fix: raise eagerly on importing AgentRegistry if a2a-sdk is missing

- Clean up the unused private _ProtocolType import

Co-authored-by: Sasha Sobran <asobran@google.com>
PiperOrigin-RevId: 913817935

Author: sasha-gitg

src/google/adk/integrations/agent_registry/__init__.py

@@ -12,7 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from .agent_registry import _ProtocolType
 from .agent_registry import AgentRegistry
 
 __all__ = [

src/google/adk/integrations/agent_registry/agent_registry.py

@@ -28,12 +28,7 @@
 from typing import TypedDict
 from urllib.parse import urlparse
 
-from a2a.types import AgentCapabilities
-from a2a.types import AgentCard
-from a2a.types import AgentSkill
-from a2a.types import TransportProtocol as A2ATransport
 from google.adk.agents.readonly_context import ReadonlyContext
-from google.adk.agents.remote_a2a_agent import RemoteA2aAgent
 from google.adk.auth.auth_credential import AuthCredential
 from google.adk.auth.auth_schemes import AuthScheme
 from google.adk.integrations.agent_identity.gcp_auth_provider_scheme import GcpAuthProviderScheme
@@ -49,6 +44,20 @@
 from mcp import StdioServerParameters
 from typing_extensions import override
 
+# pylint: disable=g-import-not-at-top
+try:
+  from a2a.types import AgentCapabilities
+  from a2a.types import AgentCard
+  from a2a.types import AgentSkill
+  from a2a.types import TransportProtocol as A2ATransport
+  from google.adk.agents.remote_a2a_agent import RemoteA2aAgent
+except ImportError as e:
+  raise ImportError(
+      "AgentRegistry requires the 'a2a-sdk' package. "
+      "Please install it using 'pip install google-adk[a2a]'."
+  ) from e
+# pylint: enable=g-import-not-at-top
+
 logger = logging.getLogger("google_adk." + __name__)
 
 AGENT_REGISTRY_BASE_URL = "https://agentregistry.googleapis.com/v1alpha"

tests/unittests/integrations/agent_registry/test_agent_registry.py

@@ -22,8 +22,8 @@
 from google.adk.agents.remote_a2a_agent import RemoteA2aAgent
 from google.adk.auth.auth_credential import AuthCredential
 from google.adk.auth.auth_credential import OAuth2Auth
-from google.adk.integrations.agent_registry import _ProtocolType
 from google.adk.integrations.agent_registry import AgentRegistry
+from google.adk.integrations.agent_registry.agent_registry import _ProtocolType
 from google.adk.telemetry.tracing import GCP_MCP_SERVER_DESTINATION_ID
 from google.adk.tools.mcp_tool.mcp_toolset import McpToolset
 import httpx