Opt-in context windows within a stable logical session. Rollover seals
eligible source evidence before changing the next request; never calls an LLM
summarizer or clears environment state. A durable successor starts fresh
elapsed time; cumulative resource/cost budgets remain unchanged.
Bundle of all dependencies needed to drive a streaming agent loop.
Constructed once by Runtime::run_stream_with_messages before spawning the stream task.
Host activation policy for MODEL-INITIATED activate_tools
(tools.activation_confirm + server.auto_approve_confirms).
Emit an after_tool_call event and return the tool output to record in
history — either the original output, or a Replace { output }
substituted by an extension transform hook (compression, redaction,
summarization). The runtime tool name is included when it differs from the
API-safe name.
Emit a before_tool_call event and include the runtime tool name when it
differs from the API-safe name. session_id is the owning conversation
(None for workers → JSON null, unchanged).