diff --git a/packages/core/src/compiler/htmlDocument.test.ts b/packages/core/src/compiler/htmlDocument.test.ts
index 615fd6c66c..3f1138e453 100644
--- a/packages/core/src/compiler/htmlDocument.test.ts
+++ b/packages/core/src/compiler/htmlDocument.test.ts
@@ -5,6 +5,7 @@ import {
   injectScriptsIntoHtml,
   injectTagsAtHeadStart,
   insertBeforeCloseTag,
+  hasCompositionOutsideTemplates,
   isFullHtmlDocument,
   parseHTMLContent,
   stripEmbeddedRuntimeScripts,
@@ -272,3 +273,47 @@ describe("injectTagsAtHeadStart on long adversarial input", () => {
     expect(performance.now() - started).toBeLessThan(1500);
   });
 });
+
+describe("hasCompositionOutsideTemplates", () => {
+  it.each([
+    ["a root in <body>", '<body><div data-composition-id="main"></div></body>', true],
+    [
+      "a root in <body> beside an inline template",
+      '<body><div data-composition-id="main"></div><template><div data-composition-id="x"></div></template></body>',
+      true,
+    ],
+    [
+      "a full document whose composition is in its template",
+      '<html><body><template id="s-template"><div data-composition-id="s"></div></template></body></html>',
+      false,
+    ],
+    ["a bare template", '<template><div data-composition-id="s"></div></template>', false],
+    [
+      "an id on <html> and on the <template> tag itself",
+      '<html data-composition-id="s"><body><template data-composition-id="s"><div></div></template></body></html>',
+      false,
+    ],
+    [
+      "a root id on <html> beside a template with no composition",
+      '<html data-composition-id="main"><body><template><p>clone me</p></template></body></html>',
+      true,
+    ],
+    [
+      "a full document whose <html> carries the id",
+      '<html data-composition-id="s"><body data-composition-id="s"><template><div data-composition-id="s"></div></template></body></html>',
+      false,
+    ],
+    [
+      "the attribute only in a comment or text",
+      '<body><!-- <div data-composition-id="a"> --><p>data-composition-id="b"</p></body>',
+      false,
+    ],
+    [
+      "a nested template",
+      '<template><template></template><div data-composition-id="s"></div></template>',
+      false,
+    ],
+  ])("%s", (_name, html, expected) => {
+    expect(hasCompositionOutsideTemplates(html)).toBe(expected);
+  });
+});
diff --git a/packages/core/src/compiler/htmlDocument.ts b/packages/core/src/compiler/htmlDocument.ts
index cf98279623..579b1e0aa4 100644
--- a/packages/core/src/compiler/htmlDocument.ts
+++ b/packages/core/src/compiler/htmlDocument.ts
@@ -300,6 +300,35 @@ function findOuterTemplateClose(html: string): number {
   return -1;
 }
 
+const COMPOSITION_ID_ATTR = /\sdata-composition-id\s*=/;
+
+const isDocumentWrapper = (lowered: string, open: number): boolean =>
+  isTagAt(lowered, open, "<html") || isTagAt(lowered, open, "<body");
+
+function carriesCompositionId(lowered: string, open: number): boolean {
+  const end = findTagEnd(lowered, open + 1);
+  return end !== -1 && COMPOSITION_ID_ATTR.test(lowered.slice(open, end));
+}
+
+export function hasCompositionOutsideTemplates(html: string): boolean {
+  const lowered = lowerAscii(html);
+  let depth = 0;
+  let idOnWrapper = false;
+  let idInTemplate = false;
+  for (const open of markupStarts(lowered)) {
+    if (isTagAt(lowered, open, "<template")) {
+      depth++;
+      if (carriesCompositionId(lowered, open)) idInTemplate = true;
+    } else if (isTagAt(lowered, open, "</template")) depth = Math.max(0, depth - 1);
+    else if (/[a-z]/.test(lowered.charAt(open + 1)) && carriesCompositionId(lowered, open)) {
+      if (depth > 0) idInTemplate = true;
+      else if (isDocumentWrapper(lowered, open)) idOnWrapper = true;
+      else return true;
+    }
+  }
+  return idOnWrapper && !idInTemplate;
+}
+
 function insertBeforeDocumentTag(html: string, tag: DocumentTag, markup: string): string | null {
   const at = tag === "</template" ? findOuterTemplateClose(html) : findDocumentTag(html, tag);
   return at === -1 ? null : html.slice(0, at) + markup + html.slice(at);
diff --git a/packages/studio-server/src/routes/files.test.ts b/packages/studio-server/src/routes/files.test.ts
index f6b33b1b11..50315bea52 100644
--- a/packages/studio-server/src/routes/files.test.ts
+++ b/packages/studio-server/src/routes/files.test.ts
@@ -1949,11 +1949,40 @@ const tl = gsap.timeline({ paused: true });
     expect(html).not.toContain("<body");
   });
 
