diff --git a/src/google/adk/tools/mcp_tool/mcp_session_manager.py b/src/google/adk/tools/mcp_tool/mcp_session_manager.py
index d95d48f282..847bc9f263 100644
--- a/src/google/adk/tools/mcp_tool/mcp_session_manager.py
+++ b/src/google/adk/tools/mcp_tool/mcp_session_manager.py
@@ -38,7 +38,6 @@
   from mcp.client.stdio import stdio_client
   from mcp.client.streamable_http import streamablehttp_client
 except ImportError as e:
-
   if sys.version_info < (3, 10):
     raise ImportError(
         'MCP Tool requires Python 3.10 or above. Please upgrade your Python'
@@ -62,12 +61,15 @@ class StdioConnectionParams(BaseModel):
   server_params: StdioServerParameters
   timeout: float = 5.0
 
+  class Config:
+    arbitrary_types_allowed = True
+
 
 class SseConnectionParams(BaseModel):
   """Parameters for the MCP SSE connection.
 
   See MCP SSE Client documentation for more details.
-  https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/client/sse.py
+  [https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/client/sse.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/client/sse.py)
 
   Attributes:
       url: URL for the MCP SSE server.
@@ -88,7 +90,7 @@ class StreamableHTTPConnectionParams(BaseModel):
   """Parameters for the MCP Streamable HTTP connection.
 
   See MCP Streamable HTTP Client documentation for more details.
-  https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/client/streamable_http.py
+  [https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/client/streamable_http.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/client/streamable_http.py)
 
   Attributes:
       url: URL for the MCP Streamable HTTP server.
@@ -111,12 +113,21 @@ class StreamableHTTPConnectionParams(BaseModel):
 def retry_on_closed_resource(func):
   """Decorator to automatically retry action when MCP session is closed.
 
+  CRITICAL WARNING: This decorator is UNSAFE for non-idempotent operations.
+  Do NOT use with tool calls that create, update, or delete resources as
+  retrying can cause duplicate operations or data corruption.
+
+  Only use with read-only, idempotent operations like list_tools,
+  list_resources, or read_resource.
+
+  Do NOT apply to generic tool execution methods like _run_async_impl.
+
   When MCP session was closed, the decorator will automatically retry the
   action once. The create_session method will handle creating a new session
   if the old one was disconnected.
 
   Args:
-      func: The function to decorate.
+      func: The function to decorate. Must be idempotent and safe to retry.
 
   Returns:
       The decorated function.
@@ -177,11 +188,10 @@ def __init__(
       )
     else:
       self._connection_params = connection_params
-    self._errlog = errlog
 
+    self._errlog = errlog
     # Session pool: maps session keys to (session, exit_stack) tuples
     self._sessions: Dict[str, tuple[ClientSession, AsyncExitStack]] = {}
-
     # Lock to prevent race conditions in session creation
     self._session_lock = asyncio.Lock()
 
@@ -293,6 +303,7 @@ def _create_client(self, merged_headers: Optional[Dict[str, str]] = None):
           ' StdioServerParameters or SseServerParams, but got'
           f' {self._connection_params}'
       )
+
     return client
 
   async def create_session(
@@ -314,7 +325,6 @@ async def create_session(
     """
     # Merge headers once at the beginning
     merged_headers = self._merge_headers(headers)
-
     # Generate session key using merged headers
     session_key = self._generate_session_key(merged_headers)
 
@@ -323,7 +333,6 @@ async def create_session(
       # Check if we have an existing session
       if session_key in self._sessions:
         session, exit_stack = self._sessions[session_key]
-
         # Check if the existing session is still connected
         if not self._is_session_disconnected(session):
           # Session is still good, return it
@@ -369,6 +378,7 @@ async def create_session(
           )
         await asyncio.wait_for(session.initialize(), timeout=timeout_in_seconds)
 
+        await session.initialize()
         # Store session and exit stack in the pool
         self._sessions[session_key] = (session, exit_stack)
         logger.debug('Created new session: %s', session_key)
@@ -404,5 +414,4 @@ async def close(self):
 
 
 SseServerParams = SseConnectionParams
-
 StreamableHTTPServerParams = StreamableHTTPConnectionParams