Python: Foundry Toolbox MCP proxy rejects MCPStreamableHTTPTool.call_tool() from custom tool code — "No tool config matches tool name"

[smdp2000ofc]

Description

Calling MCPStreamableHTTPTool.call_tool() directly from Python code inside a custom @tool function fails with:

McpError: No tool config matches tool name 'WorkIQSharePoint.readSmallBinaryFile'. Provide matching _meta.tools entries.

The exact same tool succeeds when the framework's executor pipeline invokes it (i.e., when the LLM decides to call it as a tool). This means:

• ✅ LLM → framework executor → call_tool() → works
• ❌ Custom @tool Python code → toolbox_ref.call_tool() → fails

This is a regression — the same code was working in production until recently (around May 10-12, 2026). No SDK or agent code was changed — the Foundry Toolbox MCP server-side appears to have started enforcing _meta.tool_configuration validation on tools/call requests.

Steps to Reproduce

1. Create a Foundry Toolbox with MCP tools (e.g., WorkIQ SharePoint connector)
2. Connect via MCPStreamableHTTPTool with proper auth headers and Foundry-Features: Toolboxes=V1Preview
3. Register the toolbox as a tool on an Agent
4. Inside a custom @tool function, call toolbox_ref.call_tool("ServerLabel.ToolName", arg=value)

from agent_framework import Agent, MCPStreamableHTTPTool, tool
import httpx

# Setup toolbox connection
toolbox = MCPStreamableHTTPTool(
    name="my-toolbox",
    url=f"{project_endpoint}/toolboxes/my-toolbox/versions/1/mcp?api-version=v1",
    http_client=httpx.AsyncClient(
        auth=MyAuth(token_provider),
        headers={"Foundry-Features": "Toolboxes=V1Preview"},
    ),
    load_prompts=False,
)

# Custom tool that calls MCP toolbox directly
@tool(approval_mode="never_require")
async def save_file_to_storage(document_library_id: str, file_id: str) -> dict:
    # This FAILS:
    result = await toolbox.call_tool(
        "WorkIQSharePoint.readSmallBinaryFile",
        documentLibraryId=document_library_id,
        fileId=file_id,
    )
    # ... process result and save to storage ...

agent = Agent(client=client, tools=[toolbox, save_file_to_storage])

Error

mcp.shared.exceptions.McpError: No tool config matches tool name 'WorkIQSharePoint.readSmallBinaryFile'. Provide matching _meta.tools entries.

The error originates from the Foundry Toolbox MCP server (POST .../toolboxes/.../mcp), not from the SDK.

Root Cause Analysis

Looking at MCPTool.call_tool() in _mcp.py:

otel_meta = _inject_otel_into_mcp_meta()
result = await self.session.call_tool(tool_name, arguments=filtered_kwargs, meta=otel_meta)

The meta parameter only contains OpenTelemetry trace context. It does not include the _meta.tool_configuration block that the Foundry Toolbox MCP proxy now requires.

When the framework's executor pipeline calls a tool (LLM → executor → call_tool), the _meta.tool_configuration is somehow injected (likely by the responses API or the executor's function invocation pipeline). But direct call_tool() from code bypasses this.

Expected Behavior

MCPStreamableHTTPTool.call_tool() should work from custom tool code. The _meta.tool_configuration entries (available from tools/list response at connect time) should be automatically injected into the meta parameter of session.call_tool().

Actual Behavior

The Foundry Toolbox MCP proxy rejects the call because _meta.tool_configuration is missing from the request.

Environment

• agent-framework-core: 1.2.2
• agent-framework-foundry: 1.2.2
• agent-framework-devui: 1.0.0b260304
• Python: 3.12.10
• OS: Windows 11
• MCP protocol version: 2025-11-25
• Foundry Toolbox endpoint: {project_endpoint}/toolboxes/{name}/versions/{version}/mcp?api-version=v1