AgentCapabilities
data class AgentCapabilities(val v1: AgentCapabilitiesV1, val otherVersions: Map<String, JsonElement> = emptyMap())
What an agent can generate, advertised to renderers.
The object is keyed by protocol version so one agent card can advertise several at once. This library reads the A2ui.PROTOCOL_VERSION entry into v1 and carries the rest through in otherVersions — refusing a card for also advertising v0.9 would refuse most real agents.