feat: add a TextClient class for a simplified text-based communication

[sokoliva]

Description

This feature dramatically reduces the complexity for common text-only exchanges, improving developer experience.

Changes

• Add TextClient, a facade around Client that simplifies text-based
  communication by hiding proto construction, stream iteration, and
  multi-part text aggregation behind a single send_text_message method.
• Add create_text_client factory function mirroring create_client,
  and export both from a2a.client.
• Add samples/text_client_cli.py as a minimal worked example, and
  samples/README.md documenting all three sample files.
• Refactor samples/cli.py to iterate StreamResponse directly and
  use the shared get_message_text helper.

Tested

Output from running simpletext_client_cli.py

uv run samples/text_client_cli.py 
Connecting to http://127.0.0.1:41241 (preferred transport: Any)

✓ Agent Card Found:
  Name: Sample Agent
  Picked Transport: JsonRpcTransport

Connected! Send a message or type /quit to exit.
You: hi
Agent: Processing your question... Hello World! Nice to meet you!
You: bye
Agent: Processing your question... Goodbye! Have a wonderful day!
You: /quit

Output from running non-simplified cli.py

uv run samples/cli.py
Connecting to http://127.0.0.1:41241 (preferred transport: Any)

✓ Agent Card Found:
  Name: Sample Agent
  Picked Transport: JsonRpcTransport

Connected! Send a message or type /quit to exit.
You: hi
Task [state=TASK_STATE_SUBMITTED]
TaskStatusUpdate [state=TASK_STATE_WORKING]: Processing your question...
TaskArtifactUpdate [name=response]: Hello World! Nice to meet you!
TaskStatusUpdate [state=TASK_STATE_COMPLETED]: 
--- Task Completed ---
You: bye
Task [state=TASK_STATE_SUBMITTED]
TaskStatusUpdate [state=TASK_STATE_WORKING]: Processing your question...
TaskArtifactUpdate [name=response]: Goodbye! Have a wonderful day!
TaskStatusUpdate [state=TASK_STATE_COMPLETED]: 
--- Task Completed ---
You: /quit

Fixes #959 🦕

[github-actions]

🧪 Code Coverage (vs 1.0-dev)

⬇️ Download Full Report

	Base	PR	Delta
src/a2a/client/client_factory.py	88.67%	88.89%	🟢 +0.22%
src/a2a/client/text_client.py (new)	—	84.62%	—
Total	92.53%	92.48%	🔴 -0.05%

Generated by coverage-comment.yml

[gemini-code-assist]

Code Review

This pull request introduces TextClient, a facade that simplifies text-based communication by aggregating response parts into a single string, and refactors the existing CLI sample to use message utilities. It includes a new sample CLI, factory methods, and unit tests. Feedback suggests improving lifecycle management via the asynchronous context manager protocol, refining response aggregation to handle streamed tokens correctly, and utilizing existing utilities to reduce code duplication in the new client.

[msampathkumar]

agent word is too broad. Can we do ?

Suggested change

	agent: str | AgentCard,
	agent_card: str | AgentCard,

[sokoliva]

agent can also be the base URL of the agent so renaming it to agent_card could be misleading. WDYT?

[msampathkumar]

Hi, when I do

text_client = await create_text_client(
    agent=SERVER_URL,
    client_config=ClientConfig(streaming=False, supported_protocol_bindings="JSONRPC")
)

I get

Traceback (most recent call last):
 ....
 ....
 ....
  File ".../a2a/client/client_factory.py", line 360, in create
    return BaseClient(
        card,
    ...<2 lines>...
        interceptors or [],
    )
TypeError: 
TypeError: BaseClient.__init__() missing 1 required positional argument: 'interceptors'