Merge pull request 'feat(event-subscriber): NRC event subscriber + rebuildable read projection (closes #7)' (#59) from feat/7-event-subscriber-projection into main

Reviewed-on: #59

.config/dotnet-tools.json

@@ -8,6 +8,13 @@
         "dotnet-stryker"
       ],
       "rollForward": false
+    },
+    "dotnet-ef": {
+      "version": "10.0.0",
+      "commands": [
+        "dotnet-ef"
+      ],
+      "rollForward": false
     }
   }
 }

.gitea/workflows/ci.yaml

@@ -62,6 +62,12 @@ jobs:
           name: acl-mutation-report
           path: services/acl/StrykerOutput/**/reports/mutation-report.html
           if-no-files-found: warn
+      - uses: https://github.com/actions/upload-artifact@v3
+        if: always()
+        with:
+          name: event-subscriber-mutation-report
+          path: services/event-subscriber/StrykerOutput/**/reports/mutation-report.html
+          if-no-files-found: warn
 
   # One stage for every check that needs the live stack. On the single self-hosted
   # runner jobs run sequentially, so booting OpenZaak once (instead of once per job)
@@ -80,10 +86,12 @@ jobs:
         run: make verify-acl
       - name: OpenZaak → NRC notification delivery
         run: make verify-nrc
+      - name: OpenZaak → NRC → Event Subscriber → projection-api
+        run: make verify-projection
       # Log dump must precede teardown (which removes the containers).
       - name: Dump container logs on failure
         if: failure()
-        run: docker compose -f infra/docker-compose.yml logs --no-color --tail=100 oz-init openzaak nrc-init nrc-web nrc-celery nrc-beat flowable-init keycloak acl bff 2>&1 || true
+        run: docker compose -f infra/docker-compose.yml logs --no-color --tail=100 oz-init openzaak nrc-init nrc-web nrc-celery nrc-beat flowable-init keycloak acl bff projection-db event-subscriber projection-api 2>&1 || true
       - name: Tear down
         if: always()
         run: make down

Makefile

@@ -10,7 +10,7 @@ COMPOSE    := infra/docker-compose.yml
 # Long-running services with a healthcheck — the smoke polls these for readiness
 # (infra/wait-healthy.sh). One-shot init jobs (oz-init, nrc-init, flowable-init)
 # are not polled; they only need to have run. See docs/runbooks/gitea-actions-gotchas.md.
-WAIT_SVCS  := openzaak nrc-web acl bff
+WAIT_SVCS  := openzaak nrc-web acl bff event-subscriber projection-api
 # Config files (OpenZaak data.yaml, Keycloak realms, Flowable BPMN) are streamed
 # into external named volumes via `docker cp` (infra/seed-config.sh) instead of
 # bind-mounted, because bind mounts don't reach sibling containers on the
@@ -43,7 +43,7 @@ export DOCKER_HOST := unix://$(PODMAN_SOCK)
 endif
 endif
 
-.PHONY: ci lint build unit mutation integration verify verify-up verify-acl verify-nrc verify-notifications smoke up down local local-down changelog openzaak-up openzaak-smoke openzaak-seed openzaak-down stack-up stack-smoke stack-down keycloak-up keycloak-smoke keycloak-down flowable-up flowable-smoke flowable-down help
+.PHONY: ci lint build unit mutation integration verify verify-up verify-acl verify-nrc verify-projection verify-notifications smoke up down local local-down changelog openzaak-up openzaak-smoke openzaak-seed openzaak-down stack-up stack-smoke stack-down keycloak-up keycloak-smoke keycloak-down flowable-up flowable-smoke flowable-down help
 
 ## ci: run the full pipeline — lint, build, unit, mutation, verify (mirrors Gitea Actions)
 ## `verify` is the live-stack stage (full stack up once → ACL + notification checks).
@@ -61,14 +61,15 @@ build:
 unit:
 	dotnet test $(SLN) -c Release --filter "Category!=Integration"
 
-## mutation: run the Stryker.NET ratchet on the ACL (fails below the recorded baseline)
+## mutation: run the Stryker.NET ratchet on each service with branching logic (fails below baseline)
 # Stryker is pinned as a local dotnet tool (.config/dotnet-tools.json); `tool restore`
-# makes `make mutation` work from a fresh clone. Config + break threshold (the ratchet,
+# makes `make mutation` work from a fresh clone. Each service owns its config + break
-# CLAUDE.md §5) live in services/acl/stryker-config.json. The ACL is the first service
+# threshold (the ratchet, CLAUDE.md §5): services/acl/stryker-config.json and
-# with branching logic, so it sets the repo-wide baseline; later slices ratchet it up.
+# services/event-subscriber/stryker-config.json. Scores never regress below baseline.
 mutation:
 	dotnet tool restore
 	cd services/acl && dotnet stryker
+	cd services/event-subscriber && dotnet stryker
 
 ## smoke: seed config, bring the whole stack up, wait for health-checked services, tear down
 # SEED populates the external config volumes first (upstream images used verbatim;
@@ -130,7 +131,12 @@ verify-acl:
 verify-nrc:
 	bash infra/run-notification-check.sh
 
-## verify: local mirror of the CI verify-stack job — full stack up once, both checks,
+## verify-projection: OpenZaak → NRC → Event Subscriber → projection-api end-to-end (S-06),
+## against the already-running stack.
+verify-projection:
+	bash infra/run-projection-check.sh
+
+## verify: local mirror of the CI verify-stack job — full stack up once, all checks,
 ## tear down (always). For fast single-concern local iteration use `integration`
 ## (oz-only) or `verify-notifications` (oz+nrc) instead.
 verify:
@@ -139,7 +145,8 @@ verify:
 	@bash -c 'set -e; rc=0; \
 	  WAIT_TIMEOUT=420 bash infra/wait-healthy.sh $(WAIT_SVCS) \
 	    && bash infra/run-acl-integration.sh \
-	    && bash infra/run-notification-check.sh || rc=$$?; \
+	    && bash infra/run-notification-check.sh \
+	    && bash infra/run-projection-check.sh || rc=$$?; \
 	  docker compose -f $(COMPOSE) down --volumes >/dev/null 2>&1; \
 	  docker volume rm -f $(CFG_VOLS) >/dev/null 2>&1; \
 	  exit $$rc'

