The SDK should contain a component allowing MCP to be used from native workflow code (i.e. when not using a 3rd-party agent SDK).

For the SDK API, one possibility is that this will be an mcp.ClientSession.

The initial version of this should allow use of existing stdio and http transport MCP servers. Regarding implementation, one possibility is that this will involve a custom transport that responds to tools/list and tools/call calls by making activity calls, making use of an activity-local activity worker to implement stateful sessions, as implemented in #1021. This may be similar to nexus-mcp-python:nexusmcp/workflow_transport.py, adapted to use activities.

Subsequent versions should allow fully durable/fault-tolerant tool calls / client sessions, i.e. making use of durable execution primitives such as workflows exposed as MCP tools. This may involve adding options to make the transport use nexus operations in addition to activities.