fix: drop past-memory directive and placeholder from agent prompts when memory is empty (#572)

tradingagents/agents/managers/portfolio_manager.py

@@ -22,6 +22,17 @@ def create_portfolio_manager(llm, memory):
         for i, rec in enumerate(past_memories, 1):
             past_memory_str += rec["recommendation"] + "\n\n"
 
+        lessons_line = (
+            f"- Lessons from past decisions: **{past_memory_str.strip()}**\n"
+            if past_memories
+            else ""
+        )
+        thesis_instruction = (
+            "3. **Investment Thesis**: Detailed reasoning anchored in the analysts' debate and past reflections."
+            if past_memories
+            else "3. **Investment Thesis**: Detailed reasoning anchored in the analysts' debate."
+        )
+
         prompt = f"""As the Portfolio Manager, synthesize the risk analysts' debate and deliver the final trading decision.
 
 {instrument_context}
@@ -38,12 +49,11 @@ def create_portfolio_manager(llm, memory):
 **Context:**
 - Research Manager's investment plan: **{research_plan}**
 - Trader's transaction proposal: **{trader_plan}**
-- Lessons from past decisions: **{past_memory_str}**
-
+{lessons_line}
 **Required Output Structure:**
 1. **Rating**: State one of Buy / Overweight / Hold / Underweight / Sell.
 2. **Executive Summary**: A concise action plan covering entry strategy, position sizing, key risk levels, and time horizon.
-3. **Investment Thesis**: Detailed reasoning anchored in the analysts' debate and past reflections.
+{thesis_instruction}
 
 ---