fix(test): poll for snapshot before starting Router 2 in indexers_sync (#6707)

Signed-off-by: PeaBrane <yanrpei@gmail.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

tests/router/common.py

@@ -1485,9 +1485,36 @@ def _test_router_indexers_sync(
 
             await asyncio.sleep(5)
 
-        # Wait for a second before creating the second router
-        logger.info("Waiting for 1 second before creating second router")
-        await asyncio.sleep(1)
+        # Wait for snapshot to be available before creating second router.
+        # In JetStream mode, the background task may purge acknowledged messages
+        # from the stream before the snapshot upload completes. Poll the object
+        # store so Router 2 can reliably download the snapshot on startup.
+        if durable_kv_events:
+            component_subject = f"namespace.{engine_workers.namespace}.component.{engine_workers.component_name}"
+            slugified = component_subject.lower().replace(".", "-").replace("_", "-")
+            bucket_name = f"{slugified}-radix-bucket"
+            nc = await nats.connect(servers=_nats_server())
+            try:
+                js = nc.jetstream()
+                for attempt in range(50):
+                    try:
+                        obj_store = await js.object_store(bucket_name)
+                        await obj_store.get("radix-state")
+                        logger.info(
+                            f"Snapshot available in object store (attempt {attempt + 1})"
+                        )
+                        break
+                    except Exception:
+                        await asyncio.sleep(0.1)
+                else:
+                    assert False, (
+                        f"Snapshot not found in bucket '{bucket_name}' after 50 attempts (5s). "
+                        f"Router 1 sent 25 requests with snapshot_threshold=20, snapshot should exist."
+                    )
+            finally:
+                await nc.close()
+        else:
+            await asyncio.sleep(1)
 
         # Create second runtime and endpoint for router 2
         logger.info("Creating second KV router with its own runtime")