feat(reporting): share the report-tree writer between the CLI and the API

The per-section markdown report tree was written only by the CLI, so programmatic
(TradingAgentsGraph) runs produced no saved reports.

- Extract the writer into tradingagents/reporting.write_report_tree.
- The CLI's save_report_to_disk delegates to it (no behavior change).
- Add TradingAgentsGraph.save_reports(final_state, ticker) so headless/API callers
  get the same report tree, defaulting under results_dir.

tests/test_reporting.py

@@ -0,0 +1,50 @@
+"""Report parity: the shared writer produces the report tree for the CLI and the
+programmatic API alike (#1037)."""
+
+from types import SimpleNamespace
+
+import pytest
+
+from tradingagents.graph.trading_graph import TradingAgentsGraph
+from tradingagents.reporting import write_report_tree
+
+
+def _state():
+    return {
+        "market_report": "MKT",
+        "news_report": "NEWS",
+        "investment_debate_state": {"judge_decision": "RM PLAN"},
+        "trader_investment_plan": "TRADE",
+        "risk_debate_state": {"judge_decision": "PM DECISION"},
+    }
+
+
+@pytest.mark.unit
+def test_write_report_tree_creates_files(tmp_path):
+    out = write_report_tree(_state(), "AAPL", tmp_path)
+    assert out.name == "complete_report.md"
+    assert (tmp_path / "1_analysts" / "market.md").read_text() == "MKT"
+    assert (tmp_path / "1_analysts" / "news.md").read_text() == "NEWS"
+    assert (tmp_path / "2_research" / "manager.md").read_text() == "RM PLAN"
+    assert (tmp_path / "3_trading" / "trader.md").read_text() == "TRADE"
+    assert (tmp_path / "5_portfolio" / "decision.md").read_text() == "PM DECISION"
+    complete = out.read_text()
+    assert "Trading Analysis Report: AAPL" in complete
+    assert "MKT" in complete and "PM DECISION" in complete
+
+
+@pytest.mark.unit
+def test_save_reports_explicit_path(tmp_path):
+    # Unbound: with an explicit save_path, the method doesn't touch self/config.
+    out = TradingAgentsGraph.save_reports(None, _state(), "AAPL", save_path=tmp_path)
+    assert (tmp_path / "complete_report.md").exists()
+    assert out == tmp_path / "complete_report.md"
+
+
+@pytest.mark.unit
+def test_save_reports_defaults_under_results_dir(tmp_path):
+    mock_self = SimpleNamespace(config={"results_dir": str(tmp_path)})
+    out = TradingAgentsGraph.save_reports(mock_self, _state(), "AAPL")
+    assert out.exists()
+    assert out.parent.parent.name == "reports"  # results_dir/reports/AAPL_<stamp>/...
+    assert out.parent.name.startswith("AAPL_")