diff --git a/docs/architecture/adr-0028-objecten-holds-the-register.md b/docs/architecture/adr-0028-objecten-holds-the-register.md
index 14c7bd4..b521cc8 100644
--- a/docs/architecture/adr-0028-objecten-holds-the-register.md
+++ b/docs/architecture/adr-0028-objecten-holds-the-register.md
@@ -77,6 +77,38 @@ is not cached, so it is retried on the next approval.
 - Upgrade path: lift it into a singleton cache (as `CachedZaaktypeCatalog` does for ZGW)
   if approvals ever get hot enough for that GET to matter.
 
+### The objecttype's UUID is pinned, not server-assigned
+
+Objecten refuses to store an object whose objecttype it has not been configured with
+(`ObjectType with url=… is not configured`), and its configuration identifies an
+objecttype **by UUID** — supplied through a static `setup_configuration` file applied
+when the container starts, before the `registerrecord-init` one-shot has run.
+
+Rather than thread a seed-time UUID from one container into another's config, the UUID is
+**pinned**: `infra/objecttypen-registerrecord/register.py` creates the objecttype with a
+fixed UUID (the Objecttypen API accepts a client-supplied one), and
+`infra/objecten/setup_configuration/data.yaml` declares that same UUID. Both sides are
+declared up front, both stay idempotent, and neither has to wait for the other.
+
+The cost is a constant duplicated across two files that must be kept in step; each carries
+a comment pointing at the other.
+
+### Objecten's notifications are off for this slice
+
+Objecten publishes to a Notificaties API on every write, and `notifications_api_common`
+**raises** rather than skipping when that configuration is absent — so with no NRC wiring,
+every `POST /api/v2/objects` returns 500 after creating and rolling back the object.
+
+Objecten → NRC is not wired: there is no broker, no Celery worker, no `objecten` kanaal and
+no abonnement for it. Configuring only the client side would make writes succeed while
+every message was dropped on the floor — a delivery path that looks wired and isn't. So
+`NOTIFICATIONS_DISABLED` is set for Objecten in both compose files instead.
+
+- ponytail ceiling: Objecten emits no notifications, so nothing downstream can react to a
+  register write yet.
+- Upgrade path: S-19b (#150) needs those notifications to source the projection from
+  Objecten, and turns them on together with the broker, worker, kanaal and abonnement.
+
 ## Consequences
 
 **Positive**
@@ -95,6 +127,8 @@ is not cached, so it is retried on the next approval.
   Nothing repairs that automatically yet.
 - One more upstream module on the approval path, and one more dev credential
   (`Acl__Objecten__Token`) in compose.
+- Two new hand-kept constants: the pinned objecttype UUID (two files) and the objecttype
+  name (compose + `register.py`).
 - Until S-19b lands, the public register is still read from the NRC-derived projection, so
   the register record is written but not yet read — the two must agree.
 
