feat(a2a): add A2AAgent class as an implementation of the agent interface for remote A2A protocol based agents

[awsarron]

Description

Adds an A2AAgent class that makes it simple to consume remote A2A agents and invoke them like any other Strands Agents.

Implements the Protocol in #1126.

Example usage:

from strands import Agent, tool
from strands.agent.a2a_agent import A2AAgent

# Create an A2AAgent to connect to a remote A2A server
a2a_agent = A2AAgent(endpoint="http://localhost:9000")

# Expose the A2AAgent as a tool for our Strands agent to consume
@tool(name="calculator")
def a2a_agent_tool(prompt: str) -> str:
    """Invoke an agent that performs calculations"""
    return str(a2a_agent(prompt))

# Connect the second agent to our A2A agent
agent = Agent(tools=[a2a_agent_tool])

# Invoke the second agent
agent("Show me 10 ^ 6")

print(agent.messages)

Output:

I'll calculate 10^6 for you.
Tool #1: calculator
10^6 = 1,000,000

This represents 10 multiplied by itself 6 times, which equals one million.AgentResult(stop_reason='end_turn', message={'role': 'assistant', 'content': [{'text': '10^6 = 1,000,000\n\nThis represents 10 multiplied by itself 6 times, which equals one million.'}]}, metrics=EventLoopMetrics(cycle_count=2, tool_metrics={'calculator': ToolMetrics(tool={'toolUseId': 'tooluse_FV00wvpRRmK9mYNFo8ax-Q', 'name': 'calculator', 'input': {'prompt': '10^6'}}, call_count=1, success_count=1, error_count=0, total_time=2.747351884841919)}, cycle_durations=[1.717027187347412], traces=[<strands.telemetry.metrics.Trace object at 0x1123c4ec0>, <strands.telemetry.metrics.Trace object at 0x1124e76f0>], accumulated_usage={'inputTokens': 885, 'outputTokens': 99, 'totalTokens': 984}, accumulated_metrics={'latencyMs': 3482}), state={}, interrupts=None, structured_output=None)
>>> 
>>> print(agent.messages)
[{'role': 'user', 'content': [{'text': 'Show me 10 ^ 6'}]}, {'role': 'assistant', 'content': [{'text': "I'll calculate 10^6 for you."}, {'toolUse': {'toolUseId': 'tooluse_FV00wvpRRmK9mYNFo8ax-Q', 'name': 'calculator', 'input': {'prompt': '10^6'}}}]}, {'role': 'user', 'content': [{'toolResult': {'toolUseId': 'tooluse_FV00wvpRRmK9mYNFo8ax-Q', 'status': 'success', 'content': [{'text': '10^6 = 1,000,000\n\nThis represents 10 multiplied by itself 6 times, which equals one million.\n\n'}]}}]}, {'role': 'assistant', 'content': [{'text': '10^6 = 1,000,000\n\nThis represents 10 multiplied by itself 6 times, which equals one million.'}]}]

Standalone invocation of A2AAgent objects also works:

a2a_agent("Show me 10 ^ 6")

AgentResult(stop_reason='end_turn', message={'role': 'assistant', 'content': [{'text': '10^6 = 1,000,000 (one million)\n'}]}, metrics=EventLoopMetrics(cycle_count=0, tool_metrics={}, cycle_durations=[], traces=[], accumulated_usage={'inputTokens': 0, 'outputTokens': 0, 'totalTokens': 0}, accumulated_metrics={'latencyMs': 0}), state={}, interrupts=None, structured_output=None)

Follow-ups:

• Update A2A documentation
• Modify a2a_client tool to use A2AAgent class

Related Issues

#907

Documentation PR

TODO

Type of Change

New feature

Testing

How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli

• I ran hatch run prepare

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• [TODO] I have updated the documentation accordingly
• [TODO] I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• 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.

[codecov]

Codecov Report

❌ Patch coverage is 90.52632% with 9 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/strands/multiagent/a2a/converters.py	82.22%	0 Missing and 8 partials ⚠️
src/strands/agent/a2a_agent.py	98.00%	0 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!

[mkmeral]

Stream async needs to return AgentResult for it to work with graph/swarm https://github.com/strands-agents/sdk-python/blob/main/src/strands/multiagent/graph.py#L810