Telemetry session ownership

Problem

The CLI initializes telemetry once per process. That process-global session is safe for an interactive CLI, but a daemon can host multiple sessions. Native LLM spans created outside an interaction currently fall back to the bootstrap session, even though LoggingContentGenerator owns the Config for the session that issued the request. API log spans use that Config, so one model request can be split across two sessions.

Ownership

An existing native logical parent owns its descendants. Without one, the Config owned by LoggingContentGenerator is authoritative. The resolved session is carried in an OpenTelemetry Context so automatic HTTP spans and log records created during the request inherit the same identity.

Session resolution uses this order:

1. Native interaction, subagent, or tool parent.
2. Explicit session from the owning Config.
3. Session stored in the active OpenTelemetry Context.
4. The existing per-request session AsyncLocalStorage.
5. The process-global session, for single-session compatibility.

The OpenTelemetry context key is private and is not baggage, so it is not serialized onto outbound requests. A streaming request snapshots its resolved session when the LLM span starts, uses the same snapshot for API log records, and reactivates that context for every stream iteration. A later Config session change therefore cannot split an in-flight request across sessions.

Boundaries

This change fixes session ownership only. It does not add AgentLoop entry or step spans, turn or react-round attributes, resource-level session identity, or any wire, storage, or daemon API changes.