fix(agent): scope subagent reply dedupe to origin message

Made-with: Cursor

tests/agent/test_loop_save_turn.py

@@ -727,6 +727,7 @@ def test_set_tool_context_passes_thread_session_key_to_spawn(tmp_path: Path) ->
     loop._set_tool_context(
         "slack",
         "C123",
+        message_id="msg-123",
         metadata={"slack": {"thread_ts": "1700.42", "channel_type": "channel"}},
         session_key="slack:C123:1700.42",
     )
@@ -734,6 +735,7 @@ def test_set_tool_context_passes_thread_session_key_to_spawn(tmp_path: Path) ->
     spawn_tool = loop.tools.get("spawn")
     assert spawn_tool is not None
     assert spawn_tool._session_key.get() == "slack:C123:1700.42"
+    assert spawn_tool._origin_message_id.get() == "msg-123"
 
 
 @pytest.mark.asyncio
@@ -766,14 +768,17 @@ async def test_system_subagent_followup_uses_thread_session_and_slack_metadata(t
             chat_id="slack:C123",
             content="subagent result",
             session_key_override="slack:C123:1700.42",
-            metadata={"subagent_task_id": "sub-1"},
+            metadata={"subagent_task_id": "sub-1", "origin_message_id": "msg-123"},
         )
     )
 
     assert outbound is not None
     assert outbound.channel == "slack"
     assert outbound.chat_id == "C123"
-    assert outbound.metadata == {"slack": {"thread_ts": "1700.42"}}
+    assert outbound.metadata == {
+        "slack": {"thread_ts": "1700.42"},
+        "origin_message_id": "msg-123",
+    }
     assert "thread question" in seen["initial_messages"][1]["content"]
 
     loop.sessions.invalidate("slack:C123:1700.42")