Fix

Author: alwx

packages/core/src/js/tracing/timeToDisplayCoordinator.ts

@@ -105,8 +105,10 @@ function notifyListeners(entry: SpanRegistry): void {
 }
 
 function performCleanup(kind: DisplayKind, parentSpanId: string, entry: SpanRegistry): void {
-  const liveCheckpoints = entry.checkpoints.size - entry.sticky.size;
-  if (liveCheckpoints === 0 && entry.listeners.size === 0) {
+  if (entry.sticky.size > 0) {
+    return;
+  }
+  if (entry.checkpoints.size === 0 && entry.listeners.size === 0) {
     cancelPendingUpFlip(entry);
     registries[kind].delete(parentSpanId);
   }

packages/core/test/tracing/timeToDisplayCoordinator.test.ts

@@ -127,4 +127,16 @@ describe('timeToDisplayCoordinator', () => {
     registerCheckpoint('ttfd', SPAN_FIRST, 'b', false);
     expect(isAllReady('ttfd', SPAN_FIRST)).toBe(false);
   });
+
+  test('sticky-blocker survives sibling unmounts and continues to block new peers', () => {
+    const unregisterA = registerCheckpoint('ttfd', SPAN_FIRST, 'a', false);
+    const unregisterB = registerCheckpoint('ttfd', SPAN_FIRST, 'b', true);
+
+    unregisterA(); // A becomes sticky
+    unregisterB();
+
+    registerCheckpoint('ttfd', SPAN_FIRST, 'c', true);
+    flushDefer();
+    expect(isAllReady('ttfd', SPAN_FIRST)).toBe(false);
+  });
 });