diff --git a/api/gateway_chat.py b/api/gateway_chat.py
index f7b48536..2ad544c2 100644
--- a/api/gateway_chat.py
+++ b/api/gateway_chat.py
@@ -508,7 +508,8 @@ def _run_gateway_chat_streaming(
             s.model = model
             s.model_provider = model_provider
             s.save()
-        gateway_session_payload = s.compact() | {"messages": s.messages, "tool_calls": []}
+        from api.streaming import _session_payload_with_full_messages
+        gateway_session_payload = _session_payload_with_full_messages(s, tool_calls=[])
         put_gateway_event("done", {"session": redact_session_data(gateway_session_payload), "usage": usage})
         put_gateway_event("stream_end", {"session_id": session_id})
     except urllib.error.HTTPError as exc:
diff --git a/tests/test_streaming_done_payload_message_count.py b/tests/test_streaming_done_payload_message_count.py
index 1a136bc3..f3c8ded4 100644
--- a/tests/test_streaming_done_payload_message_count.py
+++ b/tests/test_streaming_done_payload_message_count.py
@@ -51,3 +51,16 @@ def test_apperror_payload_uses_full_message_count_helper():
 
     assert "_session_payload_with_full_messages(s, tool_calls=s.tool_calls)" in block
     assert "s.compact() | {'messages': s.messages" not in block
+
+
+def test_gateway_done_payload_uses_full_message_count_helper():
+    """The gateway-routed chat `done` SSE shares the settled-payload path and
+    must also report a message_count matching the embedded transcript (sibling
+    of the two streaming.py sites)."""
+    gateway_source = Path("api/gateway_chat.py").read_text(encoding="utf-8")
+    done_idx = gateway_source.index('put_gateway_event("done"')
+    block_start = gateway_source.rfind("gateway_session_payload =", 0, done_idx)
+    block = gateway_source[block_start:done_idx]
+
+    assert "_session_payload_with_full_messages(s, tool_calls=[])" in block
+    assert 's.compact() | {"messages": s.messages' not in block