docs/architecture/adr-0008-read-projection-store.md

@@ -0,0 +1,89 @@
+# ADR-0008: The read projection — a shared, rebuildable store with a writer and a reader
+
+- **Status:** Accepted
+- **Date:** 2026-06-30
+- **Deciders:** Respellion engineering
+- **Relates to:** S-06 (#7); builds on ADR-0001 (loose coupling), ADR-0007 (#56, OZ→NRC wiring); first EF Core usage in the repo
+
+## Context
+
+S-06 (#7) adds the upstream event path's destination: an **Event Subscriber** that consumes
+NRC notifications and a **read projection** the openbaar register reads. The walking-skeleton
+projection (PRD §8.4) holds one row per zaak — `id`, `bsn`, `naam_placeholder`, `status` —
+and must be **idempotent** (NRC redelivers and reorders, CLAUDE.md §8.6) and **rebuildable**
+(a derived artefact, never a write-only source of truth).
+
+Two design questions had no obvious answer:
+
+1. **Where does `bsn` come from?** The NRC `zaken`/`zaak`/`create` notification carries only the
+   zaak URL plus the fixed `kenmerken` (`bronorganisatie`, `zaaktype`, `vertrouwelijkheidaanduiding`).
+   It does **not** carry the bsn. Reading it means calling a ZGW API — which **only the ACL** may
+   do (CLAUDE.md §8.1). The issue's "Touches" lists only `event-subscriber` + `projection-api`,
+   not the ACL.
+2. **Who owns the projection schema?** The subscriber writes the projection; the projection-api
+   reads it. CLAUDE.md §8.5 says "no direct DB access across services; each service owns its
+   schema." Two deployables on one table looks like a violation.
+
+## Decision
+
+**One Postgres database is the read projection. The Event Subscriber writes it (projector) and
+the projection-api reads it (query); both are processes of the single "Read Projection" bounded
+context and share one schema, defined in a shared `Projection.ReadModel` library. `bsn` is
+deferred.**
+
+- **Schema ownership.** The read model — `register_projection` plus the subscriber's
+  `processed_notifications` log — lives in `services/projection-api/Projection.ReadModel`
+  (EF Core + Npgsql). Both services reference it. This is the textbook CQRS read-model split
+  (one writer, one reader over one derived store), **not** the cross-*domain* DB reach §8.5
+  forbids: no domain owns write-state here; the projection is rebuildable (§8.4). §8.5 still
+  holds for every domain database.
+- **Idempotency** is the primary key on `processed_notifications.key` (a deterministic key
+  derived from the immutable notification content). A duplicate insert raises a unique violation,
+  caught and reported as "already recorded", so the duplicate never reaches the projection. The
+  projection upsert is itself idempotent on the zaak id, a second line of defence.
+- **Rebuild replays the log, not OpenZaak.** `POST /admin/rebuild` clears `register_projection`
+  and reprojects every row in `processed_notifications`. So "rebuildable" needs **no** ZGW access
+  (§8.1) and no ACL dependency — keeping S-06 within its stated scope.
+- **`bsn` and `naam_placeholder` are deferred.** They are columns (nullable) but the minimal slice
+  populates only `id` + `status` (`INGEDIEND`) from the notification. Populating personal data
+  requires reading the zaak **through the ACL** (§8.1) and is its own follow-up; the column shape
+  is in place so that change is additive.
+- **New dependency: EF Core 10 + `Npgsql.EntityFrameworkCore.PostgreSQL`.** What it gives us: a
+  migrated relational schema, LINQ queries, and a clean port implementation. What we'd write
+  instead: hand-rolled SQL + a migration runner. Risk: ORM complexity and an extra dependency
+  graph — bounded here to a tiny two-table read model. `dotnet-ef` is pinned as a local tool for
+  migrations; `NuGetAuditMode=direct` keeps EF's design-time-only tooling transitive out of the
+  audited, shipped graph.
+
+The end-to-end path is verified by a runner-safe live-stack smoke (`infra/run-projection-check.sh`,
+the `verify-projection` step of the `verify-stack` job, #58): register an abonnement at the real
+Event Subscriber's callback, create a zaak, assert projection-api serves an `INGEDIEND` row — all
+in-network, reaching services by container IP (ADR-0006/0007).
+
+## Consequences
+
+- **Positive:** the upstream event path reaches a queryable projection; idempotent and rebuildable
+  without OpenZaak; S-06 stays inside its stated touch-set (no ACL change); the projection-api is
+  ready for S-09 to tighten public-safe field filtering.
+- **Negative / deferred:**
+  - `bsn`/`naam_placeholder` stay empty until a follow-up wires zaak reads via the ACL.
+  - The abonnement is registered by the verify harness (by container IP), not provisioned
+    persistently — ADR-0007 already deferred a persistent abonnement, and a single-label service
+    host is not URL-valid for NRC, so persistent registration needs a dotted network alias. Tracked
+    as a follow-up; a plain `make up` therefore needs the abonnement registered before the event
+    path flows.
+  - Two services share one database. Acceptable for a derived read model; revisit if the read and
+    write sides ever need independent scaling or storage.
+
+## Alternatives considered
+
+- **Subscriber reads OpenZaak directly to fill `bsn`** — rejected: breaks §8.1 (only the ACL talks
+  to ZGW) and would need its own ADR to bend the rule.
+- **Extend the ACL with a zaak-read operation, consumed as a library** — viable and §8.1-clean, but
+  it grows S-06 beyond its stated scope (touches the ACL) and pulls personal-data handling forward;
+  deferred to a follow-up.
+- **projection-api owns the DB and exposes an internal write endpoint the subscriber calls** —
+  rejected for the walking skeleton: adds an HTTP hop and a write surface on a read service for no
+  current benefit over a shared, rebuildable read model.
+- **Separate databases for the log and the projection** — rejected as premature: both are the read
+  side's private, rebuildable state; one DB is simpler and still honours §8.5's intent.

docs/demo-script.md

@@ -0,0 +1,35 @@
+# Demo script
+
+A running log of demoable outcomes, one section per slice. Each entry is a short,
+copy-pasteable walkthrough against a local `make up` stack.
+
+---
+
+## S-06 — Event Subscriber + read projection
+
+**Outcome:** a zaak created in OpenZaak flows through NRC to the Event Subscriber, which
+projects it into a rebuildable read projection the projection-api serves.
+
+**The path:** OpenZaak → (notification) NRC → (abonnement callback) Event Subscriber →
+`register_projection` → projection-api `GET /register`.
+
+```bash
+# 1. Bring the full stack up (seeds config, builds our services, waits for health).
+make up
+
+# 2. Register the Event Subscriber's abonnement and create a zaak, then read it back.
+#    (The verify-projection check does exactly this end-to-end and asserts the result.)
+make verify-projection            # → "OK — projection-api serves zaak <uuid> with status INGEDIEND"
+
+# 3. Observe the projection directly via the read API (host port 8120).
+curl -fsS http://localhost:8120/register | jq
+# → [ { "id": "<zaak-uuid>", "status": "INGEDIEND", "bsn": null, "naamPlaceholder": null } ]
+
+# 4. Idempotency + rebuild: replays don't duplicate; a rebuild repopulates from the
+#    notification log (no OpenZaak access needed — ADR-0008).
+curl -fsS -X POST http://localhost:8110/admin/rebuild   # Event Subscriber, host port 8110
+curl -fsS http://localhost:8120/register | jq 'length'  # → unchanged
+```
+
+> `bsn` / `naam_placeholder` are deferred (ADR-0008) — the notification doesn't carry them and
+> the subscriber may not read OpenZaak directly (§8.1). They surface in a later slice.

infra/docker-compose.local.yml

@@ -305,10 +305,68 @@ services:
       start_period: 10s
     networks: [cg]
 
