feat: prefer stateful runtime for mcp content access

src/wf_mcp/sdk/__init__.py

@@ -1,3 +1,8 @@
-from wf_sources_mcp.sdk import BackendAdapter, McpSdkAdapter, ToolCallResult
+from wf_sources_mcp.sdk import (
+    BackendAdapter,
+    McpSdkAdapter,
+    StatefulMcpRuntime,
+    ToolCallResult,
+)
 
-__all__ = ["BackendAdapter", "McpSdkAdapter", "ToolCallResult"]
+__all__ = ["BackendAdapter", "McpSdkAdapter", "StatefulMcpRuntime", "ToolCallResult"]

src/wf_mcp/sdk/base.py

@@ -5,9 +5,10 @@ Canonical implementation lives in `wf_sources_mcp.sdk`.
 
 from __future__ import annotations
 
-from wf_sources_mcp.sdk import BackendAdapter, ToolCallResult
+from wf_sources_mcp.sdk import BackendAdapter, StatefulMcpRuntime, ToolCallResult
 
 __all__ = [
     "BackendAdapter",
+    "StatefulMcpRuntime",
     "ToolCallResult",
 ]