[Bug]: Agent Card not retrieved if all interfaces supports only protocol version 1.0

[carmine-sacco]

What happened?

It looks that at least one interface must support protocol version 0.3 when you use create_agent_card_routes from a2a.server.routes.agent_card_routes. The issue is because the function to_compat_agent_card convert the agent card to format into 0.3 version and it doesn't provide any interface if there isn't anyone with legacy version 0.3.

def to_compat_agent_card(core_card: pb2_v10.AgentCard) -> types_v03.AgentCard:
    # Map supported interfaces back to legacy layout
    """Convert agent card to v0.3 compat type."""
    compat_interfaces = [
        interface
        for interface in core_card.supported_interfaces
        if (
            (not interface.protocol_version)
            or is_legacy_version(interface.protocol_version)
        )
    ]
    if not compat_interfaces:
        raise errors.VersionNotSupportedError(
            'AgentCard must have at least one interface with compatible protocol version.'
        )

Is it a BUG or is it an architecture decision?

Relevant log output

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[rohityan]

Hi @carmine-sacco , If you are building a v1.0-only agent, you do not need to support version 0.3 . The VersionNotSupportedError is expected and handled gracefully, allowing the server to serve the correct modern card metadata to modern clients. It is an architecture decision.

[carmine-sacco]

Yes I saw the management of VersionNotSupportedError. By the way, actually the best approach is to support the v0.3 too since I expect that there aren't many agents supporting the version 1.0. A2A Inspector doesn't support the v1.0.