fix: use endpoint-scoped task IDs for A2A delegations

This fixes issue #4166 where delegating to a second A2A agent fails
because the task_id from the first agent is in 'completed' state.

The fix introduces endpoint-scoped task ID storage in task.config
using a2a_task_ids_by_endpoint dictionary. This ensures that:
- Each A2A endpoint gets its own task_id
- Multi-turn conversations with the same endpoint reuse the task_id
- Sequential delegations to different endpoints use separate task_ids

Added tests to verify:
- Sequential delegation to multiple endpoints uses separate task IDs
- Multi-turn conversations with same endpoint reuse task IDs
- Endpoint-scoped task IDs are properly persisted to task.config

Co-Authored-By: João <joao@crewai.com>

lib/crewai/src/crewai/a2a/wrapper.py

@@ -531,10 +531,17 @@ def _delegate_to_a2a(
     agent_config = next(filter(lambda x: x.endpoint == agent_id, a2a_agents))
     task_config = task.config or {}
     context_id = task_config.get("context_id")
-    task_id_config = task_config.get("task_id")
     metadata = task_config.get("metadata")
     extensions = task_config.get("extensions")
 
+    # Use endpoint-scoped task IDs to prevent reusing task IDs across different A2A agents
+    # This fixes the issue where delegating to a second A2A agent fails because the task_id
+    # from the first agent is in "completed" state
+    a2a_task_ids_by_endpoint: dict[str, str] = task_config.get(
+        "a2a_task_ids_by_endpoint", {}
+    )
+    task_id_config = a2a_task_ids_by_endpoint.get(agent_id)
+
     reference_task_ids = task_config.get("reference_task_ids", [])
 
     if original_task_description is None:
@@ -576,6 +583,8 @@ def _delegate_to_a2a(
                 latest_message = conversation_history[-1]
                 if latest_message.task_id is not None:
                     task_id_config = latest_message.task_id
+                    # Store the task_id scoped to this endpoint for multi-turn conversations
+                    a2a_task_ids_by_endpoint[agent_id] = task_id_config
                 if latest_message.context_id is not None:
                     context_id = latest_message.context_id
 
@@ -584,13 +593,15 @@ def _delegate_to_a2a(
                     a2a_result["status"] == "completed"
                     and agent_config.trust_remote_completion_status
                 ):
+                    if task.config is None:
+                        task.config = {}
+                    # Persist endpoint-scoped task IDs for future delegations
+                    task.config["a2a_task_ids_by_endpoint"] = a2a_task_ids_by_endpoint
                     if (
                         task_id_config is not None
                         and task_id_config not in reference_task_ids
                     ):
                         reference_task_ids.append(task_id_config)
-                        if task.config is None:
-                            task.config = {}
                         task.config["reference_task_ids"] = reference_task_ids
 
                     result_text = a2a_result.get("result", "")

