diff --git a/src/langbot/pkg/agent/runner/persistent_state_store.py b/src/langbot/pkg/agent/runner/persistent_state_store.py
index 4665f127a..14c9a3403 100644
--- a/src/langbot/pkg/agent/runner/persistent_state_store.py
+++ b/src/langbot/pkg/agent/runner/persistent_state_store.py
@@ -188,7 +188,7 @@ class PersistentStateStore:
                         except json.JSONDecodeError:
                             pass  # Skip invalid JSON
 
-        # Seed external.conversation_id from event.conversation_id if not set
+        # Seed the host conversation ID only before the conversation is reset.
         if self._check_scope_enabled('conversation', binding) and event.conversation_id:
             if 'external.conversation_id' not in snapshot['conversation']:
                 from .context_reset import get_reset_generation
@@ -196,7 +196,8 @@ class PersistentStateStore:
                 generation = await get_reset_generation(
                     self._db_engine, event.workspace_id, event.bot_id, event.conversation_id
                 )
-                snapshot['conversation']['external.conversation_id'] = generation or event.conversation_id
+                if generation is None:
+                    snapshot['conversation']['external.conversation_id'] = event.conversation_id
 
         return snapshot
 
diff --git a/tests/unit_tests/api/service/test_session_context_reset.py b/tests/unit_tests/api/service/test_session_context_reset.py
index 70989432f..6a5892a11 100644
--- a/tests/unit_tests/api/service/test_session_context_reset.py
+++ b/tests/unit_tests/api/service/test_session_context_reset.py
@@ -153,7 +153,7 @@ async def test_reset_starts_new_external_runner_conversation(context_service):
     snapshot = await store.build_snapshot_from_event(event, binding, descriptor)
     generation = await get_reset_generation(engine, 'w', 'b', 'person_u')
     assert isinstance(generation, str) and generation and generation not in {'remote-old', 'person_u'}
-    assert snapshot['conversation']['external.conversation_id'] == generation
+    assert 'external.conversation_id' not in snapshot['conversation']
 
 
 @pytest.mark.asyncio