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

The A2A spec and reference implementations primarily recommend SSE for HTTP transports.

But, SSE doesn't cooperate well with existing gateways, tracing system. Also rich types/message could overload text/event-stream lines.

In contrast, Streamable HTTP which leverages "HTTP chunked transfer" is more convenient for such purpose:

• Structured frames without overloading text/event-stream lines.
• Native binary support avoiding base64 inflation, also supports large payload.
• Long-time support confirmed with existing gateways/middleboxes.

Consider adding an optional “StreamHTTP” transport might be a good choice.

Describe the solution you'd like

In MCP spec&refs, Streamable HTTP has already been the default and recommended transport since protocol version 2024-11-05.

There are similarities between A2A and MCP protocols, so it can be a good reference implementation.

Describe alternatives you've considered

No response

Additional context

If HTTP+SSE and StreamableHTTP both serve on the same http path, a "transport negotiation" might needed.

Ref: https://modelcontextprotocol.io/specification/2025-06-18/basic/transports#backwards-compatibility

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