Function obs 

pub fn obs(pc_id: &str) -> String

obs.<pc_id> — per-PC observability event stream (Issue #246). The agent publishes one crate::wire::ObsEvent per timeline event (sign-in / out, power on / off, sleep / resume, agent milestones, diagnostic bundle pointers). Distinct from events.started.* (in-flight script lifecycle) and host_perf.<pc_id> (numeric telemetry) — obs.* is the semantic-event stream the SPA Timeline page consumes.