@@ -110,3 +144,8 @@ and no service reaches Objecten's database.
 asserts, via `infra/register-record-check.py`, that Objecten holds exactly one
 `RegisterRecord` for that registration, with status `INGESCHREVEN` and no field outside
 the public-safe schema.
+
+Every HTTP exchange the gateway performs was additionally replayed by hand against a live
+Objecten + Objecttypen pair while writing this slice — objecttype lookup by name, version
+status, `data_attrs` search, create, update, and a rejected write carrying a `bsn`. Both
+findings above came out of that replay rather than out of CI.
diff --git a/infra/docker-compose.local.yml b/infra/docker-compose.local.yml
index 9660876..e35732b 100644
--- a/infra/docker-compose.local.yml
+++ b/infra/docker-compose.local.yml
@@ -691,6 +691,12 @@ services:
       CACHE_AXES: objecten-redis:6379/0
       DISABLE_2FA: "true"
       OTEL_SDK_DISABLED: "true"
+      # S-19a: Objecten refuses every write while its Notificaties config is absent
+      # (notifications_api_common raises rather than skipping, so POST /objects 500s). Objecten →
+      # NRC is not wired yet — there is no broker, worker, kanaal or abonnement for it — so turn
+      # notifications off rather than fake a delivery path that silently drops every message.
+      # S-19b (#150) sources the projection from Objecten and turns this back on for real.
+      NOTIFICATIONS_DISABLED: "true"
       RUN_SETUP_CONFIG: "true"
     command: /setup_configuration.sh
     volumes:
diff --git a/infra/docker-compose.yml b/infra/docker-compose.yml
index 903cd3f..024e879 100644
--- a/infra/docker-compose.yml
+++ b/infra/docker-compose.yml
@@ -717,6 +717,12 @@ services:
       CACHE_AXES: objecten-redis:6379/0
       DISABLE_2FA: "true"
       OTEL_SDK_DISABLED: "true"
+      # S-19a: Objecten refuses every write while its Notificaties config is absent
+      # (notifications_api_common raises rather than skipping, so POST /objects 500s). Objecten →
+      # NRC is not wired yet — there is no broker, worker, kanaal or abonnement for it — so turn
+      # notifications off rather than fake a delivery path that silently drops every message.
+      # S-19b (#150) sources the projection from Objecten and turns this back on for real.
+      NOTIFICATIONS_DISABLED: "true"
       RUN_SETUP_CONFIG: "true"
     command: /setup_configuration.sh
     # data.yaml is streamed into this external volume by infra/seed-config.sh before start.
diff --git a/infra/objecten/setup_configuration/data.yaml b/infra/objecten/setup_configuration/data.yaml
index 1a5b2a3..9f1b858 100644
--- a/infra/objecten/setup_configuration/data.yaml
+++ b/infra/objecten/setup_configuration/data.yaml
@@ -19,7 +19,18 @@ zgw_consumers:
       header_key: Authorization
       header_value: Token 0123456789abcdef0123456789abcdef01234567
 
-# (2) Static API token peers use to write/read objects.
+# (2) Permit the RegisterRecord objecttype (S-19a). Objecten refuses to store an object whose
+# objecttype it has not been configured with ("ObjectType with url=… is not configured"), and it
+# identifies one by uuid — which is why infra/objecttypen-registerrecord/register.py pins that uuid
+# instead of letting Objecttypen assign one. Keep the two in step.
+objecttypes_config_enable: true
+objecttypes:
+  items:
+    - uuid: 1f4b4e26-8b1f-4e2f-9d6c-6a1b7a2f0e01
+      name: RegisterRecord
+      service_identifier: objecttypen
+
+# (3) Static API token peers use to write/read objects.
 tokenauth_config_enable: true
 tokenauth:
   items:
diff --git a/infra/objecttypen-registerrecord/register.py b/infra/objecttypen-registerrecord/register.py
index df07aad..fa6e69f 100644
--- a/infra/objecttypen-registerrecord/register.py
+++ b/infra/objecttypen-registerrecord/register.py
@@ -17,6 +17,11 @@ BASE = os.environ.get("OBJECTTYPEN", "http://objecttypen:8000").rstrip("/")
 TOKEN = os.environ["OBJECTTYPEN_TOKEN"]
 SCHEMA_PATH = os.environ.get("SCHEMA", "/config/registerrecord.schema.json")
 NAME = "RegisterRecord"
+# Pinned rather than server-assigned (S-19a): the Objecten API will only accept objects whose
+# objecttype it has been configured with *by uuid*, and its own setup_configuration is a static
+# file applied before this one-shot runs. A fixed uuid lets both sides be declared up front instead
+# of threading a seed-time value between two containers. See infra/objecten/setup_configuration.
+UUID = "1f4b4e26-8b1f-4e2f-9d6c-6a1b7a2f0e01"
 
 
 def api(method, path, body=None):
@@ -53,6 +58,7 @@ def main():
         return 0
 
     ot = existing or api("POST", "/api/v2/objecttypes", {
+        "uuid": UUID,
         "name": NAME,
         "namePlural": "RegisterRecords",
         "description": schema.get("description", ""),