diff --git a/packages/core/src/runtime/init.test.ts b/packages/core/src/runtime/init.test.ts
index 5cf42e2fb3..c0b68ca4d7 100644
--- a/packages/core/src/runtime/init.test.ts
+++ b/packages/core/src/runtime/init.test.ts
@@ -2,6 +2,12 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import { readFileSync } from "node:fs";
 import { initSandboxRuntimeModular, installFlatGsapTransforms } from "./init";
+import {
+  hideTimedClipsUntilFirstPass,
+  revealTimedClipsAfterFirstPass,
+  SKIPPED_CLIP,
+} from "./timedClipHide";
+import { applyAuthoredTiming, STUDIO_PREVIEW_MARK_META } from "../studioPreviewMark";
 import { collectRuntimeTimelinePayload } from "./timeline";
 import { TYPEGPU_PRESENT_HEARTBEAT_MS } from "./adapters/typegpu";
 import { WebAudioTransport } from "./webAudioTransport";
@@ -360,6 +366,154 @@ describe("initSandboxRuntimeModular", () => {
     expect(caption.getAttribute("data-start")).toBe("0");
   });
 
+  describe("visibility of runtime-stamped elements in Studio preview", () => {
+    afterEach(() => vi.restoreAllMocks());
+
+    // A 10 s film: a video clip, an untimed full-frame backdrop the composition's per-frame script
+    // shows only from 6 s to 8 s, and an untimed badge it never touches. Driven by real GSAP.
+    const mountFilm = () => {
+      const raf = createManualRaf();
+      vi.spyOn(performance, "now").mockImplementation(() => raf.now());
+      window.requestAnimationFrame =
+        raf.requestAnimationFrame as typeof window.requestAnimationFrame;
+      window.cancelAnimationFrame = raf.cancelAnimationFrame as typeof window.cancelAnimationFrame;
+      document.body.innerHTML =
+        `<div id="root" data-composition-id="main" data-root="true" data-start="0" data-duration="10" data-width="1080" data-height="1920">` +
+        `<video id="aroll" class="clip" data-start="0" data-duration="10" muted></video>` +
+        `<div id="plate" style="visibility: hidden"></div>` +
+        `<div id="badge"></div>` +
+        `</div>`;
+      const video = document.querySelector("video")!;
+      video.play = vi.fn(() => Promise.resolve());
+      video.pause = vi.fn();
+      video.load = vi.fn();
+      const plate = document.getElementById("plate")!;
+      const tl = gsap.timeline({ paused: true });
+      const frame = { t: 0 };
+      tl.to(frame, {
+        t: 10,
+        duration: 10,
+        ease: "none",
+        modifiers: {
+          t: (value: number) => {
+            plate.style.visibility = value >= 6 && value < 8 ? "visible" : "hidden";
+            return value;
+          },
+        },
+      });
+      window.__timelines = { main: tl as unknown as RuntimeTimelineLike };
+      withStudioIframe(() => initSandboxRuntimeModular());
+      return { raf, plate, badge: document.getElementById("badge")! };
+    };
+
+    it("keeps a stamped backdrop its script hides hidden on every playing tick", () => {
+      const { raf, plate } = mountFilm();
+      expect(plate.getAttribute("data-hf-autostamped")).toBe("1");
+
+      window.__player?.seek(1);
+      window.__player?.play();
+      const seen = new Set<string>();
+      for (let frame = 0; frame < 120; frame++) {
+        raf.step(16);
+        seen.add(plate.style.visibility);
+      }
+
+      expect(window.__player?.getTime()).toBeGreaterThan(2.5);
+      expect(window.__player?.getTime()).toBeLessThan(6);
+      expect([...seen]).toEqual(["hidden"]);
+    });
+
+    it("still shows a stamped element its author never hides", () => {
+      const { raf, badge } = mountFilm();
