fix(tools): prevent tool_runner from exiting when server_tool_use blocks are present

[tao-to-python]

Description

Fixes premature exit of tool_runner when server-side tools are used alongside client tools, as reported in #1170.

Problem

When using client.beta.messages.tool_runner() with server-side tools like web_search or web_fetch, the API responds with server_tool_use blocks and stop_reason="pause_turn". However, _generate_tool_call_response() only filters for block.type == "tool_use":

tool_use_blocks = [block for block in content if block.type == "tool_use"]
if not tool_use_blocks:
    return None  # exits the runner

server_tool_use blocks have a different type, so the list is empty, None is returned, and the runner exits before the server can return results.

Solution

When no client tool_use blocks are found, check for server_tool_use blocks. If present, return an empty user message to continue the loop:

has_server_tools = any(block.type == "server_tool_use" for block in content)
if has_server_tools:
    return {"role": "user", "content": []}

Applied to both sync and async paths.

Changes

File	Change
src/anthropic/lib/tools/_beta_runner.py	Handle server_tool_use in sync + async

Fixes #1170