fix(schema): coerce null-ish strings in optional float fields

A weak model can write a placeholder ('None', 'N/A') into an optional price
field, tripping schema validation. Coerce null-ish strings to None on the
trader/PM float fields; real numeric strings still parse.

tests/test_structured_agents.py

@@ -15,6 +15,7 @@ from pydantic import ValidationError
 from tradingagents.agents.analysts.sentiment_analyst import create_sentiment_analyst
 from tradingagents.agents.managers.research_manager import create_research_manager
 from tradingagents.agents.schemas import (
+    PortfolioDecision,
     PortfolioRating,
     ResearchPlan,
     SentimentBand,
@@ -67,6 +68,36 @@ class TestRenderTraderProposal:
         assert "FINAL TRANSACTION PROPOSAL: **SELL**" in md
 
 
+@pytest.mark.unit
+class TestNullishFloatCoercion:
+    """A weak LLM may write "None"/"N/A" into an optional float field (#1058);
+    coerce those to None so the structured call validates instead of erroring."""
+
+    def test_trader_nullish_strings_coerce_to_none(self):
+        for sentinel in ("None", "N/A", "null", "-", "", "TBD"):
+            p = TraderProposal(
+                action=TraderAction.HOLD,
+                reasoning="x",
+                entry_price=sentinel,
+                stop_loss=sentinel,
+            )
+            assert p.entry_price is None
+            assert p.stop_loss is None
+
+    def test_trader_real_numeric_string_still_parses(self):
+        p = TraderProposal(action=TraderAction.BUY, reasoning="x", entry_price="189.5")
+        assert p.entry_price == 189.5
+
+    def test_pm_nullish_price_target_coerces_to_none(self):
+        d = PortfolioDecision(
+            rating=PortfolioRating.OVERWEIGHT,
+            executive_summary="s",
+            investment_thesis="t",
+            price_target="N/A",
+        )
+        assert d.price_target is None
+
+
 @pytest.mark.unit
 class TestRenderResearchPlan:
     def test_required_fields(self):