lazy initialize the session upon stdio client initializes

mcp_proxy_for_aws/server.py

@@ -84,7 +84,7 @@ async def setup_mcp_mode(local_mcp: FastMCP, args) -> None:
     transport = create_transport_with_sigv4(
         args.endpoint, service, region, metadata, timeout, profile
     )
-    async with Client(transport=transport) as client:
+    async with Client(transport=transport, auto_initialize=False) as client:
         # Create proxy with the transport
         proxy = FastMCP.as_proxy(client)
         add_logging_middleware(proxy, args.log_level)

pyproject.toml

@@ -16,7 +16,7 @@ description = "MCP Proxy for AWS"
 readme = "README.md"
 requires-python = ">=3.10,<3.14"
 dependencies = [
-    "fastmcp>=2.13.0.2",
+    "fastmcp>=2.13.1",
     "boto3>=1.34.0",
     "botocore>=1.34.0",
 ]

tests/integ/mcp/simple_mcp_server/mcp_server.py

@@ -79,8 +79,12 @@ async def elicit_for_my_name(elicitation_expected: str, ctx: Context):
 @mcp.tool
 def echo_metadata(ctx: Context):
     """MCP Tool that echoes back the _meta field from the request."""
-    meta = ctx.request_context.meta
-    return {'received_meta': meta}
+    if ctx.request_context:
+        meta = ctx.request_context.meta
+        return {'received_meta': meta}
+    else:
+        # should not happen, trying to make typechecker happy
+        raise RuntimeError('MCP tool invoked before session is initialized')
 
 
 #### Server Setup

tests/unit/test_server.py

@@ -99,7 +99,7 @@ async def test_setup_mcp_mode(
         assert call_args[0][3] == {'AWS_REGION': 'us-east-1'}  # metadata
         # call_args[0][4] is the Timeout object
         assert call_args[0][5] is None  # profile
-        mock_client_class.assert_called_once_with(transport=mock_transport)
+        mock_client_class.assert_called_once_with(transport=mock_transport, auto_initialize=False)
         mock_as_proxy.assert_called_once_with(mock_client)
         mock_add_filtering.assert_called_once_with(mock_proxy, True)
         mock_add_retry.assert_called_once_with(mock_proxy, 1)
@@ -173,7 +173,7 @@ async def test_setup_mcp_mode_no_retries(
         }  # metadata
         # call_args[0][4] is the Timeout object
         assert call_args[0][5] == 'test-profile'  # profile
-        mock_client_class.assert_called_once_with(transport=mock_transport)
+        mock_client_class.assert_called_once_with(transport=mock_transport, auto_initialize=False)
         mock_as_proxy.assert_called_once_with(mock_client)
         mock_add_filtering.assert_called_once_with(mock_proxy, False)
         mock_proxy.run_async.assert_called_once()