docs: ADR-0027 + demo note — public-safe RegisterRecord objecttype schema (refs #141)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/demo-script.md

@@ -5,6 +5,35 @@ copy-pasteable walkthrough against a local `make up` stack.
 
 ---
 
+## S-18c — RegisterRecord objecttype defined + registered (#141, ADR-0027)
+
+**Outcome:** a **RegisterRecord** objecttype with a **published** JSON schema is registered in the
+Objecttypen API at startup. The schema is public-safe by construction — `id`, `status`, `reference`
+only, mirroring the BFF's `OpenbaarEntry` (no `bsn`/`naam`), `dataClassification: open`. This is the
+schema S-19 writes register records against on approval. A `registerrecord-init` one-shot creates it
+over the API once Objecttypen is healthy (the Objecttypen `setup_configuration` has no objecttype
+step), idempotently.
+
+```bash
+make up
+# The RegisterRecord objecttype exists with a published version:
+curl -s -H "Authorization: Token 0123456789abcdef0123456789abcdef01234567" \
+  "http://localhost:8020/api/v2/objecttypes" | python3 -c \
+  'import sys,json; o=[x for x in json.load(sys.stdin)["results"] if x["name"]=="RegisterRecord"][0]; print(o["name"], o["dataClassification"], o["versions"])'
+#   → RegisterRecord open ['http://.../objecttypes/<uuid>/versions/1']
+#
+# Automated (a CI verify-stack step): asserts the objecttype exists, has a published version, and
+# that version's schema carries id/status/reference.
+make verify-registerrecord     # → OK — RegisterRecord v1 published, fields=['id', 'reference', 'status']
+```
+
+**The path:** `infra/objecttypen-registerrecord/registerrecord.schema.json` (the reviewed public-safe
+contract) + `register.py` are streamed into an external config volume by `infra/seed-config.sh
+registerrecord` (bind-mounted locally); the `registerrecord-init` one-shot POSTs the objecttype + a
+published version. Re-running is a no-op. S-19 (#20) writes records against this schema in Objecten.
+
+---
+
 ## S-18b — Objecten API up in compose, wired to Objecttypen (#140)
 
 **Outcome:** the upstream Maykin **Objecten API** runs in the stack — own **PostGIS** DB + redis,