+      expect(badge.getAttribute("data-hf-autostamped")).toBe("1");
+
+      window.__player?.seek(1);
+      window.__player?.play();
+      for (let frame = 0; frame < 30; frame++) raf.step(16);
+
+      expect(badge.style.visibility).not.toBe("hidden");
+      expect(getComputedStyle(badge).visibility).toBe("visible");
+    });
+
+    it("hides an authored clip inside a hidden authored clip under a stamped wrapper", () => {
+      document.body.innerHTML =
+        `<div data-composition-id="main" data-root="true" data-start="0" data-duration="10" data-width="1080" data-height="1920">` +
+        `<div id="wall"><div id="scene" data-start="0" data-duration="2">` +
+        `<div id="card" data-start="0" data-duration="10"></div></div></div>` +
+        `</div>`;
+      window.__timelines = { main: createMockTimeline(10) };
+      withStudioIframe(() => initSandboxRuntimeModular());
+      const wall = document.getElementById("wall")!;
+      const scene = document.getElementById("scene")!;
+      const card = document.getElementById("card")!;
+      expect(wall.getAttribute("data-hf-autostamped")).toBe("1");
+
+      window.__player?.renderSeek(1);
+      expect([scene.style.visibility, card.style.visibility]).toEqual(["visible", "visible"]);
+
+      window.__player?.renderSeek(5);
+      expect([scene.style.visibility, card.style.visibility]).toEqual(["hidden", "hidden"]);
+    });
+
+    it("hides a stamped element Studio re-times outside its new window", () => {
+      document.body.innerHTML =
+        `<div data-composition-id="main" data-root="true" data-start="0" data-duration="10" data-width="1080" data-height="1920">` +
+        `<div id="title" style="position: absolute"></div>` +
+        `</div>`;
+      window.__timelines = { main: createMockTimeline(10) };
+      withStudioIframe(() => initSandboxRuntimeModular());
+      const title = document.getElementById("title")!;
+      expect(title.getAttribute("data-hf-autostamped")).toBe("1");
+
+      applyAuthoredTiming(title, [
+        ["data-start", "4"],
+        ["data-duration", "2"],
+      ]);
+      (window as Window & { __hfForceTimelineRebind?: () => void }).__hfForceTimelineRebind?.();
+
+      const at = (time: number) => {
+        window.__player?.renderSeek(time);
+        return title.style.visibility;
+      };
+      expect([at(1), at(5), at(8)]).toEqual(["hidden", "visible", "hidden"]);
+    });
+
+    it("times a clip by its window in a render even when its source carries the stamp", () => {
+      document.body.innerHTML =
+        `<div data-composition-id="main" data-root="true" data-start="0" data-duration="10" data-width="1080" data-height="1920">` +
+        `<div id="title" style="position: absolute" data-start="5" data-duration="2" data-hf-autostamped="1"></div>` +
+        `</div>`;
+      window.__timelines = { main: createMockTimeline(10) };
+      initSandboxRuntimeModular();
+      const title = document.getElementById("title")!;
+
+      const at = (time: number) => {
+        window.__player?.renderSeek(time);
+        return title.style.visibility;
+      };
+      expect([at(1), at(6), at(9)]).toEqual(["hidden", "visible", "hidden"]);
+    });
+
+    it("does not hold a paused seek on images in a stamped container its script hides", () => {
+      const mark = Object.assign(document.createElement("meta"), {
+        name: STUDIO_PREVIEW_MARK_META,
+      });
+      document.head.append(mark);
+      try {
+        hideTimedClipsUntilFirstPass();
+        const { plate } = mountFilm();
