feat: integrate Pi backend and Pi Web

pi-web/lib/chat-lazy-load.ts

@@ -0,0 +1,22 @@
+export const VISIBLE_PAGE_SIZE = 50;
+
+export function getVisibleRenderWindow(totalCount: number, visibleCount: number): {
+  startIndex: number;
+  hasMore: boolean;
+} {
+  const clampedVisibleCount = Math.min(Math.max(visibleCount, 0), Math.max(totalCount, 0));
+  const startIndex = Math.max(0, totalCount - clampedVisibleCount);
+  return { startIndex, hasMore: startIndex > 0 };
+}
+
+export function getNextVisibleCount(currentVisibleCount: number, pageSize = VISIBLE_PAGE_SIZE): number {
+  return currentVisibleCount + pageSize;
+}
+
+export function captureScrollDistance(scrollHeight: number, scrollTop: number): number {
+  return scrollHeight - scrollTop;
+}
+
+export function restoreScrollTop(scrollHeight: number, savedDistance: number): number {
+  return Math.max(0, scrollHeight - savedDistance);
+}