feat(config): expose sampling temperature and document reproducibility

Adds a cross-provider temperature config (and TRADINGAGENTS_TEMPERATURE),
forwarded to every LLM client when set, so runs can be made less variable
on models that honor it. Adds a README "Reproducibility" section that
separates the sources of run-to-run variation, what users can control
(temperature, non-reasoning model, pinned date), and what is inherent to
LLM-driven analysis, and notes that the identity and verified-data fixes
already removed the "different companies / fabricated prices" variance.

#178 #168

tests/test_temperature_config.py

@@ -0,0 +1,80 @@
+"""Tests for the configurable sampling temperature (#178/#168).
+
+Temperature is a cross-provider knob: when set it must reach the underlying
+chat client; when unset the provider keeps its own default.
+"""
+
+import importlib
+
+import pytest
+
+from tradingagents.llm_clients.factory import create_llm_client
+
+
+@pytest.mark.unit
+class TestTemperatureForwarding:
+    @pytest.mark.parametrize(
+        "provider,model",
+        [
+            ("openai", "gpt-4.1"),
+            ("anthropic", "claude-sonnet-4-6"),
+            ("google", "gemini-2.5-flash"),
+            ("deepseek", "deepseek-chat"),
+        ],
+    )
+    def test_temperature_reaches_client_when_set(self, provider, model):
+        llm = create_llm_client(
+            provider=provider, model=model, temperature=0.0, api_key="placeholder"
+        ).get_llm()
+        assert llm.temperature == 0.0
+
+    def test_temperature_omitted_leaves_provider_default(self):
+        # Not passing temperature must not force it to a value.
+        llm = create_llm_client(
+            provider="openai", model="gpt-4.1", api_key="placeholder"
+        ).get_llm()
+        # langchain's default is unset/None, not 0.0
+        assert llm.temperature is None
+
+
+@pytest.mark.unit
+class TestTemperatureEnvOverlay:
+    def test_env_sets_temperature(self, monkeypatch):
+        import tradingagents.default_config as dc
+        monkeypatch.setenv("TRADINGAGENTS_TEMPERATURE", "0.2")
+        importlib.reload(dc)
+        # Stored on config (string from env is fine; consumed via float()).
+        assert dc.DEFAULT_CONFIG["temperature"] in ("0.2", 0.2)
+        assert float(dc.DEFAULT_CONFIG["temperature"]) == 0.2
+        monkeypatch.delenv("TRADINGAGENTS_TEMPERATURE", raising=False)
+        importlib.reload(dc)
+
+    def test_default_temperature_is_none(self, monkeypatch):
+        import tradingagents.default_config as dc
+        monkeypatch.delenv("TRADINGAGENTS_TEMPERATURE", raising=False)
+        importlib.reload(dc)
+        assert dc.DEFAULT_CONFIG["temperature"] is None
+
+
+@pytest.mark.unit
+class TestProviderKwargsTemperature:
+    """_get_provider_kwargs float-coerces and forwards temperature, or omits it."""
+
+    def _kwargs_for(self, temperature):
+        from tradingagents.graph.trading_graph import TradingAgentsGraph
+        # Call the method without constructing the full graph.
+        graph = TradingAgentsGraph.__new__(TradingAgentsGraph)
+        graph.config = {"llm_provider": "openai", "temperature": temperature}
+        return TradingAgentsGraph._get_provider_kwargs(graph)
+
+    def test_float_string_coerced(self):
+        assert self._kwargs_for("0.3")["temperature"] == 0.3
+
+    def test_float_passthrough(self):
+        assert self._kwargs_for(0.0)["temperature"] == 0.0
+
+    def test_none_omitted(self):
+        assert "temperature" not in self._kwargs_for(None)
+
+    def test_empty_string_omitted(self):
+        assert "temperature" not in self._kwargs_for("")