a2a workflows fix (#1860)

python/packages/a2a/agent_framework_a2a/_agent.py

@@ -127,7 +127,21 @@ class A2AAgent(BaseAgent):
         )
         factory = ClientFactory(config)
         interceptors = [auth_interceptor] if auth_interceptor is not None else None
-        self.client = factory.create(agent_card, interceptors=interceptors)  # type: ignore
+
+        # Attempt transport negotiation with the provided agent card
+        try:
+            self.client = factory.create(agent_card, interceptors=interceptors)  # type: ignore
+        except Exception as transport_error:
+            # Transport negotiation failed - fall back to minimal agent card with JSONRPC
+            fallback_card = minimal_agent_card(agent_card.url, [TransportProtocol.jsonrpc])
+            try:
+                self.client = factory.create(fallback_card, interceptors=interceptors)  # type: ignore
+            except Exception as fallback_error:
+                raise RuntimeError(
+                    f"A2A transport negotiation failed. "
+                    f"Primary error: {transport_error}. "
+                    f"Fallback error: {fallback_error}"
+                ) from transport_error
 
     async def __aenter__(self) -> "A2AAgent":
         """Async context manager entry."""

python/packages/a2a/tests/test_a2a_agent.py

@@ -2,10 +2,22 @@
 
 from collections.abc import AsyncIterator
 from typing import Any
-from unittest.mock import AsyncMock, MagicMock
+from unittest.mock import AsyncMock, MagicMock, patch
 from uuid import uuid4
 
-from a2a.types import Artifact, DataPart, FilePart, FileWithUri, Message, Part, Task, TaskState, TaskStatus, TextPart
+from a2a.types import (
+    AgentCard,
+    Artifact,
+    DataPart,
+    FilePart,
+    FileWithUri,
+    Message,
+    Part,
+    Task,
+    TaskState,
+    TaskStatus,
+    TextPart,
+)
 from a2a.types import Role as A2ARole
 from agent_framework import (
     AgentRunResponse,
@@ -515,3 +527,30 @@ def test_auth_interceptor_parameter() -> None:
     # Verify the agent was created successfully
     assert agent.name == "test-agent"
     assert agent.client is not None
+
+
+def test_transport_negotiation_both_fail() -> None:
+    """Test that RuntimeError is raised when both primary and fallback transport negotiation fail."""
+    # Create a mock agent card
+    mock_agent_card = MagicMock(spec=AgentCard)
+    mock_agent_card.url = "http://test-agent.example.com"
+
+    # Mock the factory to simulate both primary and fallback failures
+    mock_factory = MagicMock()
+
+    # Both calls to factory.create() fail
+    primary_error = Exception("no compatible transports found")
+    fallback_error = Exception("fallback also failed")
+    mock_factory.create.side_effect = [primary_error, fallback_error]
+
+    with (
+        patch("agent_framework_a2a._agent.ClientFactory", return_value=mock_factory),
+        patch("agent_framework_a2a._agent.minimal_agent_card"),
+        patch("agent_framework_a2a._agent.httpx.AsyncClient"),
+        raises(RuntimeError, match="A2A transport negotiation failed"),
+    ):
+        # Attempt to create A2AAgent - should raise RuntimeError
+        A2AAgent(
+            name="test-agent",
+            agent_card=mock_agent_card,
+        )