fix: snap scroll to dialogue typing

src/choreography.js

@@ -220,6 +220,97 @@ export function initRail(lenis) {
   return { jump, setActive };
 }
 
+/* 滚动守卫：避免停在两轮之间只剩背景的中间态 */
+export function initRoundAutoFocus(lenis) {
+  const targets = rounds
+    .filter((round) => round.question && !round.flow)
+    .map((round) => ({ round, section: document.getElementById(`r-${round.id}`) }))
+    .filter((target) => target.section);
+
+  if (!targets.length) return () => {};
+
+  let lockUntil = 0;
+  let currentTarget = "";
+
+  const readY = () => (typeof lenis?.scroll === "number" ? lenis.scroll : window.scrollY);
+
+  const pinDistance = (round) => {
+    const match = String(round.pinLength || "").match(/^\+=([\d.]+)%$/);
+    const ratio = match ? Number(match[1]) / 100 : 1.6;
+    return ratio * (window.innerHeight || document.documentElement.clientHeight);
+  };
+
+  const typingOffset = (round) => {
+    const endProgress = Math.min(round.qEnd + 0.025, round.thinkEnd - 0.03);
+    return Math.max(112, Math.round(pinDistance(round) * endProgress));
+  };
+
+  const focusRound = ({ round, section }, sectionStartY = null) => {
+    const now = performance.now();
+    lockUntil = now + 1150;
+    currentTarget = section.id;
+    const baseY = sectionStartY ?? section.getBoundingClientRect().top + readY();
+    const targetY = baseY + typingOffset(round);
+
+    if (lenis) {
+      lenis.scrollTo(targetY, {
+        duration: 0.85,
+        easing: (t) => 1 - Math.pow(1 - t, 3),
+      });
+    } else {
+      window.scrollTo({ top: targetY, behavior: "smooth" });
+    }
+  };
+
+  const canFocus = ({ section }) => {
+    const now = performance.now();
+    if (now < lockUntil) return false;
+    const rect = section.getBoundingClientRect();
+    if (section.id === currentTarget && rect.top > -12 && rect.top < 12) return false;
+    return rect.top > 24;
+  };
+
+  const findHalfEnteredRound = () => {
+    const vh = window.innerHeight || document.documentElement.clientHeight;
+    const minTop = Math.max(36, vh * 0.08);
+    const maxTop = vh * 0.62;
+
+    return targets.find((target) => {
+      const { section } = target;
+      const rect = section.getBoundingClientRect();
+      if (!canFocus(target)) return false;
+      return rect.top > minTop && rect.top < maxTop && rect.bottom > vh * 0.55;
+    });
+  };
+
+  const checkCurrent = () => {
+    const target = findHalfEnteredRound();
+    if (target) focusRound(target);
+  };
+
+  const triggers = targets.map((section) =>
+    ScrollTrigger.create({
+      trigger: section.section,
+      start: "top 62%",
+      end: "top 8%",
+      onEnter: (self) => {
+        if (canFocus(section)) {
+          const vh = window.innerHeight || document.documentElement.clientHeight;
+          focusRound(section, self.start + vh * 0.62);
+        }
+      },
+    }),
+  );
+
+  window.addEventListener("resize", checkCurrent);
+  window.setTimeout(checkCurrent, 250);
+
+  return () => {
+    triggers.forEach((trigger) => trigger.kill());
+    window.removeEventListener("resize", checkCurrent);
+  };
+}
+
 /* 降级：reduced motion 直接展示全部内容 */
 export function applyReducedMotion() {
   rounds

src/main.js

@@ -5,6 +5,7 @@ import {
   applyReducedMotion,
   initChoreography,
   initRail,
+  initRoundAutoFocus,
   initSmoothScroll,
   playBoot,
 } from "./choreography";
@@ -28,6 +29,7 @@ renderRail(document.getElementById("session-rail"), rail.jump);
 
 if (!reduced) {
   initChoreography(mind, rail.setActive);
+  initRoundAutoFocus(lenis);
   playBoot(mind);
 } else {
   applyReducedMotion();