feat(a2a): Add exclude_history boolean parameter to A2AClientToolProvider to control whether task.history is included in a2a_send_message responses

[connorjankus]

Description

Add exclude_history boolean parameter to A2AClientToolProvider constructor to control whether task.history is included in a2a_send_message responses.

• Defaults to False to preserve current functionality (history included)
• Set to True to exclude history and reduce payload size by up to ~90% (varies based on response length)
• The history contains many tiny streaming message fragments, but the final complete result is available in artifacts
• Reduces token usage massively in a2a client applications
• Improves latency by a significant amount

Related Issues

Fixes #367

Documentation PR

N/A - Documentation updated in this PR (constructor docstring)

Type of Change

Other (please describe): Enhancement to existing tool

Testing

I have created 2 new unit tests for this functionality which run successfully, and all existing tests still run successfully.

I have manually tested the change by creating two strands agents that communicate using a2a. The first Strands agent (the client agent) uses the A2AClientToolProvider and the a2a_send_message tool to invoke another Strands agent (the server agent). In the server, I am returning a verbose response to the client shown below.

Hello from the A2A Server Agent! This is a hardcoded greeting.
Lorem ipsum dolor sit amet consectetur adipiscing elit. Quisque faucibus ex sapien vitae pellentesque sem placerat. In id cursus mi pretium tellus duis convallis. Tempus leo eu aenean sed diam urna tempor. Pulvinar vivamus fringilla lacus nec metus bibendum egestas. Iaculis massa nisl malesuada lacinia integer nunc posuere. Ut hendrerit semper vel class aptent taciti sociosqu. Ad litora torquent per conubia nostra inceptos himenaeos.

Lorem ipsum dolor sit amet consectetur adipiscing elit. Quisque faucibus ex sapien vitae pellentesque sem placerat. In id cursus mi pretium tellus duis convallis. Tempus leo eu aenean sed diam urna tempor. Pulvinar vivamus fringilla lacus nec metus bibendum egestas. Iaculis massa nisl malesuada lacinia integer nunc posuere. Ut hendrerit semper vel class aptent taciti sociosqu. Ad litora torquent per conubia nostra inceptos himenaeos.

Lorem ipsum dolor sit amet consectetur adipiscing elit. Quisque faucibus ex sapien vitae pellentesque sem placerat. In id cursus mi pretium tellus duis convallis. Tempus leo eu aenean sed diam urna tempor. Pulvinar vivamus fringilla lacus nec metus bibendum egestas. Iaculis massa nisl malesuada lacinia integer nunc posuere. Ut hendrerit semper vel class aptent taciti sociosqu. Ad litora torquent per conubia nostra inceptos himenaeos.

For the results of the tests below, we will be looking at the 'text' field in message.content.toolResult.content. (example message json structure below):

{
  "message": {
    "role": "user",
    "content": [
      {
        "toolResult": {
          "toolUseId": "tooluse_4Ay532SdFk6lgT_-mI6aSQ",
          "status": "success",
          "content": [
            {
              "text": # This is what we will be looking at in the tests
            }
          ]
        }
      }
    ]
  },
  "message_id": 2,
  "redact_message": null,
  "created_at": "2026-01-20T18:55:13.201295+00:00",
  "updated_at": "2026-01-20T18:55:13.201308+00:00"
}

Both tests have the same initial input ("call the downstream agent saying 'Hello'") and the same system prompt

Test 1: The client agent uses A2AClientToolProvider with exclude_history=False and calls the a2a_send_message tool. This replicates the existing behavior of the a2a_send_message tool.

The toolResult content is below (formatted with new lines, history messages truncated because of size), and the content is 17756 characters. This entire content is placed into the agent's context. You can also see that the history is almost entirely useless, given that the combined result is available in the artifacts.

