fix: step the reading plates aside at click time on long navigator jumps

src/journey/navigation-controller.ts

@@ -94,6 +94,35 @@ export function validateSectionAnchor(
   return heading === null ? null : { id, target };
 }
 
+/** How long a pre-armed interlude waits for the scene loop to take over. */
+const PRE_ARM_TIMEOUT_MS = 1400;
+/** Matches INTERLUDE_RISE_MS in the environment loop. */
+const PRE_ARM_RISE_MS = 1100;
+
+/**
+ * A long navigator scroll passes the chapters in between. While the scene runs
+ * (the loop has set data-gantry), the reading plates step aside at click time
+ * instead of when the sign starts its approach, so those chapters do not flash
+ * past. The loop takes the attribute over as soon as the sign's interlude
+ * starts; if no interlude follows, the plates rise again after a timeout.
+ */
+const preArmInterlude = (): void => {
+  const root = document.documentElement;
+  if (root.dataset.gantry === undefined || root.dataset.interlude === "on") return;
+  root.dataset.interlude = "on";
+  root.dataset.interludeArmed = "nav";
+  window.setTimeout(() => {
+    if (root.dataset.interludeArmed !== "nav") return;
+    root.dataset.interlude = "rise";
+    root.dataset.interludeArmed = "rise";
+    window.setTimeout(() => {
+      if (root.dataset.interludeArmed !== "rise") return;
+      delete root.dataset.interlude;
+      delete root.dataset.interludeArmed;
+    }, PRE_ARM_RISE_MS);
+  }, PRE_ARM_TIMEOUT_MS);
+};
+
 const browserRuntime = (): NavigationRuntime => ({
   getHash: () => window.location.hash,
   pushHash: (hash) => window.history.pushState(window.history.state, "", hash),
@@ -107,10 +136,10 @@ const browserRuntime = (): NavigationRuntime => ({
       return;
     }
     const margin = parseFloat(getComputedStyle(target).scrollMarginTop) || 0;
-    window.scrollTo({
-      top: window.scrollY + target.getBoundingClientRect().top - margin,
-      behavior,
-    });
+    const delta = target.getBoundingClientRect().top - margin;
+    if (behavior === "smooth" && Math.abs(delta) > window.innerHeight * 0.6)
+      preArmInterlude();
+    window.scrollTo({ top: window.scrollY + delta, behavior });
   },
   focusHeading: (target) => {
     // The live reading stage can start or stop while a long journey is still

src/scene/world/environment.ts

@@ -590,6 +590,8 @@ export async function createProceduralSceneGeneration(
         interludeOn = interlude;
         riseUntil = interlude ? 0 : now + INTERLUDE_RISE_MS;
         document.documentElement.dataset.interlude = interlude ? 'on' : 'rise';
+        // A navigator click may have pre-armed the interlude; the loop owns it now.
+        delete document.documentElement.dataset.interludeArmed;
       } else if (riseUntil > 0 && now > riseUntil) {
         riseUntil = 0;
         delete document.documentElement.dataset.interlude;
@@ -630,6 +632,7 @@ export async function createProceduralSceneGeneration(
       disposed = true;
       delete document.documentElement.dataset.gantry;
       delete document.documentElement.dataset.interlude;
+      delete document.documentElement.dataset.interludeArmed;
       // Quality changes reuse the canvas context. Leave texture upload flags at
       // defaults before the next renderer creates its empty array textures.
       const gl = renderer.getContext();