fix: 资料流提早显现内容,避免空白缺口被误认为到底

Reveal 加 300px 前置 viewport margin,内容在进入视口前淡入;
无限滚动预加载触发线 200px → 1000px,下一页提前请求。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/components/messageStream/MessageStream.tsx

@@ -62,7 +62,9 @@ export function MessageStream({ scope }: MessageStreamProps) {
           }
         }
       },
-      { rootMargin: "200px" },
+      // Prefetch the next page well before the sentinel is visible so content
+      // is already in place as the user scrolls — no blank gap at the bottom.
+      { rootMargin: "1000px" },
     );
     io.observe(el);
     return () => io.disconnect();

src/motion/Reveal.tsx

@@ -11,6 +11,13 @@ type RevealProps = {
   once?: boolean;
   /** Fraction of the element that must be visible to trigger (0-1). */
   amount?: number;
+  /**
+   * Root margin for the in-view trigger (same semantics as IntersectionObserver
+   * `rootMargin`). The default positive bottom value reveals each block ~300px
+   * *before* it scrolls into view, so long feeds never show a blank gap that
+   * reads as "the bottom" before content fades in.
+   */
+  margin?: string;
 };
 
 /**
@@ -24,6 +31,7 @@ export function Reveal({
   className,
   once = true,
   amount = 0.15,
+  margin = "0px 0px 300px 0px",
 }: RevealProps) {
   return (
     <m.div
@@ -32,7 +40,7 @@ export function Reveal({
       custom={delay}
       initial="hidden"
       whileInView="visible"
-      viewport={{ once, amount }}
+      viewport={{ once, amount, margin }}
     >
       {children}
     </m.div>