fix: make the reading viewport a script-driven scroll container so sticky and view timelines work

src/journey/navigation-controller.ts

@@ -99,8 +99,19 @@ const browserRuntime = (): NavigationRuntime => ({
   pushHash: (hash) => window.history.pushState(window.history.state, "", hash),
   replaceHash: (hash) =>
     window.history.replaceState(window.history.state, "", hash),
-  scrollTarget: (target, behavior) =>
-    target.scrollIntoView({ behavior, block: "start" }),
+  scrollTarget: (target, behavior) => {
+    // Inside the live reading stage the document is the only real scroller;
+    // scrollIntoView would move the script-driven inner viewport instead.
+    if (target.closest('[data-reading-stage="live"]') === null) {
+      target.scrollIntoView({ behavior, block: "start" });
+      return;
+    }
+    const margin = parseFloat(getComputedStyle(target).scrollMarginTop) || 0;
+    window.scrollTo({
+      top: window.scrollY + target.getBoundingClientRect().top - margin,
+      behavior,
+    });
+  },
   focusHeading: (target) => {
     target
       .querySelector<HTMLElement>('h1[tabindex="-1"], h2[tabindex="-1"]')

src/scene/world/sign-stage.ts

@@ -48,8 +48,10 @@ export function createSignStage(resources: SceneResourceBag) {
       Math.min(window.scrollY, contentHeight - viewportHeight),
     );
     if (offset !== lastOffset) {
-      main.style.transform = `translate3d(0, ${-offset}px, 0)`;
+      // The viewport is a real (overflow: hidden) scroll container driven by
+      // the document scroll, so sticky and view-timeline layout work inside it.
       lastOffset = offset;
+      viewport.scrollTop = offset;
     }
     // Quantize the opening reveal: the mask image is rebuilt at most
     // REVEAL_STEPS times on the way in instead of on every scroll event.
@@ -149,6 +151,21 @@ export function createSignStage(resources: SceneResourceBag) {
   };
 
   resources.listen(window, 'scroll', moveContent, { passive: true });
+  // Anything the browser scrolls inside the viewport (find-in-page, focus,
+  // scrollIntoView) is forwarded to the document, which stays the one scroller.
+  if (viewport)
+    resources.listen(
+      viewport,
+      'scroll',
+      () => {
+        if (!ownsStage() || Number.isNaN(lastOffset)) return;
+        const drift = viewport.scrollTop - lastOffset;
+        if (Math.abs(drift) < 1) return;
+        viewport.scrollTop = lastOffset;
+        window.scrollBy({ top: drift, behavior: 'instant' });
+      },
+      { passive: true },
+    );
   const layoutChanged = () => {
     dirty = true;
     if (ownsStage()) update(root.clientWidth, window.innerHeight);
@@ -184,7 +201,7 @@ export function createSignStage(resources: SceneResourceBag) {
         delete stage.dataset.readingStage;
         stage.style.removeProperty('height');
       }
-      main.style.removeProperty('transform');
+      if (viewport) viewport.scrollTop = 0;
       viewport?.style.removeProperty('mask-image');
       viewport?.style.removeProperty('height');
       for (const image of lazyImages) image.loading = 'lazy';

src/styles/world.css

@@ -524,12 +524,12 @@
 .reading-stage[data-reading-stage='live'] > .reading-viewport {
   position: sticky;
   top: 0;
-  overflow: clip;
+  /* A real scroll container (scrolled from script, never by the user), so
+     sticky children and view timelines resolve against the reading window. */
+  overflow: hidden;
+  overscroll-behavior: none;
   isolation: isolate;
 }
-.reading-stage[data-reading-stage='live'] .portfolio-main {
-  will-change: transform;
-}
 
 /* The stationary reading edge supplies the live reveal. View timelines use
    layout positions, which no longer follow the translated content here. */