feat(a2a): add rig-a2a client crate for consuming A2A agents as tools - #2204
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feat(a2a): add rig-a2a client crate for consuming A2A agents as tools#2204mccormickt wants to merge 3 commits into
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`HookContext` reported the run id, turn, streaming surface and agent name, but not which conversation the run continued. Only the runner knew that, and it used the id solely to load and append `ConversationMemory`. A hook is where per-conversation state belongs. A provider that keeps its own session on the far side of the wire — an A2A `contextId`, a hosted assistant thread — needs to know which conversation a run continues in order to attach its own identifiers, and no hook event carried that. Report it on `HookContext` alongside the rest of the run's identity. The id is what the caller named, independent of whether a memory backend consumed it: an explicit `chat_history` bypasses load and save while leaving the conversation named, and only `without_memory` clears it.
… hooks `CompletionResponse` and `StreamResponseFinish` carried the message id but not the response id, so the two response-scoped surfaces disagreed with the rest of Rig: `CompletionResponse::response_id` is populated by every provider and reported as `gen_ai.response.id`, yet no hook could read it. It is deliberately not promoted into history — `response_scoped_id_is_not_promoted_into_history` pins that — which leaves a hook as the only place a turn can be correlated with a provider's own logs, or with state a provider keeps per response. Report it on both events. The streaming side reads it from the terminal record, so a stream that ended early reports `None` rather than inventing one.
Consume remote Agent2Agent (A2A) protocol agents from Rig two ways: - A2AClient::tool projects a whole remote agent as one Rig tool taking a single prompt. A2A carries no skill selector, so a card's skills are documentation in the tool description, not separate tools. - A2AModel implements CompletionModel over message/send and message/stream, so A2AClient::agent backs a Rig Agent with a remote one. Request fields A2A cannot express — tools, output_schema, a demanding tool_choice — fail loudly rather than being dropped. Threading is host-side: ConversationId keys a bounded store of the server-issued contextId and taskId, so a model can neither forge an identifier nor lose one; task ids are reused only for tasks paused in input-required. Each call publishes an A2AThreadInfo for hooks. Remote states the caller cannot act on become typed tool errors carrying the remote's status text. A2AClient discovers the well-known AgentCard with a 1 MiB limit, selects the first supported JSON-RPC or HTTP+JSON interface in card order, validates it against the card origin, and forwards its optional tenant. Loopback tests cover both HTTP transports against the upstream a2a-server crate, a dev-dependency; the a2a_tool and a2a_agent examples demo each surface against the same stub, with no credentials. The integration is native-only because the upstream A2A networking stack does not support wasm32-unknown-unknown.
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An initial implementation of an integration with the Agent2Agent (A2A) protocol that allows consuming A2A agents as Rig tools:
The integration is native-only because the upstream A2A networking stack does not support wasm32-unknown-unknown.
Updates #391