fix: Add missing increment_state method and improve chat history persistence

- Add increment_state method (lines 356-359) for numeric state management
- Fix empty chat history save condition to track agent existence properly
- Improve robustness by checking agent is not None before accessing chat_history
- Enhance memory persistence by saving even empty chat histories to track agent state

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Mervin Praison <MervinPraison@users.noreply.github.com>
Co-Authored-By: Claude <noreply@anthropic.com>

Author: 3 people

src/praisonai-agents/praisonaiagents/session.py

@@ -325,11 +325,11 @@ def _save_agent_chat_histories(self) -> None:
 
         for agent_key, agent_data in self._agents.items():
             agent = agent_data["agent"]
-            if hasattr(agent, 'chat_history') and agent.chat_history:
+            if agent is not None and hasattr(agent, 'chat_history'):
                 # Update the tracked chat history
                 agent_data["chat_history"] = agent.chat_history
 
-                # Save to memory
+                # Save to memory (save even if empty to track agent existence)
                 history_text = f"Agent chat history for {agent_key}"
                 self.memory.store_short_term(
                     text=history_text,
@@ -353,6 +353,11 @@ def set_state(self, key: str, value: Any) -> None:
         current_state[key] = value
         self.save_state(current_state)
 
+    def increment_state(self, key: str, increment: int = 1, default: int = 0) -> None:
+        """Increment a numeric state value"""
+        current_value = self.get_state(key, default)
+        self.set_state(key, current_value + increment)
+
     def add_memory(self, text: str, memory_type: str = "long", **metadata) -> None:
         """
         Add information to session memory.