[Feat]: Complete A2A Push Notification Protocol Support in PushNotificationSender

[tomboe311]

Is your feature request related to a problem? Please describe.

The current implementation of the Push Notification Sender and the Default Push Notification Sender only supports the task payload type.
According to the A2A protocol specification, multiple additional payload types such as artifactUpdate, message, and statusUpdate are allowed. These payloads are not supported in the SDK, which leads to incomplete protocol compliance and prevents integrators from using the full set of push notification features defined by the A2A standard.

Describe the solution you'd like

I would like the SDK to fully implement the A2A Push Notification Protocol by supporting all payload types defined in the specification. This includes:

• Extending the payload type definitions beyond task
• Implementing support for artifactUpdate, message, statusUpdate, and any other protocol-defined payloads
• Ensuring proper validation of payload structure and required fields
• Updating PushNotificationSender and DefaultPushNotificationSender to handle these payload types consistently

This will ensure full protocol compliance and enable developers to use the complete notification feature set.

Describe alternatives you've considered

Implementing only the payload types needed for specific use cases, but this would again result in partial protocol support and lead to inconsistencies in the future.
Creating custom sender implementations outside the SDK, but this fragments the ecosystem and duplicates effort.

Additional context

No response

Code of Conduct

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[ishymko]

Hi @tomboe311, thanks for reporting the issue! This is going to be done definitely.

Worth mentioning though, that the spec you've linked here is not yet released, as you may see page title says DRAFT v1.0. The latest released one v0.3 does not specify payloads the same way and gives an example of sending tasks as a payload, as done in the current implementation as well as in other SDKs.