Turn-owned runtime wrapper threaded across the tool-call suspend/resume boundary.
It embeds an AgentEngine.Session (read its :session field) and
carries the working AgentEngine.Transcript so a suspended turn can resume.
It is returned in the third position of turn/3's success tuple, keeping
the frozen {:ok, content, runtime, signals} shape while avoiding any
extension of AgentEngine.Session's public fields.
Summary
Types
@type t() :: %AgentEngine.Turn.Runtime{ session: AgentEngine.Session.t(), transcript: AgentEngine.Transcript.t() }