diff --git a/src/node/wrapper_helpers.py b/src/node/wrapper_helpers.py
index fe631e21f..8710ed556 100644
--- a/src/node/wrapper_helpers.py
+++ b/src/node/wrapper_helpers.py
@@ -12,6 +12,13 @@ EVENT_PROPAGATED = "message_propagated"
 EVENT_SENT = "message_sent"
 EVENT_ERROR = "message_error"
 
+# MaxTimeInCache from send_service.nim.
+MAX_TIME_IN_CACHE_S = 60.0
+# Extra slack to cover the background retry loop tick after the window expires.
+CACHE_EXPIRY_SLACK_S = 10.0
+ERROR_AFTER_CACHE_EXPIRY_TIMEOUT_S = MAX_TIME_IN_CACHE_S + CACHE_EXPIRY_SLACK_S
+RETRY_WINDOW_EXPIRED_MSG = "Unable to send within retry time window"
+
 
 class EventCollector:
     """Thread-safe collector for async node events.
@@ -84,6 +91,27 @@ def wait_for_error(collector: EventCollector, request_id: str, timeout_s: float)
     return wait_for_event(collector, request_id, is_error_event, timeout_s)
 
 
+def assert_no_error(collector: EventCollector, request_id: str, context: str = "") -> None:
+    """Assert that no message_error event is currently buffered for `request_id`."""
+    event = wait_for_error(collector, request_id, timeout_s=0)
+    suffix = f" ({context})" if context else ""
+    assert event is None, f"Unexpected message_error event{suffix}: {event}"
+
+
+def assert_no_sent(collector: EventCollector, request_id: str, context: str = "") -> None:
+    """Assert that no message_sent event is currently buffered for `request_id`."""
+    event = wait_for_sent(collector, request_id, timeout_s=0)
+    suffix = f" ({context})" if context else ""
+    assert event is None, f"Unexpected message_sent event{suffix}: {event}"
+
+
+def assert_no_propagated(collector: EventCollector, request_id: str, context: str = "") -> None:
+    """Assert that no message_propagated event is currently buffered for `request_id`."""
+    event = wait_for_propagated(collector, request_id, timeout_s=0)
+    suffix = f" ({context})" if context else ""
+    assert event is None, f"Unexpected message_propagated event{suffix}: {event}"
+
+
 def wait_for_connected(
     collector: EventCollector,
     timeout_s: float = 10.0,
@@ -165,3 +193,16 @@ def create_message_bindings(**overrides) -> dict:
     }
     envelope.update(overrides)
     return envelope
+
+
+def assert_no_unknown_request_ids(collector: EventCollector, issued_request_ids) -> None:
+    """Cross-association guard: every event carrying a requestId must belong
+    to one of the request ids we issued. Catches events that get attached to
+    the wrong request id under concurrency.
+    """
+    issued = set(issued_request_ids)
+    for event in collector.events:
+        event_request_id = event.get("requestId")
+        if event_request_id is None:
+            continue
+        assert event_request_id in issued, f"Event carries an unknown requestId={event_request_id!r}, " f"not in issued set {issued}. Event: {event}"
diff --git a/tests/wrappers_tests/test_send_e2e_part1.py b/tests/wrappers_tests/test_send_e2e_part1.py
index 7f6a1d8f2..7ef272f0d 100644
--- a/tests/wrappers_tests/test_send_e2e_part1.py
+++ b/tests/wrappers_tests/test_send_e2e_part1.py
@@ -1,6 +1,4 @@
 from concurrent.futures import ThreadPoolExecutor
-from time import time_ns
-
 import pytest
 from src.env_vars import NODE_2
 from src.steps.common import StepsCommon
@@ -235,6 +233,7 @@ class TestSendBeforeRelay(StepsStore):
               -> SuccessfullyPropagated -> SuccessfullyValidated
 
         """
+        sender_collector = EventCollector()
         store_node = WakuNode(NODE_2, f"s20_store_node_{self.test_id}")
         store_node.start(
             relay="true",
diff --git a/tests/wrappers_tests/test_send_e2e_part2.py b/tests/wrappers_tests/test_send_e2e_part2.py
index 33f66fb98..14add387d 100644
--- a/tests/wrappers_tests/test_send_e2e_part2.py
+++ b/tests/wrappers_tests/test_send_e2e_part2.py
@@ -1,5 +1,4 @@
 import base64
-
 import pytest
 from src.steps.common import StepsCommon
 from src.libs.common import delay, to_base64
@@ -15,7 +14,6 @@ from src.node.wrapper_helpers import (
     wait_for_sent,
     wait_for_error,
 )
-from src.steps.store import StepsStore
 from tests.wrappers_tests.conftest import build_node_config
 
 logger = get_custom_logger(__name__)