fix(telemetry): fix agent span start and end when using Agent.stream_async()

[awsarron]

Description

Fix agent span start and end when using Agent.stream_async()

Related Issues

#118

Documentation PR

N/A

Type of Change

• Bug fix

Testing

• hatch fmt
• hatch run test-lint
• hatch test --all
• hatch run test-integ
• Verified manually with a test script (trace: https://us.cloud.langfuse.com/project/cmaoqkqd901afad07ui6ndt1v/traces/274b27477f1192d0134307ddd3539743?timestamp=2025-05-26T16%3A31%3A17.773Z&display=details):

#!/usr/bin/env python

import asyncio
import logging
import os
from strands import Agent, tool
from strands_tools import calculator, http_request, image_reader

logging.getLogger("strands.telemetry.tracer").setLevel(logging.DEBUG)
logging.basicConfig(
    format="%(levelname)s | %(name)s | %(message)s",
    handlers=[logging.StreamHandler()]
)

os.environ["OTEL_EXPORTER_OTLP_ENDPOINT"] = "https://us.cloud.langfuse.com/api/public/otel"
os.environ["OTEL_EXPORTER_OTLP_HEADERS"] = "Authorization=Basic <REDACTED>"

agent = Agent(
    system_prompt="You are a helpful assistant that provides concise responses.",
    tools=[http_request, calculator, image_reader],
    trace_attributes={
        "session.id": "abc-1234",
        "user.id": "[email protected]",
        "langfuse.tags": [
            "Agent-SDK",
            "Okatank-Project",
            "Observability-Tags",
        ]
    },
    callback_handler=None,
)

async def process_streaming_response():
    agent_stream = agent.stream_async("\u30d5\u30a9\u30fc Describe the image at /Users/arron/strands-samples/01-getting-started/00-first-agent/images/architecture.png")
    async for event in agent_stream:
        print(event)

# Run the agent
asyncio.run(process_streaming_response())

Checklist

• I have read the CONTRIBUTING document
• I have added tests that prove my fix is effective or my feature works
• [-] I have updated the documentation accordingly
• [-] I have added an appropriate example to the documentation to outline the feature
• My changes generate no new warnings
• Any dependent changes have been merged and published

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.