size:96">Hi</h1></scene>"##;
+    let out = rustmotion_html::set_inline_style(html, "/scenes/0/children/0", "font-size", "120");
+    assert!(
+        out.is_none(),
+        "must refuse rather than write a file it cannot faithfully reconstruct"
+    );
+}