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.

tradingagents/agents/schemas.py

@@ -21,7 +21,20 @@ from __future__ import annotations
 from enum import Enum
 from typing import Literal
 
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Field, field_validator
+
+# LLMs sometimes write a placeholder string ("None", "N/A", ...) into an optional
+# numeric field instead of omitting it. Coerce those to None so the structured
+# call validates instead of erroring (#1058). Pydantic still parses real numeric
+# strings ("189.5") to float.
+_NULLISH_FLOAT = {"", "none", "n/a", "na", "null", "nil", "-", "tbd", "unknown"}
+
+
+def _coerce_optional_float(value):
+    if isinstance(value, str) and value.strip().lower() in _NULLISH_FLOAT:
+        return None
+    return value
+
 
 # ---------------------------------------------------------------------------
 # Shared rating types
@@ -136,6 +149,11 @@ class TraderProposal(BaseModel):
         description="Optional sizing guidance, e.g. '5% of portfolio'.",
     )
 
+    @field_validator("entry_price", "stop_loss", mode="before")
+    @classmethod
+    def _nullish_float_to_none(cls, v):
+        return _coerce_optional_float(v)
+
 
 def render_trader_proposal(proposal: TraderProposal) -> str:
     """Render a TraderProposal to markdown.
@@ -204,6 +222,11 @@ class PortfolioDecision(BaseModel):
         description="Optional recommended holding period, e.g. '3-6 months'.",
     )
 
+    @field_validator("price_target", mode="before")
+    @classmethod
+    def _nullish_float_to_none(cls, v):
+        return _coerce_optional_float(v)
+
 
 def render_pm_decision(decision: PortfolioDecision) -> str:
     """Render a PortfolioDecision back to the markdown shape the rest of the system expects.