fix(client): ignore the patch version when preferring a 1.0 interface

src/a2a/client/client_factory.py

@@ -38,13 +38,13 @@
 try:
     from a2a.client.transports.grpc import GrpcTransport
 except ImportError:
     GrpcTransport = None  # type: ignore # pyright: ignore
 
 
 try:
     from a2a.compat.v0_3.grpc_transport import CompatGrpcTransport
 except ImportError:
     CompatGrpcTransport = None  # type: ignore # pyright: ignore
 
 logger = logging.getLogger(__name__)
 
@@ -55,6 +55,12 @@
 ]
 
 
+def major_minor(version: str) -> tuple[int, int]:
+    """Returns the `Major.Minor` release of a protocol version."""
+    v = Version(version)
+    return (v.major, v.minor)
+
+
 class ClientFactory:
     """Factory for creating clients that communicate with A2A agents.
 
@@ -229,10 +235,10 @@
         if not candidates:
             return None
 
-        # Prefer interface with version 1.0
-        for i in candidates:
-            if i.protocol_version == PROTOCOL_VERSION_1_0:
-                return i
+        # Prefer interface with version 1.0. Patch versions must not affect
+        # negotiation, so '1.0.0' counts as '1.0'.
+        v1_0 = major_minor(PROTOCOL_VERSION_1_0)
+        v0_3 = major_minor(PROTOCOL_VERSION_0_3)
 
         best_gt_1_0 = None
         best_ge_0_3 = None
@@ -245,10 +251,12 @@
                 continue
 
             try:
-                v = Version(i.protocol_version)
-                if best_gt_1_0 is None and v > Version(PROTOCOL_VERSION_1_0):
+                v = major_minor(i.protocol_version)
+                if v == v1_0:
+                    return i
+                if best_gt_1_0 is None and v > v1_0:
                     best_gt_1_0 = i
-                if best_ge_0_3 is None and v >= Version(PROTOCOL_VERSION_0_3):
+                if best_ge_0_3 is None and v >= v0_3:
                     best_ge_0_3 = i
             except InvalidVersion:
                 pass

tests/client/test_client_factory.py

@@ -115,6 +115,36 @@ def test_client_factory_server_preference(base_agent_card: AgentCard):
     assert client._transport.url == 'http://primary-url.com'  # type: ignore[attr-defined]
 
 
+@pytest.mark.parametrize('v1_version', ['1.0', '1.0.0'])
+def test_client_factory_prefers_1_0_ignoring_patch_version(
+    base_agent_card: AgentCard, v1_version: str
+):
+    """A patch version must not affect protocol negotiation (spec: Versioning)."""
+    del base_agent_card.supported_interfaces[:]
+    base_agent_card.supported_interfaces.extend(
+        [
+            AgentInterface(
+                protocol_binding=TransportProtocol.JSONRPC,
+                url='http://legacy-url.com',
+                protocol_version='0.3.0',
+            ),
+            AgentInterface(
+                protocol_binding=TransportProtocol.JSONRPC,
+                url='http://v1-url.com',
+                protocol_version=v1_version,
+            ),
+        ]
+    )
+    config = ClientConfig(
+        httpx_client=httpx.AsyncClient(),
+        supported_protocol_bindings=[TransportProtocol.JSONRPC],
+    )
+    client = ClientFactory(config).create(base_agent_card)
+
+    assert isinstance(client._transport, JsonRpcTransport)  # type: ignore[attr-defined]
+    assert client._transport.url == 'http://v1-url.com'  # type: ignore[attr-defined]
+
+
 def test_client_factory_no_compatible_transport(base_agent_card: AgentCard):
     """Verify that the factory raises an error if no compatible transport is found."""
     config = ClientConfig(