Support async tool functions

[wu-changxing]

Problem

Tool executor (tool_executor.py:195) only supports sync functions:

result = tool_func(**tool_args)

This blocks us from using async libraries as tools (browser-use CDP, async HTTP clients, async database drivers, etc). Currently the only workaround is wrapping every async call with asyncio.run() inside each tool method — ugly and error-prone.

Proposed Change

One line change in execute_single_tool():

import asyncio, inspect

if inspect.iscoroutinefunction(tool_func):
    result = asyncio.run(tool_func(**tool_args))
else:
    result = tool_func(**tool_args)

No changes needed in agent.py, tool_factory.py, or tool_registry.py. The agent loop stays sync — we just bridge to async at the execution point.

Why

Immediate use case: wrap browser-use BrowserSession as a ConnectOnion tool (useful_tools/browser_use.py). browser-use is fully async CDP-based. With async tool support, we can write clean tools like:

class BrowserUse:
    async def navigate(self, url: str) -> str:
        event = self.session.event_bus.dispatch(NavigateToUrlEvent(url=url))
        await event
        return f"Navigated to {url}"

Instead of wrapping every method with asyncio.run().

Scope

• connectonion/core/tool_executor.py — detect coroutine, run with asyncio.run()
• connectonion/core/tool_factory.py — no change needed (signature inspection works the same for async functions)
• Tests: add one test with an async tool function