fix: keep older-blocks pagination in shadow delta view

app/internal-explorer/blocks/page.tsx

@@ -13,6 +13,7 @@ import { ActiveBlockButton } from '../components/ActiveBlockButton';
 import { explorerApi } from '../library/client';
 import { formatInteger } from '../library/explorer-format';
 import { explorerHref } from '../library/links';
+import { nextShadowCursor } from '../library/shadow-pagination';
 import type { BlocksResponse, ShadowBlockSummary } from '../library/types';
 import { useExplorerChain } from '../library/useExplorerChain';
 import { useShadowDelta } from '../library/useShadowDelta';
@@ -76,13 +77,13 @@ function BlocksContent() {
     setShadowCandidates({});
 
     explorerApi
-      .recentShadowBlocks(chain, { limit: PAGE_LIMIT }, controller.signal)
+      .recentShadowBlocks(chain, { limit: PAGE_LIMIT, before: cursor }, controller.signal)
       .then(async (shadows) => {
         if (cancelled) return;
         if (shadows.length === 0) {
           setData({
             blocks: [],
-            page: { cursor: null, limit: PAGE_LIMIT, latestBlockNumber: 0, nextCursor: null, hasMore: false },
+            page: { cursor: cursor ?? null, limit: PAGE_LIMIT, latestBlockNumber: 0, nextCursor: null, hasMore: false },
           });
           return;
         }
@@ -101,15 +102,17 @@ function BlocksContent() {
             .map((shadow) => [shadow.canonicalHash!.toLowerCase(), [shadow]]),
         );
 
+        const nextCursor = nextShadowCursor(shadows, PAGE_LIMIT);
+
         setShadowCandidates(candidates);
         setData({
           blocks: orderedBlocks,
           page: {
-            cursor: null,
+            cursor: cursor ?? null,
             limit: PAGE_LIMIT,
             latestBlockNumber: orderedBlocks[0]?.number ?? 0,
-            nextCursor: null,
-            hasMore: false,
+            nextCursor,
+            hasMore: nextCursor !== null,
           },
         });
       })
@@ -125,7 +128,7 @@ function BlocksContent() {
       cancelled = true;
       controller.abort();
     };
-  }, [chain, showShadowDelta]);
+  }, [chain, cursor, showShadowDelta]);
 
   return (
     <div className="animate-in flex flex-col gap-6">

app/internal-explorer/library/shadow-pagination.test.ts

@@ -0,0 +1,31 @@
+import { describe, expect, it } from 'vitest';
+
+import { nextShadowCursor } from './shadow-pagination';
+
+const PAGE_LIMIT = 25;
+
+function shadowsEndingAt(oldest: number, count: number): { number: number }[] {
+  return Array.from({ length: count }, (_, index) => ({ number: oldest + count - 1 - index }));
+}
+
+describe('nextShadowCursor', () => {
+  it('returns the oldest block number when a full page is returned', () => {
+    const shadows = shadowsEndingAt(100, PAGE_LIMIT);
+    expect(shadows.at(-1)?.number).toBe(100);
+    expect(nextShadowCursor(shadows, PAGE_LIMIT)).toBe(100);
+  });
+
+  it('returns null on a short page (source exhausted)', () => {
+    const shadows = shadowsEndingAt(100, PAGE_LIMIT - 1);
+    expect(nextShadowCursor(shadows, PAGE_LIMIT)).toBeNull();
+  });
+
+  it('returns null when the oldest block is genesis (0)', () => {
+    const shadows = shadowsEndingAt(0, PAGE_LIMIT);
+    expect(nextShadowCursor(shadows, PAGE_LIMIT)).toBeNull();
+  });
+
+  it('returns null for an empty page', () => {
+    expect(nextShadowCursor([], PAGE_LIMIT)).toBeNull();
+  });
+});

app/internal-explorer/library/shadow-pagination.ts

@@ -0,0 +1,14 @@
+// Pagination cursor for the shadow-delta block view. Shadow blocks come back
+// newest-first; the API's `before` param is an *exclusive* block-number cutoff,
+// so the next page starts at the oldest block returned (no overlap, no gap). A
+// short page means the source is exhausted.
+import type { ShadowBlockSummary } from './types';
+
+export function nextShadowCursor(
+  shadows: Pick<ShadowBlockSummary, 'number'>[],
+  pageLimit: number,
+): number | null {
+  if (shadows.length < pageLimit) return null;
+  const oldest = shadows.at(-1)?.number;
+  return oldest === undefined || oldest <= 0 ? null : oldest;
+}