+  # ── Read projection (S-06) ────────────────────────────────────────────────
+  projection-db:
+    image: docker.io/library/postgres:16
+    environment:
+      POSTGRES_USER: projection
+      POSTGRES_PASSWORD: projection
+      POSTGRES_DB: projection
+    volumes:
+      - projection-db:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U projection -d projection"]
+      interval: 5s
+      timeout: 3s
+      retries: 10
+    networks: [cg]
+
+  event-subscriber:
+    build:
+      context: ..
+      dockerfile: services/event-subscriber/Dockerfile
+    image: register-referentie/event-subscriber:dev
+    environment:
+      ConnectionStrings__Projection: Host=projection-db;Database=projection;Username=projection;Password=projection
+      EventSubscriber__Webhook__AuthToken: ${NOTIFICATION_WEBHOOK_TOKEN:-Bearer big-reference-notifications}
+    ports:
+      - "8110:8080"
+    healthcheck:
+      test: ["CMD", "curl", "-fsS", "http://localhost:8080/health"]
+      interval: 5s
+      timeout: 3s
+      retries: 5
+      start_period: 15s
+    depends_on:
+      projection-db:
+        condition: service_healthy
+    networks: [cg]
+
+  projection-api:
+    build:
+      context: ..
+      dockerfile: services/projection-api/Dockerfile
+    image: register-referentie/projection-api:dev
+    environment:
+      ConnectionStrings__Projection: Host=projection-db;Database=projection;Username=projection;Password=projection
+    ports:
+      - "8120:8080"
+    healthcheck:
+      test: ["CMD", "curl", "-fsS", "http://localhost:8080/health"]
+      interval: 5s
+      timeout: 3s
+      retries: 5
+      start_period: 15s
+    depends_on:
+      projection-db:
+        condition: service_healthy
+    networks: [cg]
+
 volumes:
   oz-db:
   nrc-db:
   flowable-db:
+  projection-db:
 
 networks:
   cg:

infra/docker-compose.yml

@@ -9,6 +9,8 @@
 #   8080  BFF               GET /health → Healthy
 #   8090  Flowable REST     http://localhost:8090/flowable-rest/service/
 #   8100  ACL               GET /health → Healthy  POST /zaken
+#   8110  Event Subscriber  GET /health → Healthy  POST /notifications
+#   8120  projection-api    GET /health → Healthy  GET /register
 #   8180  Keycloak          (admin: admin / admin)
 #
 #   docker compose -f infra/docker-compose.yml up -d --build --wait
@@ -320,10 +322,76 @@ services:
       start_period: 10s
     networks: [cg]
 
+  # ── Read projection (S-06) ────────────────────────────────────────────────
+  # One Postgres DB backing the rebuildable read projection (PRD §8.4): the Event
+  # Subscriber writes it, projection-api reads it. See ADR-0008.
+  projection-db:
+    image: docker.io/library/postgres:16
+    environment:
+      POSTGRES_USER: projection
+      POSTGRES_PASSWORD: projection
+      POSTGRES_DB: projection
+    volumes:
+      - projection-db:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U projection -d projection"]
+      interval: 5s
+      timeout: 3s
+      retries: 10
+    networks: [cg]
+
+  # Consumes NRC notifications (abonnement callback) and projects zaak-created events
+  # into register_projection. Build context is the repo root: it shares the read model
+  # in services/projection-api/Projection.ReadModel.
+  event-subscriber:
+    build:
+      context: ..
+      dockerfile: services/event-subscriber/Dockerfile
+    image: register-referentie/event-subscriber:dev
+    environment:
+      ConnectionStrings__Projection: Host=projection-db;Database=projection;Username=projection;Password=projection
+      # The bearer Open Notificaties must present on the abonnement callback. NRC's
+      # registration probe expects a 401 without it (ADR-0007). Dev-only token.
+      EventSubscriber__Webhook__AuthToken: ${NOTIFICATION_WEBHOOK_TOKEN:-Bearer big-reference-notifications}
+    ports:
+      - "8110:8080"
+    healthcheck:
+      test: ["CMD", "curl", "-fsS", "http://localhost:8080/health"]
+      interval: 5s
+      timeout: 3s
+      retries: 5
+      start_period: 15s
+    depends_on:
+      projection-db:
+        condition: service_healthy
+    networks: [cg]
+
+  # The read side of the projection. Shares Projection.ReadModel, so build context is root.
+  projection-api:
+    build:
+      context: ..
+      dockerfile: services/projection-api/Dockerfile
+    image: register-referentie/projection-api:dev
+    environment:
+      ConnectionStrings__Projection: Host=projection-db;Database=projection;Username=projection;Password=projection
+    ports:
+      - "8120:8080"
+    healthcheck:
+      test: ["CMD", "curl", "-fsS", "http://localhost:8080/health"]
+      interval: 5s
+      timeout: 3s
+      retries: 5
+      start_period: 15s
+    depends_on:
+      projection-db:
+        condition: service_healthy
+    networks: [cg]
+
 volumes:
   oz-db:
   nrc-db:
   flowable-db:
+  projection-db:
   # Config volumes — created and populated out-of-band by infra/seed-config.sh
   # (docker cp), because bind mounts don't reach sibling containers on the CI
   # runner. `external` keeps the names deterministic; the seed step manages them.

infra/run-projection-check.sh

@@ -0,0 +1,68 @@
+#!/usr/bin/env bash
+#
+# Verify the end-to-end read-projection path (S-06) against an ALREADY-RUNNING full stack:
+# OpenZaak → NRC → Event Subscriber → projection → projection-api. Seeds a published BIG
+# zaaktype (idempotent), registers an abonnement on the `zaken` kanaal pointing at the real
+# Event Subscriber's /notifications callback (with the bearer it enforces), creates a zaak,
+# and asserts projection-api serves a row for that zaak with status INGEDIEND.
+#
+# All in-network, reaching services by container IP — single-label hosts aren't URL-valid and
+# the runner can't reach published ports (gitea-actions-gotchas.md §5/§6). Reuses the
+# notification driver to register the abonnement + create the zaak. Does NOT manage the stack
+# lifecycle (the caller owns bring-up + teardown). Plain docker primitives only. See ADR-0007/0008.
+set -euo pipefail
+
+here="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+WEBHOOK_AUTH="${NOTIFICATION_WEBHOOK_TOKEN:-Bearer big-reference-notifications}"
+
+cleanup() { docker rm -f rr-pverify rr-pquery >/dev/null 2>&1 || true; }
+trap cleanup EXIT
+
+ip() { docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' "$1"; }
+
+oz="$(docker ps -q --filter 'name=[-_]openzaak[-_]' | head -1)"
+nrc="$(docker ps -q --filter 'name=nrc-web' | head -1)"
+es="$(docker ps -q --filter 'name=event-subscriber' | head -1)"
+proj="$(docker ps -q --filter 'name=projection-api' | head -1)"
+[ -n "$oz" ] && [ -n "$nrc" ] || { echo "ERROR: OpenZaak and/or NRC not running — bring the stack up first" >&2; exit 1; }
+[ -n "$es" ] && [ -n "$proj" ] || { echo "ERROR: event-subscriber and/or projection-api not running — bring the stack up first" >&2; exit 1; }
+net="$(docker inspect -f '{{range $k,$_ := .NetworkSettings.Networks}}{{$k}}{{"\n"}}{{end}}' "$oz" | head -1)"
+oz_ip="$(ip "$oz")"; nrc_ip="$(ip "$nrc")"; es_ip="$(ip "$es")"; proj_ip="$(ip "$proj")"
+echo ">> network=$net openzaak=$oz_ip nrc=$nrc_ip event-subscriber=$es_ip projection-api=$proj_ip"
+
+echo ">> seeding a published BIG zaaktype (idempotent)"
+sid="$(docker create --network "$net" -e "OZ_BASE=http://$oz_ip:8000" -e OZ_PUBLISH=1 \
+  python:3-slim python /seed.py)"
+docker cp "$here/openzaak/seed_catalogus.py" "$sid:/seed.py" >/dev/null
+docker start -a "$sid"
+docker rm -f "$sid" >/dev/null
+
+echo ">> registering abonnement at the Event Subscriber + creating a zaak"
+docker rm -f rr-pverify >/dev/null 2>&1 || true
+drv="$(docker create --network "$net" --name rr-pverify \
+  -e "OZ_BASE=http://$oz_ip:8000" -e "NRC_BASE=http://$nrc_ip:8000" \
+  -e "SINK_CALLBACK=http://$es_ip:8080/notifications" -e "SINK_AUTH=$WEBHOOK_AUTH" \
+  python:3-slim python /driver.py)"
+docker cp "$here/verify-notification-driver.py" "$drv:/driver.py" >/dev/null
+docker start -a "$drv"
+zaak_url="$(docker logs rr-pverify 2>/dev/null | sed -n 's/^ZAAK_CREATED //p' | head -1)"
+docker rm -f rr-pverify >/dev/null
+[ -n "$zaak_url" ] || { echo "ERROR: driver did not create a zaak" >&2; exit 1; }
+zaak_uuid="${zaak_url##*/}"
+echo ">> zaak created: $zaak_url"
+
+echo ">> polling projection-api for the projected row (status INGEDIEND)"
+for _ in $(seq 1 30); do
+  body="$(docker run --rm --network "$net" curlimages/curl:latest \
+    -fsS "http://$proj_ip:8080/register/$zaak_uuid" 2>/dev/null || true)"
+  if echo "$body" | grep -q '"INGEDIEND"'; then
+    echo "OK — projection-api serves zaak $zaak_uuid with status INGEDIEND"
+    echo "$body" | cut -c1-300
+    exit 0
+  fi
+  sleep 2
+done
+echo "FAIL — projection-api never served an INGEDIEND row for zaak $zaak_uuid" >&2
+echo "--- event-subscriber log ---" >&2; docker logs "$es" 2>&1 | tail -10 >&2
+echo "--- projection-api log ---" >&2; docker logs "$proj" 2>&1 | tail -10 >&2
+exit 1

