ReqManagedAgents.Provider for the Anthropic Managed Agents backend — :streaming mode. A long-lived SSE stream pushes events; the client POSTs events to drive it; a turn ends on session.status_idle. Resume POSTs a user.custom_tool_result event (no echo — the session already holds the tool call). Composes Client, Stream, Event.

normalize/1 keys off the most recent status event. events, text, and server_tool_uses reflect exactly the events passed in (a partial list yields a partial view).

A model_config: %{api_key:, base_url:} opt builds the client when no :client is injected — the canonical way to run a session on a granted key + routed base_url.