[BUG] Wrong toolUseId when using gemini-2.5-flash

[AirswitchAsa]

Checks

• [x] I have updated to the lastest minor and patch version of Strands
• [x] I have checked the documentation and this is not expected behavior
• [x] I have searched ./issues and there are no duplicates of my issue

Strands Version

1.17.0

Python Version

3.13.2

Operating System

MacOS 15.6.1 (24G90)

Installation Method

pip

Steps to Reproduce

1. have environment set up. I have an example here
2. run the following script

import asyncio
import random

from strands import Agent, tool
from strands.models.gemini import GeminiModel

model: GeminiModel = GeminiModel(
    client_args={"api_key": os.getenv("GOOGLE_AI_API_KEY")},
    model_id="gemini-2.5-flash",
)


@tool
async def call_api() -> str:
    """Call API asynchronously."""

    await asyncio.sleep(3)  # simulated api call
    return f"API result: {random.randint(1, 1000)}"

agent = Agent(tools=[call_api], model=model, callback_handler=None, name="gemini_agent")

# Async function that iterators over streamed agent events
async def process_streaming_response(agent: Agent) -> None:
    agent_stream = agent.stream_async("Can you call my API twice?")
    print(f"Starting to stream events for {agent.name}")
    async for event in agent_stream:
        print(event)
    print(f"Finished streaming events for {agent.name}")


asyncio.run(process_streaming_response(agent))

Expected Behavior

unique toolUseId named in the format tooluse_{identifier}

Actual Behavior

call_api being shown as the toolUseId instead of something like tooluse_{identifier}, like below:

{"message": {"role": "assistant", "content": [{"toolUse": {"toolUseId": "call_api", "name": "call_api", "input": {}}}]}}

Additional Context

No response

Possible Solution

No response

Related Issues

No response

[AirswitchAsa]

okay I think this is probably the reason

# Note: toolUseId is the only identifier available in a tool result. However, Gemini requires
#       that name be set in the equivalent FunctionResponse type. Consequently, we assign
#       function name to toolUseId in our tool use block. And another reason, function_call is
#       not guaranteed to have id populated.

https://github.com/strands-agents/sdk-python/blob/main/src/strands/models/gemini.py#L267-L270 this is resulting in in-differentiable tool uses if a tool gets used twice.

I think we can store a map<tooluseid, function_name> internally to expose the tooluseid to the user but function name to gemini in FunctionResponse. I am not familiar with the codebase, but willing to contribute

[AirswitchAsa]

I tried to follow all the guidelines and created #1201

If you find anything inappropriate with the PR, feel free to make changes or dispose it. Thanks.

[pgrayy]

Left a comment on the PR.

[AirswitchAsa]

@cagataycali sorry I have not finished the PR that I opened for merging - I saw that you have also created a PR to fix this issue in the similar way, should I close mine in this case?

[cagataycali]

Hi Qian! @AirswitchAsa

The PR you see in details is automatically created during my benchmarks. Please do continue with your contribution!