mkdocs.yml

@@ -29,7 +29,9 @@ nav:
       - "ADR-0005: Mutation testing": architecture/adr-0005-mutation-testing.md
       - "ADR-0006: ACL integration test provisioning": architecture/adr-0006-integration-test-provisioning.md
       - "ADR-0007: OpenZaak → NRC notification wiring": architecture/adr-0007-notification-wiring.md
+      - "ADR-0008: Read projection store": architecture/adr-0008-read-projection-store.md
   - Working in Gitea: gitea-workflow.md
+  - Demo script: demo-script.md
   - Runbooks:
       - CI: runbooks/ci.md
 

register-referentie.slnx

@@ -11,6 +11,15 @@
     <Project Path="services/bff/Bff.Api/Bff.Api.csproj" />
     <Project Path="services/bff/Bff.Tests/Bff.Tests.csproj" />
   </Folder>
+  <Folder Name="/services/event-subscriber/">
+    <Project Path="services/event-subscriber/EventSubscriber.Api/EventSubscriber.Api.csproj" />
+    <Project Path="services/event-subscriber/EventSubscriber.Application/EventSubscriber.Application.csproj" />
+    <Project Path="services/event-subscriber/EventSubscriber.Tests/EventSubscriber.Tests.csproj" />
+  </Folder>
+  <Folder Name="/services/projection-api/">
+    <Project Path="services/projection-api/Projection.ReadModel/Projection.ReadModel.csproj" />
+    <Project Path="services/projection-api/ProjectionApi.Api/ProjectionApi.Api.csproj" />
+  </Folder>
   <Folder Name="/tests/">
     <Project Path="tests/acceptance/Acceptance.csproj" />
   </Folder>

services/event-subscriber/Dockerfile

@@ -0,0 +1,32 @@
+# Multi-stage build for the Event Subscriber service (.NET 10).
+# Build context is services/event-subscriber, but it references the shared read model in
+# services/projection-api, so the context is the repo root (see infra/docker-compose.yml).
+FROM mcr.microsoft.com/dotnet/sdk:10.0 AS build
+WORKDIR /src
+
+# Restore first (cached unless .csproj files change).
+COPY services/event-subscriber/EventSubscriber.Api/EventSubscriber.Api.csproj services/event-subscriber/EventSubscriber.Api/
+COPY services/event-subscriber/EventSubscriber.Application/EventSubscriber.Application.csproj services/event-subscriber/EventSubscriber.Application/
+COPY services/projection-api/Projection.ReadModel/Projection.ReadModel.csproj services/projection-api/Projection.ReadModel/
+RUN dotnet restore services/event-subscriber/EventSubscriber.Api/EventSubscriber.Api.csproj
+
+COPY services/event-subscriber/ services/event-subscriber/
+COPY services/projection-api/Projection.ReadModel/ services/projection-api/Projection.ReadModel/
+RUN dotnet publish services/event-subscriber/EventSubscriber.Api/EventSubscriber.Api.csproj -c Release -o /app/publish /p:UseAppHost=false
+
+FROM mcr.microsoft.com/dotnet/aspnet:10.0 AS runtime
+WORKDIR /app
+
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends curl \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY --from=build /app/publish .
+
+ENV ASPNETCORE_URLS=http://+:8080
+EXPOSE 8080
+
+HEALTHCHECK --interval=5s --timeout=3s --start-period=15s --retries=5 \
+    CMD curl -fsS http://localhost:8080/health || exit 1
+
+ENTRYPOINT ["dotnet", "EventSubscriber.Api.dll"]

services/event-subscriber/EventSubscriber.Api/EventSubscriber.Api.csproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <ItemGroup>
+    <ProjectReference Include="..\EventSubscriber.Application\EventSubscriber.Application.csproj" />
+    <ProjectReference Include="..\..\projection-api\Projection.ReadModel\Projection.ReadModel.csproj" />
+  </ItemGroup>
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+</Project>

services/event-subscriber/EventSubscriber.Api/Program.cs

@@ -0,0 +1,66 @@
+using System.Text.Json;
+using EventSubscriber.Application;
+using Projection.ReadModel;
+
+var builder = WebApplication.CreateBuilder(args);
+
+var connectionString = builder.Configuration.GetConnectionString("Projection")
+    ?? throw new InvalidOperationException("Missing connection string 'ConnectionStrings:Projection'");
+// The exact Authorization header value Open Notificaties sends on each abonnement callback.
+// NRC probes the callback during registration and refuses it unless it returns 401 without
+// this value (ADR-0007), so the webhook enforces it.
+var webhookToken = builder.Configuration["EventSubscriber:Webhook:AuthToken"]
+    ?? throw new InvalidOperationException("Missing configuration 'EventSubscriber:Webhook:AuthToken'");
+
+builder.Services.AddProjectionReadModel(connectionString);
+builder.Services.AddProjectionWriteSide();
+
+var app = builder.Build();
+
+// Apply migrations on start so a fresh stack reaches a usable schema unattended.
+await app.Services.MigrateProjectionAsync();
+
+app.MapGet("/health", () => "Healthy");
+
+// The NRC abonnement callback. Open Notificaties POSTs a notification here; we project it.
+// Auth-on-callback is mandatory: the auth check runs *before* the body is read, so NRC's
+// registration probe (a POST without the configured Authorization, and without a valid
+// notification body) gets the 401 it requires rather than a 400 (ADR-0007).
+app.MapPost("/notifications", async (
+    HttpRequest request,
+    NotificationProjector projector,
+    CancellationToken ct) =>
+{
+    if (request.Headers.Authorization != webhookToken)
+        return Results.Unauthorized();
+
+    var dto = await JsonSerializer.DeserializeAsync<NotificationDto>(
+        request.Body, SerializerOptions, ct);
+    if (dto is null)
+        return Results.BadRequest();
+
+    await projector.HandleAsync(dto.ToNotification(), ct);
+    return Results.NoContent();
+});
+
+// Admin: rebuild the projection from the durable notification log (PRD §8.4 — rebuildable).
+app.MapPost("/admin/rebuild", async (NotificationProjector projector, CancellationToken ct) =>
+{
+    await projector.RebuildAsync(ct);
+    return Results.NoContent();
+});
+
+await app.RunAsync();
+
+/// <summary>The NRC notification body, as Open Notificaties POSTs it. Only the fields the
+/// projection needs are bound; <c>aanmaakdatum</c>/<c>kenmerken</c> are ignored for the minimal slice.</summary>
+public sealed record NotificationDto(string Kanaal, string Resource, string Actie, Uri ResourceUrl)
+{
+    public Notification ToNotification() => new(Kanaal, Resource, Actie, ResourceUrl);
+}
+
+public partial class Program
+{
+    // NRC sends camelCase JSON; match it case-insensitively.
+    private static readonly JsonSerializerOptions SerializerOptions = new(JsonSerializerDefaults.Web);
+}

