Add Railiance WP-0025 custody adapter

Implement src/whitehat_security/platform_custody.py and focused tests
against the four custody schemas. Live admission still fails closed
without a value-safe projection receipt. No new engagement or traffic.

Assistant: grok
Assistant-Session: 01a02670-3345-76f2-a014-70fde8e2a2bb

workplans/WHITEHAT-WP-0003-platform-custody-adapter.md

@@ -0,0 +1,38 @@
+---
+id: WHITEHAT-WP-0003
+type: workplan
+title: "Consume the Railiance WP-0025 custody broker interface"
+domain: infotech
+repo: whitehat-security
+status: finished
+owner: net-kingdom
+topic_slug: whitehat-security
+created: "2026-08-22"
+updated: "2026-08-22"
+---
+
+# WHITEHAT-WP-0003 — platform custody adapter
+
+## Goal
+
+Implement the consumer Railiance asked for after `-02` aborted: a value-safe
+adapter at `src/whitehat_security/platform_custody.py` that understands the
+four WP-0025 custody schemas and can issue a plane lease from a projection
+receipt without seeing token values.
+
+This plan authorizes no engagement, runner, credential, or traffic.
+
+## Tasks
+
+### T01 — Schema-bound adapter and focused tests
+
+```task
+id: WHITEHAT-WP-0003-T01
+status: done
+priority: high
+```
+
+Adapter plus `tests/test_platform_custody_adapter.py`. Cleanup receipts can
+acknowledge a lease. Secret material is refused. `admit-plane --receipt`
+selects this adapter when the document uses
+`railiance.custody-projection-receipt`.