The one canonical recipe for wiring a routed placement into an agent session: granted key + routed base_url into model_config, budget guard from the grant, correlation metadata for decision-linked ingestion. Produces a plain keyword list targeting RMA's documented session options — no RMA types imported.

{:ok, resp} = Mimir.RouterClient.route(descriptor, client_opts)
session_opts = Mimir.Sessions.opts(resp, base_url: gateway_url)
Session.run(provider, session_opts ++ [handler: MyTools, prompt: prompt])

resp is already a %Mimir.RouteResponse{} (built by Mimir.RouteResponse.new/1 at the parse boundary).

opts/2 raises ArgumentError on a no-candidate or malformed route response — fail at composition time, not mid-session. Mimir.Guard handles the mid-run side and never raises.

The api_key/base_url pair is the data-plane half (hard enforcement at the gateway's budget constraint) for lanes that traverse a gateway; turn_guard is the control-plane half for runtimes the gateway cannot front. Both ride along on every placement; each runtime uses what applies.