services/event-subscriber/EventSubscriber.Api/appsettings.json

@@ -0,0 +1,8 @@
+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  }
+}

services/event-subscriber/EventSubscriber.Application/EventSubscriber.Application.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+</Project>

services/event-subscriber/EventSubscriber.Application/Notification.cs

@@ -0,0 +1,30 @@
+namespace EventSubscriber.Application;
+
+/// <summary>
+/// An inbound NRC (Open Notificaties) notification, as Open Notificaties POSTs it to an
+/// abonnement callback. Only the fields the projection needs are modelled; the full ZGW
+/// "Notificatie" resource also carries <c>aanmaakdatum</c> and <c>kenmerken</c> which the
+/// minimal projection ignores (bsn is deferred — see ADR-0008). For a <c>zaken</c>/<c>zaak</c>/<c>create</c>
+/// notification <c>hoofdObject</c> and <c>resourceUrl</c> are both the created zaak's URL.
+/// </summary>
+public sealed record Notification(
+    string Kanaal,
+    string Resource,
+    string Actie,
+    Uri ResourceUrl)
+{
+    /// <summary>The only event the walking-skeleton projection reacts to: a zaak being created.</summary>
+    public bool IsZaakCreated =>
+        Kanaal == "zaken" && Resource == "zaak" && Actie == "create";
+
+    /// <summary>The zaak UUID — the trailing path segment of the resource URL — used as the projection key.</summary>
+    public string ZaakId => ResourceUrl.Segments[^1].Trim('/');
+
+    /// <summary>
+    /// A deterministic dedup key. Open Notificaties carries no notification id and may
+    /// redeliver, so the key is derived from the immutable notification content: two
+    /// deliveries of the same zaak-create collapse to one. (NRC may also deliver
+    /// out of order; the projector tolerates that — order does not change the outcome.)
+    /// </summary>
+    public string IdempotencyKey => $"{Kanaal}:{Resource}:{Actie}:{ResourceUrl}";
+}

services/event-subscriber/EventSubscriber.Application/NotificationProjector.cs

@@ -0,0 +1,38 @@
+namespace EventSubscriber.Application;
+
+/// <summary>
+/// Projects inbound NRC notifications into the read projection. Tolerates duplicate and
+/// out-of-order deliveries (CLAUDE.md §8.6): the notification log dedups, and the projection
+/// upsert is idempotent on the zaak id. Rebuilds the projection by replaying the log.
+/// </summary>
+public sealed class NotificationProjector(INotificationLog log, IProjectionStore store)
+{
+    /// <summary>Handle one inbound notification. Ignores anything that is not a zaak-created event.</summary>
+    public async Task HandleAsync(Notification notification, CancellationToken ct = default)
+    {
+        if (!notification.IsZaakCreated)
+            return;
+
+        var recorded = new RecordedNotification(notification.IdempotencyKey, notification.Actie, notification.ZaakId);
+
+        // Atomic record-or-skip: a duplicate (or concurrent) delivery is recognised and dropped
+        // before it touches the projection, so the projection stays a faithful derived artefact.
+        if (!await log.TryRecordAsync(recorded, ct))
+            return;
+
+        await store.UpsertAsync(ToEntry(recorded), ct);
+    }
+
+    /// <summary>Rebuild the projection from the durable notification log (PRD §8.4).</summary>
+    public async Task RebuildAsync(CancellationToken ct = default)
+    {
+        await store.ClearAsync(ct);
+        foreach (var recorded in await log.AllAsync(ct))
+            await store.UpsertAsync(ToEntry(recorded), ct);
+    }
+
+    /// <summary>The minimal projection row for an accepted notification. A zaak-create maps to
+    /// INGEDIEND; bsn/naam are deferred (ADR-0008).</summary>
+    private static RegisterEntry ToEntry(RecordedNotification recorded)
+        => new(recorded.ZaakId, RegistrationStatus.Ingediend);
+}

services/event-subscriber/EventSubscriber.Application/Ports.cs

@@ -0,0 +1,37 @@
+namespace EventSubscriber.Application;
+
+/// <summary>
+/// The durable log of notifications the subscriber has accepted. It is both the idempotency
+/// guard (a replayed notification is recognised and dropped) and the rebuild source: the
+/// projection is a derived artefact (PRD §8.4) regenerated by replaying this log, so a rebuild
+/// needs no access to OpenZaak (CLAUDE.md §8.1). Implemented in Infrastructure over Postgres.
+/// </summary>
+public interface INotificationLog
+{
+    /// <summary>
+    /// Record a notification. Returns <c>true</c> if it was newly recorded, <c>false</c> if an
+    /// entry with the same key already existed (a duplicate delivery). Must be atomic so that
+    /// concurrent duplicate deliveries cannot both observe <c>true</c>.
+    /// </summary>
+    Task<bool> TryRecordAsync(RecordedNotification notification, CancellationToken ct = default);
+
+    /// <summary>Every accepted notification, for rebuilding the projection.</summary>
+    Task<IReadOnlyList<RecordedNotification>> AllAsync(CancellationToken ct = default);
+}
+
+/// <summary>A notification that has been accepted, retaining what a rebuild needs to recompute its projection row.</summary>
+public sealed record RecordedNotification(string Key, string Actie, string ZaakId);
+
+/// <summary>The read projection store. Owned by the projection bounded context (ADR-0008); the
+/// subscriber writes to it and the projection-api reads it.</summary>
+public interface IProjectionStore
+{
+    /// <summary>Insert or update the row for <see cref="RegisterEntry.Id"/>. Idempotent on the id.</summary>
+    Task UpsertAsync(RegisterEntry entry, CancellationToken ct = default);
+
+    /// <summary>Remove every row — the first step of a rebuild.</summary>
+    Task ClearAsync(CancellationToken ct = default);
+
+    /// <summary>Every projection row (used by tests and the rebuild verification).</summary>
+    Task<IReadOnlyList<RegisterEntry>> AllAsync(CancellationToken ct = default);
+}

services/event-subscriber/EventSubscriber.Application/RegisterEntry.cs

@@ -0,0 +1,20 @@
+namespace EventSubscriber.Application;
+
+/// <summary>
+/// A row of the rebuildable read projection (PRD §8.4). For the minimal slice it carries
+/// the zaak id and a status; <c>Bsn</c> and <c>NaamPlaceholder</c> are part of the schema but
+/// are deferred — the NRC notification does not carry them and the subscriber may not read
+/// OpenZaak directly (CLAUDE.md §8.1). Populating them is a follow-up (ADR-0008).
+/// </summary>
+public sealed record RegisterEntry(
+    string Id,
+    string Status,
+    string? Bsn = null,
+    string? NaamPlaceholder = null);
+
+/// <summary>The projection statuses the walking skeleton knows about.</summary>
+public static class RegistrationStatus
+{
+    /// <summary>A zaak has been created; the registration is submitted.</summary>
+    public const string Ingediend = "INGEDIEND";
+}

