diff --git a/src/langbot/pkg/pipeline/aggregator.py b/src/langbot/pkg/pipeline/aggregator.py
index 1af85a65..96358e32 100644
--- a/src/langbot/pkg/pipeline/aggregator.py
+++ b/src/langbot/pkg/pipeline/aggregator.py
@@ -275,6 +275,7 @@ class MessageAggregator:
             message_chain=merged_chain,
             adapter=base_msg.adapter,
             pipeline_uuid=base_msg.pipeline_uuid,
+            routed_by_rule=any(msg.routed_by_rule for msg in messages),
         )
 
     async def flush_all(self) -> None:
diff --git a/tests/unit_tests/pipeline/test_aggregator.py b/tests/unit_tests/pipeline/test_aggregator.py
new file mode 100644
index 00000000..3f14bb9d
--- /dev/null
+++ b/tests/unit_tests/pipeline/test_aggregator.py
@@ -0,0 +1,42 @@
+"""
+MessageAggregator unit tests.
+"""
+
+from importlib import import_module
+
+import langbot_plugin.api.entities.builtin.platform.message as platform_message
+import langbot_plugin.api.entities.builtin.provider.session as provider_session
+
+
+def test_merge_messages_preserves_routed_by_rule_if_any_input_matches(sample_message_event, mock_adapter):
+    """Merged PendingMessage should keep routed_by_rule when any input was rule-routed."""
+    aggregator = import_module('langbot.pkg.pipeline.aggregator')
+    message_aggregator = aggregator.MessageAggregator(ap=None)
+
+    first_message = aggregator.PendingMessage(
+        bot_uuid='test-bot-uuid',
+        launcher_type=provider_session.LauncherTypes.PERSON,
+        launcher_id=12345,
+        sender_id=12345,
+        message_event=sample_message_event,
+        message_chain=platform_message.MessageChain([platform_message.Plain(text='first')]),
+        adapter=mock_adapter,
+        pipeline_uuid='test-pipeline-uuid',
+        routed_by_rule=False,
+    )
+    second_message = aggregator.PendingMessage(
+        bot_uuid='test-bot-uuid',
+        launcher_type=provider_session.LauncherTypes.PERSON,
+        launcher_id=12345,
+        sender_id=12345,
+        message_event=sample_message_event,
+        message_chain=platform_message.MessageChain([platform_message.Plain(text='second')]),
+        adapter=mock_adapter,
+        pipeline_uuid='test-pipeline-uuid',
+        routed_by_rule=True,
+    )
+
+    merged_message = message_aggregator._merge_messages([first_message, second_message])
+
+    assert merged_message.routed_by_rule is True
+    assert str(merged_message.message_chain) == 'first\nsecond'