-  it("a first animation in a <body> file lands before </body>, outside its template", async () => {
+  // The registry-block shape: the loader mounts the template's content, so a script outside it never runs.
+  it("a first animation in a full-document sub-composition lands inside its template", async () => {
     const html = await addFirstAnimation(
-      '<body><template><div data-composition-id="sub"><div id="card"></div></div></template></body>\n',
+      '<!DOCTYPE html><html><head><meta charset="utf-8"></head><body><template id="sub-template"><div data-composition-id="sub"><div id="card"></div></div></template></body></html>\n',
     );
-    expect(html.indexOf("<script")).toBeGreaterThan(html.indexOf("</template>"));
+    const close = html.indexOf("</template>");
+    expect(html.indexOf('window.__timelines["sub"]')).toBeGreaterThan(-1);
+    expect(html.lastIndexOf("</script>")).toBeLessThan(close);
+    expect(html.slice(close)).toBe("</template></body></html>\n");
+  });
+
+  it("a first animation lands inside the template when <html> carries the composition id", async () => {
+    const html = await addFirstAnimation(
+      '<!DOCTYPE html><html data-composition-id="sub"><body><template><div data-composition-id="sub"><div id="card"></div></div></template></body></html>\n',
+    );
+    const close = html.indexOf("</template>");
+    expect(html.lastIndexOf("</script>")).toBeLessThan(close);
+    expect(html.slice(close)).toBe("</template></body></html>\n");
+  });
+
+  it("a first animation lands inside the template when the <template> tag carries the composition id", async () => {
+    const html = await addFirstAnimation(
+      '<!DOCTYPE html><html data-composition-id="sub"><body><template data-composition-id="sub"><div id="card"></div></template></body></html>\n',
+    );
+    const close = html.indexOf("</template>");
+    expect(html.lastIndexOf("</script>")).toBeLessThan(close);
+    expect(html.slice(close)).toBe("</template></body></html>\n");
+  });
+
+  it("a first animation in a file whose composition is in <body> lands before </body>", async () => {
+    const html = await addFirstAnimation(
+      '<body><div data-composition-id="main"><div id="card"></div></div><template id="other-template"><div data-composition-id="other"></div></template></body>\n',
+    );
+    expect(html.indexOf('window.__timelines["main"]')).toBeGreaterThan(html.indexOf("</template>"));
     expect(html.lastIndexOf("</script>")).toBeLessThan(html.indexOf("</body>"));
   });
 
diff --git a/packages/studio-server/src/routes/files.ts b/packages/studio-server/src/routes/files.ts
index afc7f2e03a..03476dc847 100644
--- a/packages/studio-server/src/routes/files.ts
+++ b/packages/studio-server/src/routes/files.ts
@@ -105,7 +105,10 @@ import {
 } from "../helpers/compositionInsertion.js";
 import { resolveGsapWriter } from "./gsapMutationCapabilities.js";
 import { requestSubPath } from "../helpers/requestSubPath.js";
-import { insertBeforeCloseTag } from "@hyperframes/core/compiler/html-document";
+import {
+  hasCompositionOutsideTemplates,
+  insertBeforeCloseTag,
+} from "@hyperframes/core/compiler/html-document";
 
 // ── Server cutover flag ─────────────────────────────────────────────────────
 
@@ -1457,9 +1460,12 @@ async function prepareGsapMutationScript(
       `window.__timelines["${compId}"] = tl;`,
       "</script>",
     ].join("\n");
+    const [first, second] = hasCompositionOutsideTemplates(html)
+      ? (["body", "template"] as const)
+      : (["template", "body"] as const);
     html =
-      insertBeforeCloseTag(html, "body", `${bootstrap}\n`) ??
-      insertBeforeCloseTag(html, "template", `${bootstrap}\n`) ??
+      insertBeforeCloseTag(html, first, `${bootstrap}\n`) ??
+      insertBeforeCloseTag(html, second, `${bootstrap}\n`) ??
       `${html}\n${bootstrap}`;
     block = extractGsapScriptBlock(html);
   }