Finish reef-railiance first-wave handoff

docs/README.md

@@ -3,3 +3,4 @@
 - `wave-1-contract.md` — current grouped home-reef contract and boundary summary
 - `source-backed-substrate-facts.md` — source-backed first-wave facts imported from S1
 - `source-import-plan.md` — source material and migration direction from existing repos
+- `retained-s1-handoff.md` — migration-window split between grouped reef ownership and retained S1 authority

docs/retained-s1-handoff.md

@@ -0,0 +1,58 @@
+# Retained S1 Handoff
+
+## Purpose
+
+Define the migration-window handoff between `reef-railiance` and
+`railiance-infra` while grouped reef localization is still in flight.
+
+Wave 1 makes `reef-railiance` the durable owner of the grouped Railiance
+home-reef identity, topology, hosted-rail statement, and future `rapp`
+bindings. `railiance-infra` remains the canonical S1 owner of raw inventory,
+provisioning, hardening, and source-backed host facts that have not yet been
+localized into the reef repo.
+
+## Canonical Reef Surface
+
+Use `reef-railiance` as the canonical home for:
+
+- `declarations/reef.yaml`
+- `substrate/identity.yaml`
+- `substrate/topology.yaml`
+- `bindings/rails.yaml`
+- `bindings/rapps.yaml`
+- repo-local grouped-boundary docs, questions, and future reef-local runbooks
+
+New grouped-reef behavior, membership interpretation, hosted-rail stance, and
+future `rapp` binding decisions should land here first.
+
+## Retained S1 Surface
+
+Still owned by `railiance-infra`:
+
+- `inventory/servers.yaml` as the raw server identity source
+- Terraform/cloud-init/Ansible provisioning and convergence logic
+- generic OS hardening and substrate verification
+- canonical S1 docs such as `docs/reef-first-wave-source-map.md`
+- source-backed host facts that are still broader than the grouped home-reef
+  boundary
+
+## Current Compatibility Path
+
+Current operators do not need a flag day:
+
+1. Continue using `railiance-infra` for server provisioning, inventory edits,
+   SSH/bootstrap mechanics, and raw host-fact maintenance.
+2. Use `reef-railiance` for grouped home-reef identity, topology, hosted-rail
+   stance, and reef-local `rapp` binding decisions.
+3. When a raw server fact changes, update `railiance-infra` first, then refresh
+   the reef-local projection only where that fact affects the grouped reef
+   boundary.
+4. Keep unresolved grouped-membership or split criteria explicit in this repo
+   rather than forcing one permanent repo per server.
+
+## Exit Condition
+
+The migration window can end once the reef-specific interpretation no longer
+depends on broader S1 docs for routine operator understanding, and the
+remaining source-backed member facts needed by the grouped reef have been
+localized cleanly.

docs/source-import-plan.md

@@ -34,6 +34,19 @@ Do not import these into `reef-railiance` as part of wave 1:
 - generic Kubernetes runtime behavior
 - workload packaging or platform governance
 
+## Current Migration-Window Compatibility
+
+During wave 1:
+
+- `reef-railiance` is the canonical home for grouped home-reef identity,
+  topology, hosted-rail stance, and future `rapp` bindings
+- `railiance-infra` remains the canonical owner of raw inventory, provisioning,
+  and broader S1 source-backed host facts
+- raw host-fact changes should be made in `railiance-infra` first and then
+  projected here when they affect the grouped reef boundary
+
+See `docs/retained-s1-handoff.md` for the active handoff contract.
+
 ## Rule
 
 Imports into this repo should preserve the grouped home-reef boundary already

docs/wave-1-contract.md

@@ -52,6 +52,9 @@ Wave 1 `reef-railiance` must not assume:
 Until the extraction is complete, `railiance-infra` remains the canonical S1
 source of truth.
 
+The active migration-window compatibility rules live in
+`docs/retained-s1-handoff.md`.
+
 `reef-railiance` should become the durable grouped substrate home first. Only
 then should additional bindings, runbooks, and substrate-local overlays move
 here in a migration-safe sequence.