ReqManagedAgents.Provider for the Bedrock AgentCore backend — :request_response mode.
Each turn is one InvokeHarness call; resume re-sends the assistant toolUse + user
toolResult delta (the harness does not persist the uncommitted tool-use turn). Composes
the existing AgentCore.{Client, Converse} modules. Decoded events are additionally
delivered live to the session as {:provider_event, ev} messages while a turn streams.
The provision spec may carry opaque environment/environment_variables maps that pass
through to CreateHarness verbatim (filesystem mounts, custom containers, env vars — never
interpreted by this library).