fix(adapters): wrap redacted MCP output in CallToolResult

When mcp_check_output returns redacted_data, the interceptor was
returning a plain str. langchain-mcp-adapters expects MCPToolCallResult
(CallToolResult | ToolMessage | Command) and calls .content on the
return value, causing AttributeError at runtime.

Now wraps the redacted string in a CallToolResult with a single
TextContent block, which is the correct return type for the interceptor
protocol. Also adds mcp>=1.0.0 as a new 'langgraph' optional extra and
to dev dependencies, with a lazy import that surfaces a clear error
message if mcp is not installed.

Fixes #119

Author: gzak

axonflow/adapters/langgraph.py

@@ -538,6 +538,15 @@ def mcp_tool_interceptor(
             An async callable ``(request, handler) -> result`` suitable for
             ``MultiServerMCPClient(tool_interceptors=[...])``.
         """
+        try:
+            from mcp.types import CallToolResult, TextContent  # noqa: PLC0415
+        except ImportError as exc:
+            msg = (
+                "The 'mcp' package is required to use mcp_tool_interceptor. "
+                "Install it with: pip install 'axonflow[langgraph]'"
+            )
+            raise ImportError(msg) from exc
+
         opts = options or MCPInterceptorOptions()
 
         def _default_connector_type(request: Any) -> str:
@@ -574,7 +583,9 @@ async def _interceptor(request: Any, handler: Callable[..., Any]) -> Any:
                     output_check.block_reason or "Tool result blocked by policy"
                 )
             if output_check.redacted_data is not None:
-                return output_check.redacted_data
+                return CallToolResult(
+                    content=[TextContent(type="text", text=output_check.redacted_data)]
+                )
 
             return result
 

pyproject.toml

@@ -52,6 +52,7 @@ dev = [
     "black>=23.0.0",
     "isort>=5.12.0",
     "pre-commit>=3.0.0",
+    "mcp>=1.0.0",
 ]
 docs = [
     "sphinx>=7.0.0",
@@ -61,9 +62,11 @@ docs = [
 ]
 openai = ["openai>=1.0.0"]
 anthropic = ["anthropic>=0.18.0"]
+langgraph = ["mcp>=1.0.0"]
 all = [
     "openai>=1.0.0",
     "anthropic>=0.18.0",
+    "mcp>=1.0.0",
 ]
 
 [project.urls]
@@ -167,6 +170,7 @@ show_column_numbers = true
 module = "tests.*"
 disallow_untyped_defs = false
 
+
 [tool.pytest.ini_options]
 asyncio_mode = "auto"
 testpaths = ["tests"]

tests/test_langgraph_adapter.py

@@ -7,6 +7,7 @@
 from unittest.mock import AsyncMock, MagicMock
 
 import pytest
+from mcp.types import CallToolResult, TextContent
 
 from axonflow import AxonFlow
 from axonflow.adapters.langgraph import AxonFlowLangGraphAdapter, MCPInterceptorOptions
@@ -192,7 +193,10 @@ async def test_returns_redacted_data_when_present(
 
         result = await adapter.mcp_tool_interceptor()(MagicMock(), handler)
 
-        assert result == "[REDACTED]"
+        assert isinstance(result, CallToolResult)
+        assert len(result.content) == 1
+        assert isinstance(result.content[0], TextContent)
+        assert result.content[0].text == "[REDACTED]"
 
     @pytest.mark.asyncio
     async def test_returns_original_result_when_no_redaction(