Finish reef-railiance first-wave handoff

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