lib/crewai/tests/agents/test_a2a_multiple_endpoints.py

@@ -0,0 +1,314 @@
+"""Test A2A delegation to multiple endpoints sequentially.
+
+This test file covers the bug fix for issue #4166 where delegating to a second
+A2A agent fails because the task_id from the first agent is in "completed" state.
+"""
+
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from crewai.a2a.config import A2AConfig
+
+try:
+    from a2a.types import Message, Part, Role, TextPart
+
+    A2A_SDK_INSTALLED = True
+except ImportError:
+    A2A_SDK_INSTALLED = False
+
+
+@pytest.mark.skipif(not A2A_SDK_INSTALLED, reason="Requires a2a-sdk to be installed")
+def test_sequential_delegation_to_multiple_endpoints_uses_separate_task_ids():
+    """When delegating to multiple A2A endpoints sequentially, each should get a unique task_id.
+
+    This test verifies the fix for issue #4166 where the second A2A delegation
+    fails with 'Task is in terminal state: completed' because the task_id from
+    the first delegation was being reused.
+    """
+    from crewai.a2a.wrapper import _delegate_to_a2a
+    from crewai import Agent, Task
+
+    # Configure agent with two A2A endpoints
+    a2a_configs = [
+        A2AConfig(
+            endpoint="http://endpoint-a.com",
+            trust_remote_completion_status=True,
+        ),
+        A2AConfig(
+            endpoint="http://endpoint-b.com",
+            trust_remote_completion_status=True,
+        ),
+    ]
+
+    agent = Agent(
+        role="test manager",
+        goal="coordinate",
+        backstory="test",
+        a2a=a2a_configs,
+    )
+
+    task = Task(description="test", expected_output="test", agent=agent)
+
+    # First delegation to endpoint A
+    class MockResponseA:
+        is_a2a = True
+        message = "Please help with task A"
+        a2a_ids = ["http://endpoint-a.com/"]
+
+    # Second delegation to endpoint B
+    class MockResponseB:
+        is_a2a = True
+        message = "Please help with task B"
+        a2a_ids = ["http://endpoint-b.com/"]
+
+    task_ids_used = []
+
+    def mock_execute_a2a_delegation(**kwargs):
+        """Track the task_id used for each delegation."""
+        task_ids_used.append(kwargs.get("task_id"))
+        endpoint = kwargs.get("endpoint")
+
+        # Create a mock message with a task_id
+        mock_message = MagicMock()
+        mock_message.task_id = f"task-id-for-{endpoint}"
+        mock_message.context_id = None
+
+        return {
+            "status": "completed",
+            "result": f"Done by {endpoint}",
+            "history": [mock_message],
+        }
+
+    with (
+        patch(
+            "crewai.a2a.wrapper.execute_a2a_delegation",
+            side_effect=mock_execute_a2a_delegation,
+        ) as mock_execute,
+        patch("crewai.a2a.wrapper._fetch_agent_cards_concurrently") as mock_fetch,
+    ):
+        mock_card_a = MagicMock()
+        mock_card_a.name = "Agent A"
+        mock_card_b = MagicMock()
+        mock_card_b.name = "Agent B"
+        mock_fetch.return_value = (
+            {
+                "http://endpoint-a.com/": mock_card_a,
+                "http://endpoint-b.com/": mock_card_b,
+            },
+            {},
+        )
+
+        # First delegation to endpoint A
+        result_a = _delegate_to_a2a(
+            self=agent,
+            agent_response=MockResponseA(),
+            task=task,
+            original_fn=lambda *args, **kwargs: "fallback",
+            context=None,
+            tools=None,
+            agent_cards={
+                "http://endpoint-a.com/": mock_card_a,
+                "http://endpoint-b.com/": mock_card_b,
+            },
+            original_task_description="test",
+        )
+
+        assert result_a == "Done by http://endpoint-a.com/"
+
+        # Verify the endpoint-scoped task IDs are stored in task.config
+        assert task.config is not None
+        assert "a2a_task_ids_by_endpoint" in task.config
+        assert (
+            task.config["a2a_task_ids_by_endpoint"]["http://endpoint-a.com/"]
+            == "task-id-for-http://endpoint-a.com/"
+        )
+
+        # Second delegation to endpoint B
+        result_b = _delegate_to_a2a(
+            self=agent,
+            agent_response=MockResponseB(),
+            task=task,
+            original_fn=lambda *args, **kwargs: "fallback",
+            context=None,
+            tools=None,
+            agent_cards={
+                "http://endpoint-a.com/": mock_card_a,
+                "http://endpoint-b.com/": mock_card_b,
+            },
+            original_task_description="test",
+        )
+
+        assert result_b == "Done by http://endpoint-b.com/"
+
+        # Verify that the second delegation used a different (None) task_id
+        # The first call should have task_id=None (no prior task_id for endpoint A)
+        # The second call should also have task_id=None (no prior task_id for endpoint B)
+        assert len(task_ids_used) == 2
+        assert task_ids_used[0] is None  # First delegation to endpoint A
+        assert task_ids_used[1] is None  # Second delegation to endpoint B (not reusing A's task_id)
+
+
+@pytest.mark.skipif(not A2A_SDK_INSTALLED, reason="Requires a2a-sdk to be installed")
+def test_multi_turn_conversation_with_same_endpoint_reuses_task_id():
+    """Multi-turn conversations with the same endpoint should reuse the task_id.
+
