CultLib/docs/research/2026-10-29-presence-provider-library-split-prior-art.md

Prior art: presence provider as a library, launcher as a consumer

Served: cultlib-gaps:cut_spec:cut-cultnet-rs-presence-provider-a.r1 and the Defaulted rulings presence-provider-network-free-core, presence-credentials-both-idunn-drivers and presence-provider-consumers-adopt, applying the operator's gamecult-chat:ruling:presence-one-owner-library-launcher-consumer. Imagination pass, 2026-10-29, from recall of the cited manuals (not re-fetched).

• libsystemd sd_notify(3): a service links a small library and reports its own state (READY, STATUS, WATCHDOG); programs that cannot link it use systemd-notify(1) or a wrapper. Same split as cultnet-rs provider plus idunn-launch as the sidecar consumer.
• sd_listen_fds_with_names(3): checks LISTEN_PID against the process, sets close-on-exec on passed descriptors, finds them by name, and can unset the LISTEN_* environment. This set is the descriptor rule the provider adopts.
• systemd watchdog (WATCHDOG=1 within WatchdogSec): the model for the warming heartbeat.
• Consul: TTL checks updated by the service through the client API, versus script/HTTP checks the agent runs for services that cannot. In-process versus sidecar again.
• Kubernetes: kubelet-run probes observe from outside; readiness gates are reported by the app. Idunn's route challenge is the outside observer, the signed presence the app's own report.

Existing copies compared: CodexConnector src/idunn_health.rs (two descriptors, strict PID check), Idunn launcher (two descriptors, no PID check), cultnet-ts idunn-runtime-authority.ts (descriptors by name, systemd private PID case). The provider takes the strictest union.