Merge nucleic/brisk-ember-yak-i6ou into main

Mirrored from corpo 49fe7e9.

src/pages/index.astro

@@ -1249,6 +1249,59 @@ const canonical = new URL('/', Astro.site);
 
     activateTechnology(0);
 
+    /* The fixed shell deliberately keeps the masthead and footer outside main's
+       scrollport. Forward gestures that begin there (or in the shell gutter) into
+       main, so the story responds everywhere instead of only between the rules. */
+    if (scrollRoot) {
+      const scrollMainBy = (event: WheelEvent) => {
+        const multiplier = event.deltaMode === WheelEvent.DOM_DELTA_LINE
+          ? 16
+          : event.deltaMode === WheelEvent.DOM_DELTA_PAGE
+            ? scrollRoot.clientHeight
+            : 1;
+        scrollRoot.scrollBy({ top: event.deltaY * multiplier, behavior: 'auto' });
+      };
+
+      document.addEventListener(
+        'wheel',
+        (event) => {
+          if (scrollRoot.contains(event.target as Node) || event.deltaY === 0) return;
+
+          event.preventDefault();
+          scrollMainBy(event);
+        },
+        { capture: true, passive: false },
+      );
+
+      let touchY: number | null = null;
+
+      document.addEventListener(
+        'touchstart',
+        (event) => {
+          touchY = scrollRoot.contains(event.target as Node)
+            ? null
+            : event.touches[0]?.clientY ?? null;
+        },
+        { capture: true, passive: true },
+      );
+
+      document.addEventListener(
+        'touchmove',
+        (event) => {
+          const nextTouchY = event.touches[0]?.clientY;
+          if (touchY === null || nextTouchY === undefined) return;
+
+          event.preventDefault();
+          scrollRoot.scrollBy({ top: touchY - nextTouchY, behavior: 'auto' });
+          touchY = nextTouchY;
+        },
+        { capture: true, passive: false },
+      );
+
+      document.addEventListener('touchend', () => { touchY = null; }, { capture: true, passive: true });
+      document.addEventListener('touchcancel', () => { touchY = null; }, { capture: true, passive: true });
+    }
+
     const stepObserver = new IntersectionObserver(
       (entries) => {
         entries.forEach((entry) => {
@@ -1257,7 +1310,9 @@ const canonical = new URL('/', Astro.site);
           if (Number.isInteger(index)) activateTechnology(index);
         });
       },
-      { root: scrollRoot, rootMargin: '-45% 0px -45% 0px' },
+      /* A wider center band advances the next card earlier, reducing the scroll
+         distance between beats without changing the sticky composition. */
+      { root: scrollRoot, rootMargin: '-38% 0px -38% 0px' },
     );
 
     steps.forEach((step) => stepObserver.observe(step));