docs: consolidate agent execution and custody

engagements/pilots/eng-coulomb-railiance01-ho-001/vault/handoff/README.md

@@ -1,6 +1,7 @@
 # Handoff pack — eng-coulomb-railiance01-ho-001
 
-Filled during **ramp-down** (RD-02).
+Prepared during **ramp-down** (RD-02). The custody target was selected on
+2026-08-20, but the receiving repository has not yet accepted the transfer.
 
 ## Contents (when complete)
 
@@ -10,4 +11,18 @@ Filled during **ramp-down** (RD-02).
 - Deferred patches and reboot debt
 - Contacts and access revocation status
 
-_Status: not started (engagement not in ramp_down)._
+## Custody
+
+- Owner: `coulomb`
+- Classification: `client_confidential`
+- Current location: transitional supplier custody in `kaizen-agentic`
+- Receiving authority: `railiance-infra`
+- Proposed path:
+  `docs/evidence/resource-hosteurope-railiance01/engagements/eng-coulomb-railiance01-ho-001/`
+- Transfer record: `custody-transfer.yaml`
+
+The complete engagement tree, rather than only this handoff directory, must be
+transferred because metrics, reports, approvals, and commercial metadata are
+all client records. The source is retained until explicit receiver acceptance.
+
+_Status: handoff target selected; transfer proposed; engagement still operating._