[core] Bound event pagination against non-progressing pages

.changeset/spotty-pagination-progress.md

@@ -0,0 +1,5 @@
+---
+'@workflow/core': patch
+---
+
+Further harden event pagination code, failing cleanly when a page reports more results but adds no new events and would get stuck in a loop

packages/core/src/runtime/helpers.test.ts

@@ -283,4 +283,60 @@ describe('loadWorkflowRunEvents', () => {
     });
     expect(eventsListMock).toHaveBeenCalledTimes(1);
   });
+
+  it('fails when a page advances the cursor but adds no new events', async () => {
+    // A backend that keeps returning fresh cursors with empty pages would
+    // never repeat a cursor, so the cursor-based guards never trip. Zero
+    // forward progress must still bound the loop on the first such page.
+    eventsListMock.mockResolvedValue({
+      data: [],
+      cursor: 'eid:evnt_a',
+      hasMore: true,
+    });
+
+    await expect(loadWorkflowRunEvents('wrun_test')).rejects.toMatchObject({
+      code: 'WORLD_CONTRACT_ERROR',
+    });
+    expect(eventsListMock).toHaveBeenCalledTimes(1);
+  });
+
+  it('fails when a non-final page is entirely overlapping events', async () => {
+    // Real events on page 1, then a page that re-serves only already-seen
+    // events while still claiming `hasMore` with a brand-new cursor.
+    eventsListMock.mockResolvedValueOnce({
+      data: [makeEvent('evnt_a'), makeEvent('evnt_b')],
+      cursor: 'eid:evnt_b',
+      hasMore: true,
+    });
+    eventsListMock.mockResolvedValueOnce({
+      data: [makeEvent('evnt_a'), makeEvent('evnt_b')],
+      cursor: 'eid:evnt_b_again',
+      hasMore: true,
+    });
+
+    await expect(loadWorkflowRunEvents('wrun_test')).rejects.toMatchObject({
+      code: 'WORLD_CONTRACT_ERROR',
+    });
+    expect(eventsListMock).toHaveBeenCalledTimes(2);
+  });
+
+  it('still completes when a trailing empty page closes pagination', async () => {
+    // Regression guard: an empty final page is legitimate as long as it does
+    // not claim `hasMore`, and must not be mistaken for non-progression.
+    eventsListMock.mockResolvedValueOnce({
+      data: [makeEvent('evnt_a')],
+      cursor: 'eid:evnt_a',
+      hasMore: true,
+    });
+    eventsListMock.mockResolvedValueOnce({
+      data: [],
+      cursor: null,
+      hasMore: false,
+    });
+
+    const result = await loadWorkflowRunEvents('wrun_test');
+
+    expect(result.events.map((event) => event.eventId)).toEqual(['evnt_a']);
+    expect(eventsListMock).toHaveBeenCalledTimes(2);
+  });
 });

packages/core/src/runtime/helpers.ts

@@ -348,7 +348,8 @@ function assertEventPaginationProgress(
   runId: string,
   hasMore: boolean,
   cursor: string | null,
-  requestedCursors: Set<string>
+  requestedCursors: Set<string>,
+  addedNewEvents: boolean
 ): void {
   if (!hasMore) {
     return;
@@ -362,6 +363,19 @@ function assertEventPaginationProgress(
   if (requestedCursors.has(cursor)) {
     throw eventPaginationContractError(runId, 'repeated a cursor');
   }
+  // A non-final page over an ascending cursor must surface at least one event
+  // we have not already seen. The existing guards above only catch a cursor
+  // that repeats a value we requested before; a backend that keeps handing
+  // back fresh cursors with empty or fully-overlapping pages would otherwise
+  // spin `while (hasMore)` forever while `appendUniqueEvents` keeps the result
+  // flat. Treating zero forward progress as a contract violation bounds the
+  // loop without an arbitrary page cap.
+  if (!addedNewEvents) {
+    throw eventPaginationContractError(
+      runId,
+      'reported more pages without making progress'
+    );
+  }
 }
 
 function shouldRetryWithoutEventCursor(
@@ -449,13 +463,15 @@ export async function loadWorkflowRunEvents(
           throw error;
         }
 
+        const eventsBeforeAppend = loadedEvents.length;
         appendUniqueEvents(loadedEvents, loadedEventIds, response.data);
         hasMore = response.hasMore;
         assertEventPaginationProgress(
           runId,
           hasMore,
           response.cursor,
-          requestedCursors
+          requestedCursors,
+          loadedEvents.length > eventsBeforeAppend
         );
         // Preserve the last non-null cursor across pages. A World may
         // legitimately return `{ data: [], cursor: null, hasMore: false }`