fix(graph): stop keeping every run's full state in the graph

- a graph reused across a backtest grid held each run's complete state for its whole life
- the state log is written from the run's own state; the ticker attribute it read is removed

tests/test_cli_display.py

@@ -35,21 +35,12 @@ def test_the_other_shapes_are_unchanged(value, expected):
     assert extract_content_string(value) == expected
 
 
-@pytest.mark.unit
-def test_the_state_log_keeps_non_ascii_readable(tmp_path):
-    """Reports can be in any language; the log is read by a person."""
-    from tradingagents.graph.trading_graph import TradingAgentsGraph
-
-    graph = object.__new__(TradingAgentsGraph)
-    graph.config = {"results_dir": str(tmp_path)}
-    graph.ticker = "600519.SS"
-    graph.log_states_dict = {}
-
-    graph._log_state("2026-09-01", {
-        "company_of_interest": "600519.SS", "trade_date": "2026-09-01",
+def _state(ticker, final="评级: 买入"):
+    return {
+        "company_of_interest": ticker, "trade_date": "2026-09-01",
         "market_report": "市场", "sentiment_report": "情绪", "news_report": "新闻",
         "fundamentals_report": "基本面", "investment_plan": "计划",
-        "trader_investment_plan": "交易计划", "final_trade_decision": "评级: 买入",
+        "trader_investment_plan": "交易计划", "final_trade_decision": final,
         "investment_debate_state": {"bull_history": "", "bear_history": "", "history": "",
                                     "current_response": "", "judge_decision": "", "count": 0},
         "risk_debate_state": {"aggressive_history": "", "conservative_history": "",
@@ -57,7 +48,21 @@ def test_the_state_log_keeps_non_ascii_readable(tmp_path):
                               "latest_speaker": "", "current_aggressive_response": "",
                               "current_conservative_response": "", "current_neutral_response": "",
                               "count": 0},
-    })
+    }
+
+
+def _bare_graph(tmp_path):
+    from tradingagents.graph.trading_graph import TradingAgentsGraph
+
+    graph = object.__new__(TradingAgentsGraph)
+    graph.config = {"results_dir": str(tmp_path)}
+    return graph
+
+
+@pytest.mark.unit
+def test_the_state_log_keeps_non_ascii_readable(tmp_path):
+    """Reports can be in any language; the log is read by a person."""
+    _bare_graph(tmp_path)._log_state("2026-09-01", _state("600519.SS"))
 
     written = next(tmp_path.rglob("full_states_log*.json")).read_text(encoding="utf-8")
     assert "买入" in written