fix: address review feedback - integer key coercion and in-memory cache serializers

- Convert train_iteration to string keys in crew_agent_executor.py,
  experimental/agent_executor.py, and training_handler.py for JSON compatibility
- Revert file_store.py and agent_card.py back to PickleSerializer since they
  use in-memory caches only (no untrusted deserialization risk)
- Add explanatory comments for why PickleSerializer is safe for in-memory caches

Co-Authored-By: João <joao@crewai.com>

lib/crewai/src/crewai/a2a/utils/agent_card.py

@@ -14,7 +14,7 @@ from typing import TYPE_CHECKING
 from a2a.client.errors import A2AClientHTTPError
 from a2a.types import AgentCapabilities, AgentCard, AgentSkill
 from aiocache import cached  # type: ignore[import-untyped]
-from aiocache.serializers import JsonSerializer  # type: ignore[import-untyped]
+from aiocache.serializers import PickleSerializer  # type: ignore[import-untyped]
 import httpx
 
 from crewai.a2a.auth.client_schemes import APIKeyAuth, HTTPDigestAuth
@@ -220,7 +220,10 @@ def _fetch_agent_card_cached(
     return asyncio.run(coro)
 
 
-@cached(ttl=300, serializer=JsonSerializer())  # type: ignore[untyped-decorator]
+# PickleSerializer is safe here: this is an in-memory cache only.
+# Data never leaves the process, so there is no untrusted deserialization risk.
+# JsonSerializer would break AgentCard (Pydantic model) serialization.
+@cached(ttl=300, serializer=PickleSerializer())  # type: ignore[untyped-decorator]
 async def _afetch_agent_card_cached(
     endpoint: str,
     auth_hash: str,

lib/crewai/src/crewai/agents/crew_agent_executor.py

@@ -8,8 +8,8 @@ from __future__ import annotations
 
 import asyncio
 from collections.abc import Callable
-import contextvars
 from concurrent.futures import ThreadPoolExecutor, as_completed
+import contextvars
 import inspect
 import logging
 from typing import TYPE_CHECKING, Any, Literal, cast
@@ -1599,16 +1599,19 @@ class CrewAgentExecutor(CrewAgentExecutorMixin):
         # Initialize or retrieve agent's training data
         agent_training_data = training_data.get(agent_id, {})
 
+        # Use string key for JSON compatibility (JSON converts int keys to strings)
+        train_key = str(train_iteration)
+
         if human_feedback is not None:
             # Save initial output and human feedback
-            agent_training_data[train_iteration] = {
+            agent_training_data[train_key] = {
                 "initial_output": result.output,
                 "human_feedback": human_feedback,
             }
         else:
             # Save improved output
-            if train_iteration in agent_training_data:
-                agent_training_data[train_iteration]["improved_output"] = result.output
+            if train_key in agent_training_data:
+                agent_training_data[train_key]["improved_output"] = result.output
             else:
                 if self.agent.verbose:
                     self._printer.print(

lib/crewai/src/crewai/experimental/agent_executor.py

@@ -1,9 +1,9 @@
 from __future__ import annotations
 
 import asyncio
-import contextvars
 from collections.abc import Callable, Coroutine
 from concurrent.futures import ThreadPoolExecutor, as_completed
+import contextvars
 from datetime import datetime
 import inspect
 import json
@@ -1492,16 +1492,19 @@ class AgentExecutor(Flow[AgentReActState], CrewAgentExecutorMixin):
         # Initialize or retrieve agent's training data
         agent_training_data = training_data.get(agent_id, {})
 
+        # Use string key for JSON compatibility (JSON converts int keys to strings)
+        train_key = str(train_iteration)
+
         if human_feedback is not None:
             # Save initial output and human feedback
-            agent_training_data[train_iteration] = {
+            agent_training_data[train_key] = {
                 "initial_output": result.output,
                 "human_feedback": human_feedback,
             }
         else:
             # Save improved output
-            if train_iteration in agent_training_data:
-                agent_training_data[train_iteration]["improved_output"] = result.output
+            if train_key in agent_training_data:
+                agent_training_data[train_key]["improved_output"] = result.output
             else:
                 train_error = Text()
                 train_error.append("❌ ", style="red bold")

lib/crewai/src/crewai/utilities/file_store.py

@@ -20,9 +20,12 @@ _file_store: Cache | None = None
 
 try:
     from aiocache import Cache
-    from aiocache.serializers import JsonSerializer
+    from aiocache.serializers import PickleSerializer
 
-    _file_store = Cache(Cache.MEMORY, serializer=JsonSerializer())
+    # PickleSerializer is safe here: this is an in-memory cache only.
+    # Data never leaves the process, so there is no untrusted deserialization risk.
+    # JsonSerializer would break FileInput objects (Pydantic models with IO streams).
+    _file_store = Cache(Cache.MEMORY, serializer=PickleSerializer())
 except ImportError:
     logger.debug(
         "aiocache is not installed. File store features will be disabled. "

lib/crewai/src/crewai/utilities/training_handler.py

@@ -27,7 +27,7 @@ class CrewTrainingHandler(PickleHandler):
         data = self.load()
         if agent_id not in data:
             data[agent_id] = {}
-        data[agent_id][train_iteration] = new_data
+        data[agent_id][str(train_iteration)] = new_data
         self.save(data)
 
     def clear(self) -> None: