Add a new `A2A` call task

[cdavernas]

What would you like to be added?

Add a new call task for the Agent-to-Agent Protocol (A2A), enabling secure and structured communication between agentic systems within workflows. This task would make it possible to invoke A2A-compliant endpoints and pass structured messages following the A2A specification.

The task should support:

• Discovering agents using the A2A discovery endpoint
• Sending A2ARequest messages to a remote agent or service,
• Receiving and handling the corresponding A2AResponse,
• Optional streaming for multi-part or progressive responses,
• Support for headers, metadata, and error codes defined by A2A.

This addition would enable interoperable, agent-native operations within declarative workflows and facilitate integration with a growing ecosystem of A2A-aware systems.

Proposal(s):

Introduce a new task type, e.g. a2a, to handle outbound A2A messages. This task would be modeled around the A2A JSON-based protocol and support the following configuration:

• A server field specifying the target A2A server,
• A method field containing the name of the A2A request to perform
• A parameters field containing the request's parameters
• An optional protocol (version) to allow future-proofing.

On execution, the workflow runtime should:

• Format and send the message according to the A2A protocol over HTTP(S) (JSON RPC),
• Await and parse the A2AResponse,
• Handle errors (e.g., error.code, error.message) per A2A spec,
• Optionally process streaming responses if supported by the agent.

This proposal enables workflows to natively speak A2A, paving the way for standardized, composable agent orchestration across services.

Alternative(s):

No response

Additional info:

No response

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