+        plate.append(Object.assign(document.createElement("img"), { src: "backdrop.png" }));
+
+        expect(plate.matches(SKIPPED_CLIP)).toBe(false);
+        expect(window.__player?.seek(1)).toBeUndefined();
+      } finally {
+        mark.remove();
+        revealTimedClipsAfterFirstPass();
+        document.head.querySelector("style[data-hf-skip-hidden-images]")?.remove();
+      }
+    });
+  });
+
   /**
    * GH#4001: a root edited to portrait dims whose scaffolded `html, body` CSS
    * is left at the old landscape size renders successfully with everything
diff --git a/packages/core/src/runtime/init.ts b/packages/core/src/runtime/init.ts
index 62d4894495..295c0a3548 100644
--- a/packages/core/src/runtime/init.ts
+++ b/packages/core/src/runtime/init.ts
@@ -9,6 +9,7 @@ import { isInClipWindow } from "./clipWindow";
 import { revealTimedClipsAfterFirstPass, SKIPPED_CLIP, skipsHiddenImages } from "./timedClipHide";
 import {
   PREVIEW_ONLY_ATTRS,
+  RUNTIME_STAMPED_ATTR,
   STUDIO_PREVIEW_LAZY_ATTR,
   STUDIO_PREVIEW_UPCOMING_ATTR,
 } from "../studioPreviewMark";
@@ -409,6 +410,7 @@ function loadPreviewImagesIn(root: Element): void {
 
 export function initSandboxRuntimeModular(): void {
   const state = createRuntimeState();
+  const stampsForStudio = window.parent !== window;
   authoredMediaObserver?.disconnect();
   authoredMediaObserver = null;
   if (readSceneParts(document)) recordAuthoredMedia(document.documentElement);
@@ -834,7 +836,7 @@ export function initSandboxRuntimeModular(): void {
       // `justify-content: space-between` clusters in the top-left. Leave them in
       // flow so the preview matches the rendered video, which never stamps
       // (production renders run as the top-level page, not in an iframe).
-      return !el.hasAttribute("data-hf-autostamped");
+      return !el.hasAttribute(RUNTIME_STAMPED_ATTR);
     });
     const displayNoneLiftedToMeasureShown = clips
       .filter((el) => el.style.getPropertyValue("display") === "none")
@@ -2012,7 +2014,7 @@ export function initSandboxRuntimeModular(): void {
     // them so the Studio timeline can discover individual animated elements.
     // Only when embedded in an iframe (Studio preview) — production renders
     // run as the top-level page and must not mutate element timing.
-    if (window.parent !== window) {
+    if (stampsForStudio) {
       const rootComp = resolveRootCompositionElement();
       const rootDuration = boundDuration > 0 ? boundDuration : 0;
       const dur = String(rootDuration > 0 ? rootDuration : 1);
@@ -2058,7 +2060,7 @@ export function initSandboxRuntimeModular(): void {
               target.setAttribute("data-duration", dur);
               // Mark as runtime-stamped so applyClipLayout leaves it in document
               // flow instead of treating it as an authored overlay clip.
-              target.setAttribute("data-hf-autostamped", "1");
+              target.setAttribute(RUNTIME_STAMPED_ATTR, "1");
             }
           }
         } catch {
@@ -2083,7 +2085,7 @@ export function initSandboxRuntimeModular(): void {
           el.setAttribute("data-duration", dur);
           // Mark as runtime-stamped so applyClipLayout leaves it in document
           // flow instead of treating it as an authored overlay clip.
-          el.setAttribute("data-hf-autostamped", "1");
+          el.setAttribute(RUNTIME_STAMPED_ATTR, "1");
         }
       }
     }
@@ -2818,7 +2820,8 @@ export function initSandboxRuntimeModular(): void {
       const isVisibleNow =
