feat(sdk): add streaming extensions and response accumulator

apps/adk-cli/src/kagenti_cli/api.py

@@ -16,7 +16,8 @@
 import httpx
 import openai
 import pydantic
-from a2a.client import A2AClientError, Client, ClientConfig, ClientFactory
+from a2a.client import A2AClientError, Client, ClientCallContext, ClientConfig, ClientFactory
+from a2a.extensions.common import HTTP_EXTENSION_HEADER
 from a2a.types import AgentCard
 from kagenti_adk.platform.context import ContextToken
 from google.protobuf.json_format import MessageToDict
@@ -131,16 +132,26 @@ class OpenAPISchema(pydantic.BaseModel):
         return None
 
 
+def make_extension_context(extensions: list[str] | None = None) -> ClientCallContext | None:
+    """Create a ClientCallContext with extension URIs as service parameters."""
+    if not extensions:
+        return None
+    return ClientCallContext(service_parameters={HTTP_EXTENSION_HEADER: ",".join(extensions)})
+
+
 @asynccontextmanager
-async def a2a_client(agent_card: AgentCard, context_token: ContextToken) -> AsyncIterator[Client]:
+async def a2a_client(
+    agent_card: AgentCard,
+    context_token: ContextToken,
+) -> AsyncIterator[Client]:
     try:
         async with httpx.AsyncClient(
             headers={"Authorization": f"Bearer {context_token.token.get_secret_value()}"},
             follow_redirects=True,
             timeout=timedelta(hours=1).total_seconds(),
         ) as httpx_client:
             yield ClientFactory(ClientConfig(httpx_client=httpx_client, use_client_preference=True)).create(
-                card=agent_card
+                card=agent_card,
             )
     except A2AClientError as ex:
         card_data = json.dumps(