Python: [Bug]: async FunctionTool failures bypass max_invocation_exceptions #8277

Description

For an async FunctionTool, exceptions raised inside the coroutine body do not increment invocation_exception_count. As a result, max_invocation_exceptions is never enforced for async tools, although the public documentation describes it as the maximum number of exceptions allowed during invocations.

This can allow a failing async tool to be executed repeatedly after its configured failure budget is exhausted. The separate max_consecutive_errors_per_request loop setting is not equivalent: it is request-scoped and does not enforce the per-tool lifetime limit.

Reproduction

Run against upstream/main at c37de519b:

import asyncio
from agent_framework import FunctionTool

async def always_fails() -> str:
    raise RuntimeError("boom")

async def main() -> None:
    tool = FunctionTool(
        name="always_fails",
        func=always_fails,
        max_invocation_exceptions=1,
    )

    for attempt in range(1, 4):
        try:
            await tool.invoke(skip_parsing=True)
        except Exception as exc:
            print(
                attempt,
                type(exc).__name__,
                tool.invocation_count,
                tool.invocation_exception_count,
            )

asyncio.run(main())

Observed:

1 RuntimeError 1 0
2 RuntimeError 2 0
3 RuntimeError 3 0

For comparison, an equivalent synchronous function produces:

1 RuntimeError 1 1
2 ToolException 1 1

Expected behavior

After the first async invocation failure, the second invocation should raise ToolException when max_invocation_exceptions=1, and invocation_exception_count should report the failure.

Suspected cause

FunctionTool.__call__ catches exceptions only while creating the function result. For an async function, func(...) returns a coroutine successfully; the exception is raised later by await res in _invoke_function, outside the counter's try/except block.

Relevant code:

• python/packages/core/agent_framework/_tools.py:595-632
• python/packages/core/agent_framework/_tools.py:421-422

The repository already supports async tools through FunctionTool.invoke, and the option is not documented as sync-only.

Impact

Any application using async tools with max_invocation_exceptions can exceed the configured failure budget, potentially repeating failing or side-effectful network/database/MCP operations.