         visibleAt(rawNode, currentTime) &&
         clipChainVisibleAt(rawNode.parentElement, currentTime, visibleAt, rootComp);
-      rawNode.style.visibility = isVisibleNow ? "visible" : "hidden";
+      const isRuntimeStamped = stampsForStudio && rawNode.hasAttribute(RUNTIME_STAMPED_ATTR);
+      if (!isRuntimeStamped) rawNode.style.visibility = isVisibleNow ? "visible" : "hidden";
       const upcoming =
         hiddenImagesSkipped && !isVisibleNow && dueSoon(rawNode, visibleAt, currentTime);
       if (upcoming && !rawNode.hasAttribute(STUDIO_PREVIEW_UPCOMING_ATTR))
@@ -2877,7 +2880,9 @@ export function initSandboxRuntimeModular(): void {
       const visibleAt = timedVisibilityAt();
       return Array.from(document.images).filter(
         (img) =>
-          img.closest('[data-start][style*="visibility: hidden"]') !== null &&
+          img.closest(
+            `[data-start]:not([${RUNTIME_STAMPED_ATTR}])[style*="visibility: hidden"]`,
+          ) !== null &&
           (img.closest(SKIPPED_CLIP) !== null || !img.complete) &&
           clipChainVisibleAt(img, time, visibleAt, rootComp),
       );
diff --git a/packages/core/src/runtime/timedClipHide.ts b/packages/core/src/runtime/timedClipHide.ts
index 38e14c35cf..37e91a4822 100644
--- a/packages/core/src/runtime/timedClipHide.ts
+++ b/packages/core/src/runtime/timedClipHide.ts
@@ -1,4 +1,8 @@
-import { STUDIO_PREVIEW_MARK_META, STUDIO_PREVIEW_UPCOMING_ATTR } from "../studioPreviewMark";
+import {
+  RUNTIME_STAMPED_ATTR,
+  STUDIO_PREVIEW_MARK_META,
+  STUDIO_PREVIEW_UPCOMING_ATTR,
+} from "../studioPreviewMark";
 
 // Hides timed non-media clips from script evaluation until the first visibility pass decides them;
 // before it, a paused page painted every clip at once. Media is left to init's media pass.
@@ -8,7 +12,7 @@ const HIDE_UNTIL_FIRST_PASS =
   "[data-start]:not(video, audio, img) { visibility: hidden !important; }";
 const PREVIEW_HIDE_UNTIL_FIRST_PASS = 'img[loading="lazy"] { display: none !important; }';
 const SKIP_ATTR = "data-hf-skip-hidden-images";
-export const SKIPPED_CLIP = `[data-start]:not(video, audio, img, [${STUDIO_PREVIEW_UPCOMING_ATTR}])[style*="visibility: hidden"]`;
+export const SKIPPED_CLIP = `[data-start]:not(video, audio, img, [${STUDIO_PREVIEW_UPCOMING_ATTR}], [${RUNTIME_STAMPED_ATTR}])[style*="visibility: hidden"]`;
 const SKIP_HIDDEN_IMAGES = `${SKIPPED_CLIP} img { display: none !important; }`;
 const STUDIO_PREVIEW_MARK = `meta[name="${STUDIO_PREVIEW_MARK_META}"]`;
 
diff --git a/packages/core/src/studioPreviewMark.ts b/packages/core/src/studioPreviewMark.ts
index 58dec41377..e885cd6aff 100644
--- a/packages/core/src/studioPreviewMark.ts
+++ b/packages/core/src/studioPreviewMark.ts
@@ -3,8 +3,18 @@ export const STUDIO_PREVIEW_UPCOMING_ATTR = "data-hf-upcoming";
 export const STUDIO_PREVIEW_LAZY_ATTR = "data-hf-preview-lazy";
 export const STUDIO_PREVIEW_ERRORS = "__hfPreviewErrors";
 export const PREVIEW_RASTER_ATTR = "data-hf-preview-raster";
+export const RUNTIME_STAMPED_ATTR = "data-hf-autostamped";
 export const PREVIEW_ONLY_ATTRS = [
   STUDIO_PREVIEW_UPCOMING_ATTR,
   STUDIO_PREVIEW_LAZY_ATTR,
   PREVIEW_RASTER_ATTR,
+  RUNTIME_STAMPED_ATTR,
 ] as const;
+
+export function applyAuthoredTiming(
+  el: Element,
+  attrs: ReadonlyArray<readonly [name: string, value: string]>,
+): void {
+  for (const [name, value] of attrs) el.setAttribute(name, value);
+  el.removeAttribute(RUNTIME_STAMPED_ATTR);
+}
diff --git a/packages/studio/src/hooks/timelineEditingHelpers.test.ts b/packages/studio/src/hooks/timelineEditingHelpers.test.ts