+    This test ensures that the fix for issue #4166 doesn't break multi-turn
+    conversations with the same endpoint. When trust_remote_completion_status=True,
+    the task_id should be stored and reused for subsequent calls to the same endpoint.
+    """
+    from crewai.a2a.wrapper import _delegate_to_a2a
+    from crewai import Agent, Task
+
+    a2a_config = A2AConfig(
+        endpoint="http://test-endpoint.com",
+        trust_remote_completion_status=True,
+    )
+
+    agent = Agent(
+        role="test manager",
+        goal="coordinate",
+        backstory="test",
+        a2a=a2a_config,
+    )
+
+    task = Task(description="test", expected_output="test", agent=agent)
+
+    class MockResponse:
+        is_a2a = True
+        message = "Please help"
+        a2a_ids = ["http://test-endpoint.com/"]
+
+    task_ids_used = []
+
+    def mock_execute_a2a_delegation(**kwargs):
+        """Track the task_id used for each call."""
+        task_ids_used.append(kwargs.get("task_id"))
+
+        # Create a mock message with a task_id
+        mock_message = MagicMock()
+        mock_message.task_id = "persistent-task-id"
+        mock_message.context_id = None
+
+        return {
+            "status": "completed",
+            "result": "Done",
+            "history": [mock_message],
+        }
+
+    with (
+        patch(
+            "crewai.a2a.wrapper.execute_a2a_delegation",
+            side_effect=mock_execute_a2a_delegation,
+        ),
+        patch("crewai.a2a.wrapper._fetch_agent_cards_concurrently") as mock_fetch,
+    ):
+        mock_card = MagicMock()
+        mock_card.name = "Test"
+        mock_fetch.return_value = ({"http://test-endpoint.com/": mock_card}, {})
+
+        # First delegation
+        _delegate_to_a2a(
+            self=agent,
+            agent_response=MockResponse(),
+            task=task,
+            original_fn=lambda *args, **kwargs: "fallback",
+            context=None,
+            tools=None,
+            agent_cards={"http://test-endpoint.com/": mock_card},
+            original_task_description="test",
+        )
+
+        # Verify the task_id was stored in the endpoint-scoped dictionary
+        assert task.config is not None
+        assert "a2a_task_ids_by_endpoint" in task.config
+        stored_task_id = task.config["a2a_task_ids_by_endpoint"].get(
+            "http://test-endpoint.com/"
+        )
+        assert stored_task_id == "persistent-task-id"
+
+        # Second delegation to the SAME endpoint should use the stored task_id
+        _delegate_to_a2a(
+            self=agent,
+            agent_response=MockResponse(),
+            task=task,
+            original_fn=lambda *args, **kwargs: "fallback",
+            context=None,
+            tools=None,
+            agent_cards={"http://test-endpoint.com/": mock_card},
+            original_task_description="test",
+        )
+
+        # Verify that the second call used the stored task_id
+        assert len(task_ids_used) == 2
+        # First call should have no task_id (new conversation)
+        assert task_ids_used[0] is None
+        # Second call should reuse the task_id from the first call
+        assert task_ids_used[1] == "persistent-task-id"
+
+
+@pytest.mark.skipif(not A2A_SDK_INSTALLED, reason="Requires a2a-sdk to be installed")
+def test_endpoint_scoped_task_ids_are_persisted_to_task_config():
+    """Verify that endpoint-scoped task IDs are properly persisted to task.config."""
+    from crewai.a2a.wrapper import _delegate_to_a2a
+    from crewai import Agent, Task
+
+    a2a_config = A2AConfig(
+        endpoint="http://test-endpoint.com",
+        trust_remote_completion_status=True,
+    )
+
+    agent = Agent(
+        role="test manager",
+        goal="coordinate",
+        backstory="test",
+        a2a=a2a_config,
+    )
+
+    task = Task(description="test", expected_output="test", agent=agent)
+
+    class MockResponse:
+        is_a2a = True
+        message = "Please help"
+        a2a_ids = ["http://test-endpoint.com/"]
+
+    def mock_execute_a2a_delegation(**kwargs):
+        mock_message = MagicMock()
+        mock_message.task_id = "unique-task-id-123"
+        mock_message.context_id = None
+
+        return {
+            "status": "completed",
+            "result": "Done",
+            "history": [mock_message],
+        }
+
+    with (
+        patch(
+            "crewai.a2a.wrapper.execute_a2a_delegation",
+            side_effect=mock_execute_a2a_delegation,
+        ),
+        patch("crewai.a2a.wrapper._fetch_agent_cards_concurrently") as mock_fetch,
+    ):
+        mock_card = MagicMock()
+        mock_card.name = "Test"
+        mock_fetch.return_value = ({"http://test-endpoint.com/": mock_card}, {})
+
+        _delegate_to_a2a(
+            self=agent,
+            agent_response=MockResponse(),
+            task=task,
+            original_fn=lambda *args, **kwargs: "fallback",
+            context=None,
+            tools=None,
+            agent_cards={"http://test-endpoint.com/": mock_card},
+            original_task_description="test",
+        )
+
+        # Verify the endpoint-scoped task IDs are stored
+        assert task.config is not None
+        assert "a2a_task_ids_by_endpoint" in task.config
+        assert (
+            task.config["a2a_task_ids_by_endpoint"]["http://test-endpoint.com/"]
+            == "unique-task-id-123"
+        )