services/event-subscriber/EventSubscriber.Tests/EventSubscriber.Tests.csproj

@@ -0,0 +1,25 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.4" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.4" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\EventSubscriber.Application\EventSubscriber.Application.csproj" />
+  </ItemGroup>
+
+</Project>

services/event-subscriber/EventSubscriber.Tests/InMemoryStores.cs

@@ -0,0 +1,42 @@
+using EventSubscriber.Application;
+
+namespace EventSubscriber.Tests;
+
+/// <summary>In-memory stand-ins for the projection store and notification log, so the
+/// projector's behaviour is exercised without Postgres (hand-written stubs, the repo's
+/// convention — no mocking library).</summary>
+internal sealed class InMemoryNotificationLog : INotificationLog
+{
+    private readonly Dictionary<string, RecordedNotification> _byKey = [];
+
+    public Task<bool> TryRecordAsync(RecordedNotification notification, CancellationToken ct = default)
+        => Task.FromResult(_byKey.TryAdd(notification.Key, notification));
+
+    public Task<IReadOnlyList<RecordedNotification>> AllAsync(CancellationToken ct = default)
+        => Task.FromResult<IReadOnlyList<RecordedNotification>>([.. _byKey.Values]);
+}
+
+internal sealed class InMemoryProjectionStore : IProjectionStore
+{
+    private readonly Dictionary<string, RegisterEntry> _byId = [];
+
+    /// <summary>How many times a write was attempted — lets a test prove a deduped delivery
+    /// never reaches the store (an idempotent upsert hides the difference in row count alone).</summary>
+    public int UpsertCount { get; private set; }
+
+    public Task UpsertAsync(RegisterEntry entry, CancellationToken ct = default)
+    {
+        UpsertCount++;
+        _byId[entry.Id] = entry;
+        return Task.CompletedTask;
+    }
+
+    public Task ClearAsync(CancellationToken ct = default)
+    {
+        _byId.Clear();
+        return Task.CompletedTask;
+    }
+
+    public Task<IReadOnlyList<RegisterEntry>> AllAsync(CancellationToken ct = default)
+        => Task.FromResult<IReadOnlyList<RegisterEntry>>([.. _byId.Values]);
+}

services/event-subscriber/EventSubscriber.Tests/NotificationProjectorTests.cs

@@ -0,0 +1,89 @@
+using EventSubscriber.Application;
+
+namespace EventSubscriber.Tests;
+
+/// <summary>Behaviour of the projector that turns NRC notifications into projection rows.
+/// The walking skeleton reacts only to a zaak being created (status INGEDIEND) and must
+/// tolerate duplicate and out-of-order deliveries (CLAUDE.md §8.6).</summary>
+public sealed class NotificationProjectorTests
+{
+    private const string ZaakUrl = "http://openzaak:8000/zaken/api/v1/zaken/11111111-1111-1111-1111-111111111111";
+
+    private readonly InMemoryNotificationLog _log = new();
+    private readonly InMemoryProjectionStore _store = new();
+
+    private NotificationProjector Projector() => new(_log, _store);
+
+    private static Notification ZaakCreated(string url = ZaakUrl)
+        => new("zaken", "zaak", "create", new Uri(url));
+
+    [Fact]
+    public async Task creating_a_zaak_writes_one_row_with_status_ingediend()
+    {
+        await Projector().HandleAsync(ZaakCreated());
+
+        var entry = Assert.Single(await _store.AllAsync());
+        Assert.Equal("11111111-1111-1111-1111-111111111111", entry.Id);
+        Assert.Equal(RegistrationStatus.Ingediend, entry.Status);
+    }
+
+    [Fact]
+    public async Task replaying_the_same_notification_keeps_a_single_row()
+    {
+        var projector = Projector();
+        await projector.HandleAsync(ZaakCreated());
+        await projector.HandleAsync(ZaakCreated());
+
+        Assert.Single(await _store.AllAsync());
+    }
+
+    [Fact]
+    public async Task a_replayed_notification_never_reaches_the_projection_store()
+    {
+        var projector = Projector();
+        await projector.HandleAsync(ZaakCreated());
+        await projector.HandleAsync(ZaakCreated());
+
+        // The duplicate is dropped at the log, before the (idempotent) upsert — so the store
+        // is written exactly once. Row count alone can't see this; the upsert count can.
+        Assert.Equal(1, _store.UpsertCount);
+    }
+
+    [Fact]
+    public async Task two_different_zaken_each_get_their_own_row()
+    {
+        var projector = Projector();
+        await projector.HandleAsync(ZaakCreated());
+        await projector.HandleAsync(ZaakCreated(ZaakUrl[..^1] + "2")); // a distinct zaak url
+
+        Assert.Equal(2, (await _store.AllAsync()).Count);
+    }
+
+    [Theory]
+    [InlineData("documenten", "enkelvoudiginformatieobject", "create")] // wrong kanaal + resource
+    [InlineData("documenten", "zaak", "create")]                        // wrong kanaal only
+    [InlineData("zaken", "status", "create")]                           // wrong resource only
+    [InlineData("zaken", "zaak", "update")]                             // wrong actie
+    [InlineData("zaken", "zaak", "destroy")]                            // wrong actie
+    public async Task only_a_zaken_zaak_create_notification_is_projected(string kanaal, string resource, string actie)
+    {
+        await Projector().HandleAsync(new Notification(kanaal, resource, actie, new Uri(ZaakUrl)));
+
+        Assert.Empty(await _store.AllAsync());
+    }
+
+    [Fact]
+    public async Task rebuild_clears_stale_rows_and_repopulates_from_the_notification_log()
+    {
+        var projector = Projector();
+        await projector.HandleAsync(ZaakCreated());
+        // A stale row that is not backed by any logged notification must not survive a rebuild.
+        await _store.UpsertAsync(new RegisterEntry("stale-9999", RegistrationStatus.Ingediend));
+
+        await projector.RebuildAsync();
+
+        var entry = Assert.Single(await _store.AllAsync());
+        Assert.Equal("11111111-1111-1111-1111-111111111111", entry.Id);
+        Assert.Equal(RegistrationStatus.Ingediend, entry.Status);
+    }
+}

services/event-subscriber/EventSubscriber.slnx

@@ -0,0 +1,4 @@
+<Solution>
+  <Project Path="EventSubscriber.Application/EventSubscriber.Application.csproj" />
+  <Project Path="EventSubscriber.Tests/EventSubscriber.Tests.csproj" />
+</Solution>

services/event-subscriber/stryker-config.json

@@ -0,0 +1,12 @@
+{
+  "stryker-config": {
+    "solution": "EventSubscriber.slnx",
+    "test-projects": ["EventSubscriber.Tests/EventSubscriber.Tests.csproj"],
+    "reporters": ["progress", "html"],
+    "thresholds": {
+      "high": 95,
+      "low": 90,
+      "break": 90
+    }
+  }
+}