index a912e3e81b..5532dab252 100644
--- a/packages/studio/src/hooks/timelineEditingHelpers.test.ts
+++ b/packages/studio/src/hooks/timelineEditingHelpers.test.ts
@@ -218,6 +218,26 @@ describe("patchIframeDomTiming", () => {
 
     expect([...cards!].map((card) => card.dataset.start)).toEqual(["1", "9"]);
   });
+
+  it("makes a runtime-stamped element authored on any timing edit, a lane move included", () => {
+    const iframe = makeIframeWith(`
+      <div data-composition-id="root">
+        <div id="title" data-start="0" data-duration="10" data-hf-autostamped="1"></div>
+        <div id="badge" data-start="0" data-duration="10" data-hf-autostamped="1"></div>
+      </div>
+    `);
+    const doc = iframe.contentDocument!;
+    const at = (id: string) => el({ id, tag: "div", domId: id, sourceFile: "index.html" });
+
+    patchIframeDomTiming(iframe, at("title"), [
+      ["data-start", "4"],
+      ["data-duration", "2"],
+    ]);
+    patchIframeDomTiming(iframe, at("badge"), [["data-track-index", "3"]]);
+
+    expect(doc.getElementById("title")?.hasAttribute("data-hf-autostamped")).toBe(false);
+    expect(doc.getElementById("badge")?.hasAttribute("data-hf-autostamped")).toBe(false);
+  });
 });
 
 describe("extendRootDurationIfNeeded", () => {
diff --git a/packages/studio/src/hooks/timelineEditingHelpers.ts b/packages/studio/src/hooks/timelineEditingHelpers.ts
index dbfdd8fdfa..74f9b84d9a 100644
--- a/packages/studio/src/hooks/timelineEditingHelpers.ts
+++ b/packages/studio/src/hooks/timelineEditingHelpers.ts
@@ -1,4 +1,5 @@
 import { isHtmlElement } from "@hyperframes/core/runtime/dom-realm";
+import { applyAuthoredTiming } from "@hyperframes/core/studio-preview-mark";
 import { type TimelineElement, usePlayerStore } from "../player/store/playerStore";
 import { toAuthoredStart } from "../player/store/timelineElement";
 import {
@@ -180,7 +181,7 @@ export function patchIframeDomTiming(
   try {
     const el = findTimelineElementInIframe(iframe, element, activeCompositionPath);
     if (!el) return;
-    for (const [name, value] of attrs) el.setAttribute(name, value);
+    applyAuthoredTiming(el, attrs);
   } catch {
     // Cross-origin or mid-navigation — file save is enqueued; iframe patch is best-effort.
   }
diff --git a/packages/studio/src/utils/authoredSource.test.ts b/packages/studio/src/utils/authoredSource.test.ts
index e4e6d26a52..ba2ac6445b 100644
--- a/packages/studio/src/utils/authoredSource.test.ts
+++ b/packages/studio/src/utils/authoredSource.test.ts
@@ -2,6 +2,7 @@
 import { describe, expect, it } from "vitest";
 import {
   PREVIEW_RASTER_ATTR,
+  RUNTIME_STAMPED_ATTR,
   STUDIO_PREVIEW_LAZY_ATTR,
 } from "@hyperframes/core/studio-preview-mark";
 import { liveMarkupWithoutPreviewMarks } from "./authoredSource";
@@ -22,4 +23,13 @@ describe("liveMarkupWithoutPreviewMarks", () => {
     live.innerHTML = `<img src="a.png" loading="lazy" ${STUDIO_PREVIEW_LAZY_ATTR}>`;
     expect(liveMarkupWithoutPreviewMarks(live)).toBe('<div><img src="a.png"></div>');
   });
+
+  it("drops the runtime's stamp so copied markup cannot carry it into a project file", () => {
+    const live = document.createElement("div");
+    live.innerHTML = `<div id="title" data-start="0" data-duration="10" ${RUNTIME_STAMPED_ATTR}="1"></div>`;
+    live.setAttribute(RUNTIME_STAMPED_ATTR, "1");
+    expect(liveMarkupWithoutPreviewMarks(live)).toBe(
+      '<div><div id="title" data-start="0" data-duration="10"></div></div>',
+    );
+  });
 });