{
    'status': 'success',
    'response': {
        'task': {
            'artifacts': [
                {
                    'artifactId': 'a7e687a7-18b8-46d0-bdb6-78fa8fb3d060',
                    'name': 'agent_response',
                    'parts': [
                        {
                            'kind': 'text',
                            'text': 'Hello from the A2A Server Agent! This is a hardcoded greeting.\n    Lorem ipsum dolor sit amet consectetur adipiscing elit. Quisque faucibus ex sapien vitae pellentesque sem placerat. In id cursus mi pretium tellus duis convallis. Tempus leo eu aenean sed diam urna tempor. Pulvinar vivamus fringilla lacus nec metus bibendum egestas. Iaculis massa nisl malesuada lacinia integer nunc posuere. Ut hendrerit semper vel class aptent taciti sociosqu. Ad litora torquent per conubia nostra inceptos himenaeos.\n\nLorem ipsum dolor sit amet consectetur adipiscing elit. Quisque faucibus ex sapien vitae pellentesque sem placerat. In id cursus mi pretium tellus duis convallis. Tempus leo eu aenean sed diam urna tempor. Pulvinar vivamus fringilla lacus nec metus bibendum egestas. Iaculis massa nisl malesuada lacinia integer nunc posuere. Ut hendrerit semper vel class aptent taciti sociosqu. Ad litora torquent per conubia nostra inceptos himenaeos.\n\nLorem ipsum dolor sit amet consectetur adipiscing elit. Quisque faucibus ex sapien vitae pellentesque sem placerat. In id cursus mi pretium tellus duis convallis. Tempus leo eu aenean sed diam urna tempor. Pulvinar vivamus fringilla lacus nec metus bibendum egestas. Iaculis massa nisl malesuada lacinia integer nunc posuere. Ut hendrerit semper vel class aptent taciti sociosqu. Ad litora torquent per conubia nostra inceptos himenaeos.\n'
                        }
                    ]
                }
            ],
            'contextId': '2f9c4eb7-3546-43bd-b25c-61959c57668f',
            'history': [
                {'contextId': '2f9c4eb7-3546-43bd-b25c-61959c57668f', 'kind': 'message', 'messageId': '1ff55166c92f4e2a9001a93aea10283a', 'parts': [{'kind': 'text', 'text': 'Hello'}], 'role': <Role.user: 'user'>, 'taskId': '0ec89d09-38ed-44dd-badf-1342417f6e1c'},
                {'contextId': '2f9c4eb7-3546-43bd-b25c-61959c57668f', 'kind': 'message', 'messageId': '1106cd7c-b1f9-4751-8093-baee0f8d345e', 'parts': [{'kind': 'text', 'text': 'Hello'}], 'role': <Role.agent: 'agent'>, 'taskId': '0ec89d09-38ed-44dd-badf-1342417f6e1c'},
                {'contextId': '2f9c4eb7-3546-43bd-b25c-61959c57668f', 'kind': 'message', 'messageId': 'fe4a3216-dbf5-48dc-b181-616d7bffdad0', 'parts': [{'kind': 'text', 'text': ' from the A2A Server Agent!'}], 'role': <Role.agent: 'agent'>, 'taskId': '0ec89d09-38ed-44dd-badf-1342417f6e1c'},
                {'contextId': '2f9c4eb7-3546-43bd-b25c-61959c57668f', 'kind': 'message', 'messageId': '9c7ecff2-8993-401f-8574-5868b288138d', 'parts': [{'kind': 'text', 'text': ' This is a hardcoded greeting.'}], 'role': <Role.agent: 'agent'>, 'taskId': '0ec89d09-38ed-44dd-badf-1342417f6e1c'},
                {'contextId': '2f9c4eb7-3546-43bd-b25c-61959c57668f', 'kind': 'message', 'messageId': 'ff38fbbc-18d4-4a3c-b712-47d809fb3db1', 'parts': [{'kind': 'text', 'text': '\\n    '}], 'role': <Role.agent: 'agent'>, 'taskId': '0ec89d09-38ed-44dd-badf-1342417f6e1c'},
                {'contextId': '2f9c4eb7-3546-43bd-b25c-61959c57668f', 'kind': 'message', 'messageId': 'ffe78327-cc83-487f-af08-898d1342ef03', 'parts': [{'kind': 'text', 'text': 'Lorem ipsum dolor sit amet consectetur adipis'}], 'role': <Role.agent: 'agent'>, 'taskId': '0ec89d09-38ed-44dd-badf-1342417f6e1c'},
                {'contextId': '2f9c4eb7-3546-43bd-b25c-61959c57668f', 'kind': 'message', 'messageId': '8e877585-6c60-4cf6-8087-b4c44be50a79', 'parts': [{'kind': 'text', 'text': 'cing elit. Quisque f'}], 'role': <Role.agent: 'agent'>, 'taskId': '0ec89d09-38ed-44dd-badf-1342417f6e1c'},
                # ... (57 more history entries with streaming chunks)
                {'contextId': '2f9c4eb7-3546-43bd-b25c-61959c57668f', 'kind': 'message', 'messageId': '3cfd5f9f-4920-4705-91b9-05af622a326a', 'parts': [{'kind': 'text', 'text': ' himenaeos.'}], 'role': <Role.agent: 'agent'>, 'taskId': '0ec89d09-38ed-44dd-badf-1342417f6e1c'}
            ],
            'id': '0ec89d09-38ed-44dd-badf-1342417f6e1c',
            'kind': 'task',
            'status': {
                'state': <TaskState.completed: 'completed'>,
                'timestamp': '2026-01-21T17:42:46.675477+00:00'
            }
        },
        'update': None
    },
    'message_id': '1ff55166c92f4e2a9001a93aea10283a',
    'target_agent_url': 'http://127.0.0.1:8080'
}

