Failing task cancellation tests (Task cannot be canceled - current state: Completed)

## 📝 Description

I have six agents that fully comply with the **official A2A Inspector** specifications and correctly implement all required A2A methods — namely `tasks/get` and `tasks/cancel`.

However, when running the **TCK** against these agents, I consistently encounter errors related to **cancellation of already completed tasks**.

I’ve already tried introducing artificial delays in the agent’s responses to prevent tasks from completing instantly, but this didn’t resolve the issue.

Could this behavior be related to **version compatibility** — for instance, between the **A2A SDK v0.3.8** and the TCK tests built for **v0.3.0**?
Does the TCK currently support all **v0.3.x** agents, or is it limited to **v0.3.0**?

Any suggestions on why this might be happening and/or how to overcome these failures to ensure that my agents pass all the mandatory tests?

---

## ⚙️ Version Information

* **A2A SDK:** `v0.3.8`

## 🐛 Errors

```
======================================================= FAILURES =======================================================
___________________________ TestMethodMappingCompliance.test_core_method_mapping_compliance ____________________________
tests/mandatory/protocol/test_a2a_v030_new_methods.py:384: in test_core_method_mapping_compliance
assert cancelled_task["id"] == task_id
^^^^^^^^^^^^^^^^^^^^
E KeyError: 'id'

During handling of the above exception, another exception occurred:
tests/mandatory/protocol/test_a2a_v030_new_methods.py:387: in test_core_method_mapping_compliance
pytest.fail(f"Core method mapping test failed on {transport_type}: {e}")
E Failed: Core method mapping test failed on jsonrpc: 'id'
------------------------------------------------- Captured stdout call -------------------------------------------------
{'error': {'code': -32002, 'message': 'Task cannot be canceled - current state: TaskState.completed'}}
-------------------------------------------------- Captured log call ---------------------------------------------------
ERROR tck.transport.jsonrpc_client.JSONRPCClient:jsonrpc_client.py:143 JSON-RPC error from SUT: {'code': -32002, 'message': 'Task cannot be canceled - current state: TaskState.completed'}
___________________________________________ test_message_send_continue_task ____________________________________________
tests/mandatory/protocol/test_message_send_method.py:183: in test_message_send_continue_task
assert is_json_rpc_success_response(second_resp), f"Task continuation failed: {second_resp}"
E AssertionError: Task continuation failed: {'error': {'code': -32602, 'message': 'Task d51a9cf0-7576-4c65-9007-7766e366c337 is in terminal state: completed'}}
E assert False
E + where False = is_json_rpc_success_response({'error': {'code': -32602, 'message': 'Task d51a9cf0-7576-4c65-9007-7766e366c337 is in terminal state: completed'}})
-------------------------------------------------- Captured log call ---------------------------------------------------
ERROR tck.transport.jsonrpc_client.JSONRPCClient:jsonrpc_client.py:143 JSON-RPC error from SUT: {'code': -32602, 'message': 'Task d51a9cf0-7576-4c65-9007-7766e366c337 is in terminal state: completed'}
_______________________________________________ test_task_history_length _______________________________________________
tests/mandatory/protocol/test_state_transitions.py:80: in test_task_history_length
assert transport_helpers.is_json_rpc_success_response(update_resp)
E AssertionError: assert False
E + where False = ({'error': {'code': -32602, 'message': 'Task 62211576-c2e8-45fe-a170-36900bc0cfd2 is in terminal state: completed'}})
E + where = .is_json_rpc_success_response
-------------------------------------------------- Captured log call ---------------------------------------------------
ERROR tck.transport.jsonrpc_client.JSONRPCClient:jsonrpc_client.py:143 JSON-RPC error from SUT: {'code': -32602, 'message': 'Task 62211576-c2e8-45fe-a170-36900bc0cfd2 is in terminal state: completed'}
_______________________________________________ test_tasks_cancel_valid ________________________________________________
tests/mandatory/protocol/test_tasks_cancel_method.py:53: in test_tasks_cancel_valid
assert is_json_rpc_success_response(resp), f"Task cancellation failed: {resp}"
E AssertionError: Task cancellation failed: {'error': {'code': -32002, 'message': 'Task cannot be canceled - current state: TaskState.completed'}}
E assert False
E + where False = is_json_rpc_success_response({'error': {'code': -32002, 'message': 'Task cannot be canceled - current state: TaskState.completed'}})
-------------------------------------------------- Captured log call ---------------------------------------------------
ERROR tck.transport.jsonrpc_client.JSONRPCClient:jsonrpc_client.py:143 JSON-RPC error from SUT: {'code': -32002, 'message': 'Task cannot be canceled - current state: TaskState.completed'}
=============================================== short test summary info ================================================
FAILED tests/mandatory/protocol/test_a2a_v030_new_methods.py::TestMethodMappingCompliance::test_core_method_mapping_compliance - Failed: Core method mapping test failed on jsonrpc: 'id'
FAILED tests/mandatory/protocol/test_message_send_method.py::test_message_send_continue_task - AssertionError: Task continuation failed: {'error': {'code': -32602, 'message': 'Task d51a9cf0-7576-4c65-9007-7766e...
FAILED tests/mandatory/protocol/test_state_transitions.py::test_task_history_length - AssertionError: assert False
FAILED tests/mandatory/protocol/test_tasks_cancel_method.py::test_tasks_cancel_valid - AssertionError: Task cancellation failed: {'error': {'code': -32002, 'message': 'Task cannot be canceled - current ...
```