services/projection-api/Dockerfile

@@ -0,0 +1,31 @@
+# Multi-stage build for the projection-api service (.NET 10).
+# Build context is the repo root (it shares Projection.ReadModel — see infra/docker-compose.yml).
+FROM mcr.microsoft.com/dotnet/sdk:10.0 AS build
+WORKDIR /src
+
+# Restore first (cached unless .csproj files change).
+COPY services/projection-api/ProjectionApi.Api/ProjectionApi.Api.csproj services/projection-api/ProjectionApi.Api/
+COPY services/projection-api/Projection.ReadModel/Projection.ReadModel.csproj services/projection-api/Projection.ReadModel/
+COPY services/event-subscriber/EventSubscriber.Application/EventSubscriber.Application.csproj services/event-subscriber/EventSubscriber.Application/
+RUN dotnet restore services/projection-api/ProjectionApi.Api/ProjectionApi.Api.csproj
+
+COPY services/projection-api/ services/projection-api/
+COPY services/event-subscriber/EventSubscriber.Application/ services/event-subscriber/EventSubscriber.Application/
+RUN dotnet publish services/projection-api/ProjectionApi.Api/ProjectionApi.Api.csproj -c Release -o /app/publish /p:UseAppHost=false
+
+FROM mcr.microsoft.com/dotnet/aspnet:10.0 AS runtime
+WORKDIR /app
+
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends curl \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY --from=build /app/publish .
+
+ENV ASPNETCORE_URLS=http://+:8080
+EXPOSE 8080
+
+HEALTHCHECK --interval=5s --timeout=3s --start-period=15s --retries=5 \
+    CMD curl -fsS http://localhost:8080/health || exit 1
+
+ENTRYPOINT ["dotnet", "ProjectionApi.Api.dll"]

services/projection-api/Projection.ReadModel/DesignTimeProjectionDbContextFactory.cs

@@ -0,0 +1,18 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Design;
+
+namespace Projection.ReadModel;
+
+/// <summary>Lets <c>dotnet ef migrations</c> build the context at design time without a running
+/// database or the host's DI. The connection string is a placeholder — migrations only need the
+/// provider to emit Postgres-shaped SQL.</summary>
+public sealed class DesignTimeProjectionDbContextFactory : IDesignTimeDbContextFactory<ProjectionDbContext>
+{
+    public ProjectionDbContext CreateDbContext(string[] args)
+    {
+        var options = new DbContextOptionsBuilder<ProjectionDbContext>()
+            .UseNpgsql("Host=localhost;Database=projection;Username=projection;Password=projection")
+            .Options;
+        return new ProjectionDbContext(options);
+    }
+}

services/projection-api/Projection.ReadModel/EfNotificationLog.cs

@@ -0,0 +1,39 @@
+using EventSubscriber.Application;
+using Microsoft.EntityFrameworkCore;
+
+namespace Projection.ReadModel;
+
+/// <summary>EF Core implementation of the notification log. Idempotency is enforced atomically
+/// by the primary key on <c>key</c>: a duplicate insert raises a unique violation, which is
+/// caught and reported as "already recorded" rather than failing the request.</summary>
+public sealed class EfNotificationLog(ProjectionDbContext db) : INotificationLog
+{
+    public async Task<bool> TryRecordAsync(RecordedNotification notification, CancellationToken ct = default)
+    {
+        db.ProcessedNotifications.Add(new ProcessedNotificationRow
+        {
+            Key = notification.Key,
+            Actie = notification.Actie,
+            ZaakId = notification.ZaakId,
+            ReceivedAt = DateTimeOffset.UtcNow,
+        });
+
+        try
+        {
+            await db.SaveChangesAsync(ct);
+            return true;
+        }
+        catch (DbUpdateException)
+        {
+            // Already recorded by an earlier (or concurrent) delivery — drop this duplicate.
+            db.ChangeTracker.Clear();
+            return false;
+        }
+    }
+
+    public async Task<IReadOnlyList<RecordedNotification>> AllAsync(CancellationToken ct = default)
+        => await db.ProcessedNotifications
+            .OrderBy(r => r.ReceivedAt)
+            .Select(r => new RecordedNotification(r.Key, r.Actie, r.ZaakId))
+            .ToListAsync(ct);
+}

services/projection-api/Projection.ReadModel/EfProjectionStore.cs

@@ -0,0 +1,40 @@
+using EventSubscriber.Application;
+using Microsoft.EntityFrameworkCore;
+
+namespace Projection.ReadModel;
+
+/// <summary>EF Core implementation of the projection store over <see cref="ProjectionDbContext"/>.</summary>
+public sealed class EfProjectionStore(ProjectionDbContext db) : IProjectionStore
+{
+    public async Task UpsertAsync(RegisterEntry entry, CancellationToken ct = default)
+    {
+        var row = await db.RegisterEntries.FindAsync([entry.Id], ct);
+        if (row is null)
+        {
+            db.RegisterEntries.Add(new RegisterEntryRow
+            {
+                Id = entry.Id,
+                Status = entry.Status,
+                Bsn = entry.Bsn,
+                NaamPlaceholder = entry.NaamPlaceholder,
+            });
+        }
+        else
+        {
+            row.Status = entry.Status;
+            row.Bsn = entry.Bsn;
+            row.NaamPlaceholder = entry.NaamPlaceholder;
+        }
+
+        await db.SaveChangesAsync(ct);
+    }
+
+    public async Task ClearAsync(CancellationToken ct = default)
+        => await db.RegisterEntries.ExecuteDeleteAsync(ct);
+
+    public async Task<IReadOnlyList<RegisterEntry>> AllAsync(CancellationToken ct = default)
+        => await db.RegisterEntries
+            .OrderBy(r => r.Id)
+            .Select(r => new RegisterEntry(r.Id, r.Status, r.Bsn, r.NaamPlaceholder))
+            .ToListAsync(ct);
+}

services/projection-api/Projection.ReadModel/Migrations/20260630125055_InitialProjection.Designer.cs

@@ -0,0 +1,79 @@
+// <auto-generated />
+using System;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Storage.ValueConversion;
+using Npgsql.EntityFrameworkCore.PostgreSQL.Metadata;
+using Projection.ReadModel;
+
+#nullable disable
+
+namespace Projection.ReadModel.Migrations
+{
+    [DbContext(typeof(ProjectionDbContext))]
+    [Migration("20260630125055_InitialProjection")]
+    partial class InitialProjection
+    {
+        /// <inheritdoc />
+        protected override void BuildTargetModel(ModelBuilder modelBuilder)
+        {
+#pragma warning disable 612, 618
+            modelBuilder
+                .HasAnnotation("ProductVersion", "10.0.0")
+                .HasAnnotation("Relational:MaxIdentifierLength", 63);
+
+            NpgsqlModelBuilderExtensions.UseIdentityByDefaultColumns(modelBuilder);
+
+            modelBuilder.Entity("Projection.ReadModel.ProcessedNotificationRow", b =>
+                {
+                    b.Property<string>("Key")
+                        .HasColumnType("text")
+                        .HasColumnName("key");
+
+                    b.Property<string>("Actie")
+                        .IsRequired()
+                        .HasColumnType("text")
+                        .HasColumnName("actie");
+
+                    b.Property<DateTimeOffset>("ReceivedAt")
+                        .HasColumnType("timestamp with time zone")
+                        .HasColumnName("received_at");
+
+                    b.Property<string>("ZaakId")
+                        .IsRequired()
+                        .HasColumnType("text")
+                        .HasColumnName("zaak_id");
+
+                    b.HasKey("Key");
+
+                    b.ToTable("processed_notifications", (string)null);
+                });
+
+            modelBuilder.Entity("Projection.ReadModel.RegisterEntryRow", b =>
+                {
+                    b.Property<string>("Id")
+                        .HasColumnType("text")
+                        .HasColumnName("id");
+
+                    b.Property<string>("Bsn")
+                        .HasColumnType("text")
+                        .HasColumnName("bsn");
+
+                    b.Property<string>("NaamPlaceholder")
+                        .HasColumnType("text")
+                        .HasColumnName("naam_placeholder");
+
+                    b.Property<string>("Status")
+                        .IsRequired()
+                        .HasColumnType("text")
+                        .HasColumnName("status");
+
+                    b.HasKey("Id");
+
+                    b.ToTable("register_projection", (string)null);
+                });
+#pragma warning restore 612, 618
+        }
+    }
+}

services/projection-api/Projection.ReadModel/Migrations/20260630125055_InitialProjection.cs

