RemoteA2AAgent fails to send taskId in multi-turn scenarios

[kthota-g]

🔴 Required Information

Describe the Bug:
RemoteA2AAgent only sends contextId and doesn't send the associated taskId for multi-turn A2A scenarios.

Steps to Reproduce:

1. Create an agent with a RemoteA2AAgent as show below. You can use currency agent from a2a-samples repository.

from google.adk.agents.llm_agent import Agent

from google.adk.agents.remote_a2a_agent import RemoteA2aAgent

currency_agent = RemoteA2aAgent(
    name="currency_agent",
    agent_card="http://localhost:10999/.well-known/agent-card.json",
)

root_agent = Agent(
    model='gemini-2.5-flash',
    name='root_agent',
    description='A helpful assistant for user questions.',
    instruction='Helpful assistant to answer user queries. Use currency_agent for any currency related queries from the user',
    sub_agents=[currency_agent]
)

2. Launch adk web and start a new conversation with message 'How much is 10 USD?'.
3. A2A agent responds back with message 'Provide the currency to convert to' and task.status='input-required'.
4. Send the message 'CAD' as user's second turn.

Expected Behavior:
ADK should invoke the remote agent with task_id and context_id for the second turn as the task has not terminated.

Observed Behavior:
ADK only sends the context_id in the ADK payload. This results in unexpected agent behavior and results in creation of new tasks for every turn and stale task records get created.

---

🟡 Optional Information

adk-python/src/google/adk/agents/remote_a2a_agent.py

Line 643 in 4b677e7

a2a_request = A2AMessage(

only sets the context_id.

Ideally RemoteA2AAgent implementation should include the taskId when the task status is in paused awaiting user input such as 'input-required', 'auth-required' states.

Regression:
No

How often has this issue occurred?:

• Always (100%)