Research: presence provider library/launcher split prior art (cultlib-gaps B4b2)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

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

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+# 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.