fix(samples): emit Task(TASK_STATE_SUBMITTED) as first streaming event

[sokoliva]

Description

Updates the sample agent and CLI to correctly follow the A2A streaming event contract, where the first event in a stream must be a Task or a Message object in TASK_STATE_SUBMITTED state.

Changes

hello_world_agent.py
SampleAgentExecutor.execute() now enqueues a Task(TASK_STATE_SUBMITTED) object as its very first event, before any TaskUpdater calls. The initial user message is included in the Task's history field, since the consumer sets message_to_save = None upon receiving a Task event (expecting the task to carry the message itself).

cli.py
Updates _handle_stream to match the new event contract:
The first event is now expected to be a Message or a Task (not an (event, task) tuple), and its id is used to initialize current_task_id.

README.md
Adds a README.md for the samples.

Tested

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 Finished ---
You: /quit

Related issue #965 🦕

BEGIN_COMMIT_OVERRIDE
chore(samples): emit Task(TASK_STATE_SUBMITTED) as first streaming event (#970)
END_COMMIT_OVERRIDE

[gemini-code-assist]

Code Review

This pull request introduces a README for the SDK samples and updates the sample agent and CLI client to better handle task streaming. Specifically, the agent now enqueues an initial task submission event, and the CLI processes streaming updates by extracting the task ID from the first event. Review feedback suggests expanding the CLI's initial event handling to include Message objects and ensuring the task ID is reset for all terminal task states, such as failures or cancellations, to maintain correct session state.

[github-actions]

🧪 Code Coverage (vs 1.0-dev)

⬇️ Download Full Report

No coverage changes.

Generated by coverage-comment.yml