docs: A2A send/get task documentation

docs/a2a.md

@@ -94,3 +94,149 @@ uvicorn agent_to_a2a:app --host 0.0.0.0 --port 8000
 ```
 
 Since the goal of `to_a2a` is to be a convenience method, it accepts the same arguments as the [`FastA2A`][fasta2a.FastA2A] constructor.
+
+### Interacting with the A2A Server using a Client
+
+For client-server interaction, we can create a client using the [`A2AClient`][fasta2a.client.A2AClient] class, which enables us to send and get tasks from the agent. In FastA2A, we expose two methods `send_task` and `get_task` to do so.
+```python
+from fasta2a.client import A2AClient
+
+client = A2AClient(base_url='http://localhost:8000')
+```
+
+To send a task for execution, we create a [`Message`][fasta2a.schema.Message] object and pass it to the client's `send_task` function. (example from [Google](https://google.github.io/A2A/tutorials/python/6-interact-with-server/#understanding-the-client-code)):
+```python
+from fasta2a.client import A2AClient
+from fasta2a.schema import Message
+
+client = A2AClient(base_url='http://localhost:8000')
+
+async def send_message():
+    send_message_payload = Message(
+        role='user',
+        parts=[
+            {'type': 'text', 'text': 'How much is 10 USD in INR?'}
+        ]
+    )
+
+    response = await client.send_task(message=send_message_payload)
+    print(response)
+    """
+    {
+        'jsonrpc': '2.0',
+        'id': '09cd5ee1-81ca-4779-8679-47c002e5a09f',
+        'result': {
+            'id': 'b6e6cce0-bd98-43c7-8104-c5ce0836f2f6',
+            'session_id': 'c0642116-b579-427e-a5e1-4bb2b41244f8',
+            'status': {
+                'state': 'submitted',
+                'timestamp': '2025-05-14T12:33:50.618260'
+            },
+            'history': [
+                {'role': 'user', 'parts': [{'type': 'text', 'text': 'how much is 10 USD in INR?'}]}
+            ]
+        }
+    }
+    """
+```
+
+Ensure that you call the main method using `asyncio.run` to execute the asynchronous code.
+
+We can use the `get_task` function to get the status and result from the task, however we need the result ID from the response in order to do so. Note that the task may still be in-progress on the agent's side while this is taking place.
+```python {hl_lines="3 17-20"}
+from fasta2a.client import A2AClient
+
+client = A2AClient(base_url='http://localhost:8000')
+
+async def send_message(send_message_payload):
+    response = await client.send_task(message=send_message_payload)
+    response_task_id = str(response['result']['id'])
+    processed_task_response = await client.get_task(task_id=response_task_id)
+    print(processed_task_response)
+    """
+    {
+        'jsonrpc': '2.0',
+        'id': None,
+        'result': {
+            'id': '...',
+            'session_id': '...',
+            'status': {
+                'state': 'working',
+                'timestamp': '2025-05-14T19:36:45.963421'
+            },
+            'history': [
+                {'role': 'user', 'parts': [{'type': 'text', 'text': 'how much is 10 USD in INR?'}]}
+            ]
+        }
+    }
+    """
+```
+
+In the case that you are debugging A2A using a client, you may want to add in a delay to retrieve the fulfilled response that you want from the agent.
+```python {hl_lines="10"}
+import time
+
+from fasta2a.client import A2AClient
+
+client = A2AClient(base_url='http://localhost:8000')
+
+async def send_message(send_message_payload):
+    response = await client.send_task(message=send_message_payload)
+    response_task_id = str(response['result']['id'])
+    time.sleep(2) # Adding in a delay to ensure that we get a fulfilled response.
+    processed_task_response = await client.get_task(task_id=response_task_id)
+    print(processed_task_response)
+    """
+    {
+        'jsonrpc': '2.0',
+        'id': None,
+        'result': {
+            'id': '...',
+            'session_id': '...',
+            'status': {
+                'state': 'completed', 'timestamp': '2025-05-14T19:13:07.759377'
+            },
+            'history': [
+                {'role': 'user', 'parts': [{'type': 'text', 'text': 'how much is 10 USD in INR?'}]}
+            ],
+            'artifacts': [
+                {'name': 'result', 'parts': [{'type': 'text', 'text': 'As of October 26, 2023, at 11:10 AM PST, 10 USD is approximately **833.18 INR**.\n\nKeep in mind that exchange rates fluctuate constantly, so this is just an estimate. For the most accurate conversion, you should check a real-time currency converter like Google Finance, XE.com, or a similar service just before you need the information.\n'}], 'index': 0}
+            ]
+        }
+    }
+    """
+```
+
+Here's the full code:
+```python {title="a2a_client.py"}
+import time
+
+from fasta2a.client import A2AClient
+from fasta2a.schema import Message
+
+client = A2AClient(base_url='http://localhost:8000')
+
+async def send_message():
+    send_message_payload = Message(
+        role='user',
+        parts=[
+            {'type': 'text', 'text': 'How much is 10 USD in INR?'}
+        ]
+    )
+
+    task_response = await client.send_task(message=send_message_payload)
+    task_response_result_id = str(task_response['result']['id'])
+    time.sleep(2) # <- Just for task fulfillment.
+    fulfilled_task_response = await client.get_task(task_id=task_response_result_id)
+    print(fulfilled_task_response['result']['artifacts'])
+    """
+    [
+        {
+            'name': 'result',
+            'parts': [{'type': 'text', 'text': 'As of October 26, 2023, at 11:10 AM PST, 10 USD is approximately **833.18 INR**.\n\nKeep in mind that exchange rates fluctuate constantly, so this is just an estimate. For the most accurate conversion, you should check a real-time currency converter like Google Finance, XE.com, or a similar service just before you need the information.\n'}],
+            'index': 0
+        }
+    ]
+    """
+```
+_(This example is complete, it can be run "as is" — you'll need to add `asyncio.run(main())` to run `main`)_