Test 2: The client agent uses A2AClientToolProvider with exclude_history=True and calls the a2a_send_message tool. This excludes the history from the toolResult.

The toolResult content is below (formatted with new lines), and the content is 1910 characters. This is all put into the Agent's context. As you can see, the artifact text includes the result of the a2a task execution, and the history is not needed.

{
    'status': 'success',
    'response': {
        'task': {
            'artifacts': [
                {
                    'artifactId': 'ffc74dfa-c353-44b1-93fc-63364541805a',
                    'name': 'agent_response',
                    'parts': [
                        {
                            'kind': 'text',
                            'text': 'Hello from the A2A Server Agent! This is a hardcoded greeting.\n    Lorem ipsum dolor sit amet consectetur adipiscing elit. Quisque faucibus ex sapien vitae pellentesque sem placerat. In id cursus mi pretium tellus duis convallis. Tempus leo eu aenean sed diam urna tempor. Pulvinar vivamus fringilla lacus nec metus bibendum egestas. Iaculis massa nisl malesuada lacinia integer nunc posuere. Ut hendrerit semper vel class aptent taciti sociosqu. Ad litora torquent per conubia nostra inceptos himenaeos.\n\nLorem ipsum dolor sit amet consectetur adipiscing elit. Quisque faucibus ex sapien vitae pellentesque sem placerat. In id cursus mi pretium tellus duis convallis. Tempus leo eu aenean sed diam urna tempor. Pulvinar vivamus fringilla lacus nec metus bibendum egestas. Iaculis massa nisl malesuada lacinia integer nunc posuere. Ut hendrerit semper vel class aptent taciti sociosqu. Ad litora torquent per conubia nostra inceptos himenaeos.\n\nLorem ipsum dolor sit amet consectetur adipiscing elit. Quisque faucibus ex sapien vitae pellentesque sem placerat. In id cursus mi pretium tellus duis convallis. Tempus leo eu aenean sed diam urna tempor. Pulvinar vivamus fringilla lacus nec metus bibendum egestas. Iaculis massa nisl malesuada lacinia integer nunc posuere. Ut hendrerit semper vel class aptent taciti sociosqu. Ad litora torquent per conubia nostra inceptos himenaeos.\n'
                        }
                    ]
                }
            ],
            'contextId': 'da59f6fc-3492-4312-9a59-d7ab4a9c98c2',
            'id': '09497395-d091-4a68-816d-1dfc941015dd',
            'kind': 'task',
            'status': {
                'state': <TaskState.completed: 'completed'>,
                'timestamp': '2026-01-21T17:57:22.973385+00:00'
            }
        },
        'update': None
    },
    'message_id': 'f6719ad5a3384ecf834fa4892c050462',
    'target_agent_url': 'http://127.0.0.1:8080'
}

• 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
• I have updated the documentation accordingly
• 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.