@@ -0,0 +1,53 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace Projection.ReadModel.Migrations
+{
+    /// <inheritdoc />
+    public partial class InitialProjection : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateTable(
+                name: "processed_notifications",
+                columns: table => new
+                {
+                    key = table.Column<string>(type: "text", nullable: false),
+                    actie = table.Column<string>(type: "text", nullable: false),
+                    zaak_id = table.Column<string>(type: "text", nullable: false),
+                    received_at = table.Column<DateTimeOffset>(type: "timestamp with time zone", nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_processed_notifications", x => x.key);
+                });
+
+            migrationBuilder.CreateTable(
+                name: "register_projection",
+                columns: table => new
+                {
+                    id = table.Column<string>(type: "text", nullable: false),
+                    status = table.Column<string>(type: "text", nullable: false),
+                    bsn = table.Column<string>(type: "text", nullable: true),
+                    naam_placeholder = table.Column<string>(type: "text", nullable: true)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_register_projection", x => x.id);
+                });
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropTable(
+                name: "processed_notifications");
+
+            migrationBuilder.DropTable(
+                name: "register_projection");
+        }
+    }
+}

services/projection-api/Projection.ReadModel/Migrations/ProjectionDbContextModelSnapshot.cs

@@ -0,0 +1,76 @@
+// <auto-generated />
+using System;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Storage.ValueConversion;
+using Npgsql.EntityFrameworkCore.PostgreSQL.Metadata;
+using Projection.ReadModel;
+
+#nullable disable
+
+namespace Projection.ReadModel.Migrations
+{
+    [DbContext(typeof(ProjectionDbContext))]
+    partial class ProjectionDbContextModelSnapshot : ModelSnapshot
+    {
+        protected override void BuildModel(ModelBuilder modelBuilder)
+        {
+#pragma warning disable 612, 618
+            modelBuilder
+                .HasAnnotation("ProductVersion", "10.0.0")
+                .HasAnnotation("Relational:MaxIdentifierLength", 63);
+
+            NpgsqlModelBuilderExtensions.UseIdentityByDefaultColumns(modelBuilder);
+
+            modelBuilder.Entity("Projection.ReadModel.ProcessedNotificationRow", b =>
+                {
+                    b.Property<string>("Key")
+                        .HasColumnType("text")
+                        .HasColumnName("key");
+
+                    b.Property<string>("Actie")
+                        .IsRequired()
+                        .HasColumnType("text")
+                        .HasColumnName("actie");
+
+                    b.Property<DateTimeOffset>("ReceivedAt")
+                        .HasColumnType("timestamp with time zone")
+                        .HasColumnName("received_at");
+
+                    b.Property<string>("ZaakId")
+                        .IsRequired()
+                        .HasColumnType("text")
+                        .HasColumnName("zaak_id");
+
+                    b.HasKey("Key");
+
+                    b.ToTable("processed_notifications", (string)null);
+                });
+
+            modelBuilder.Entity("Projection.ReadModel.RegisterEntryRow", b =>
+                {
+                    b.Property<string>("Id")
+                        .HasColumnType("text")
+                        .HasColumnName("id");
+
+                    b.Property<string>("Bsn")
+                        .HasColumnType("text")
+                        .HasColumnName("bsn");
+
+                    b.Property<string>("NaamPlaceholder")
+                        .HasColumnType("text")
+                        .HasColumnName("naam_placeholder");
+
+                    b.Property<string>("Status")
+                        .IsRequired()
+                        .HasColumnType("text")
+                        .HasColumnName("status");
+
+                    b.HasKey("Id");
+
+                    b.ToTable("register_projection", (string)null);
+                });
+#pragma warning restore 612, 618
+        }
+    }
+}

services/projection-api/Projection.ReadModel/Projection.ReadModel.csproj

@@ -0,0 +1,28 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <!-- Audit only the packages we choose directly. The one flagged transitive
+         (System.Security.Cryptography.Xml, NU1903) comes via EF Core's design-time
+         migration tooling (Microsoft.EntityFrameworkCore.Design, PrivateAssets=all) and
+         is never shipped at runtime — it is out of our control to upgrade. -->
+    <NuGetAuditMode>direct</NuGetAuditMode>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\event-subscriber\EventSubscriber.Application\EventSubscriber.Application.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="10.0.0" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.Relational" Version="10.0.0" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="10.0.0">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+    <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="10.0.0" />
+  </ItemGroup>
+
+</Project>

services/projection-api/Projection.ReadModel/ProjectionDbContext.cs

@@ -0,0 +1,59 @@
+using Microsoft.EntityFrameworkCore;
+
+namespace Projection.ReadModel;
+
+/// <summary>
+/// The read projection's persistence. This single store is the system's rebuildable read model
+/// (PRD §8.4): the Event Subscriber writes to it (projector) and the projection-api reads it
+/// (query). Both processes are the one "Read Projection" bounded context and share this schema —
+/// not a cross-domain DB share (ADR-0008 reconciles this with CLAUDE.md §8.5).
+/// </summary>
+public sealed class ProjectionDbContext(DbContextOptions<ProjectionDbContext> options) : DbContext(options)
+{
+    /// <summary>The public-facing register rows (public-safe filtering is tightened in S-09).</summary>
+    public DbSet<RegisterEntryRow> RegisterEntries => Set<RegisterEntryRow>();
+
+    /// <summary>The Event Subscriber's durable log of accepted notifications — idempotency guard and rebuild source.</summary>
+    public DbSet<ProcessedNotificationRow> ProcessedNotifications => Set<ProcessedNotificationRow>();
+
+    protected override void OnModelCreating(ModelBuilder modelBuilder)
+    {
+        modelBuilder.Entity<RegisterEntryRow>(e =>
+        {
+            e.ToTable("register_projection");
+            e.HasKey(r => r.Id);
+            e.Property(r => r.Id).HasColumnName("id");
+            e.Property(r => r.Status).HasColumnName("status").IsRequired();
+            e.Property(r => r.Bsn).HasColumnName("bsn");
+            e.Property(r => r.NaamPlaceholder).HasColumnName("naam_placeholder");
+        });
+
+        modelBuilder.Entity<ProcessedNotificationRow>(e =>
+        {
+            e.ToTable("processed_notifications");
+            e.HasKey(r => r.Key);
+            e.Property(r => r.Key).HasColumnName("key");
+            e.Property(r => r.Actie).HasColumnName("actie").IsRequired();
+            e.Property(r => r.ZaakId).HasColumnName("zaak_id").IsRequired();
+            e.Property(r => r.ReceivedAt).HasColumnName("received_at");
+        });
+    }
+}
+
+/// <summary>A register projection row. <c>Bsn</c>/<c>NaamPlaceholder</c> are deferred (ADR-0008).</summary>
+public sealed class RegisterEntryRow
+{
+    public required string Id { get; set; }
+    public required string Status { get; set; }
+    public string? Bsn { get; set; }
+    public string? NaamPlaceholder { get; set; }
+}
+
+/// <summary>An accepted notification, retained so the projection can be rebuilt without OpenZaak (§8.1).</summary>
+public sealed class ProcessedNotificationRow
+{
+    public required string Key { get; set; }
+    public required string Actie { get; set; }
+    public required string ZaakId { get; set; }
+    public DateTimeOffset ReceivedAt { get; set; }
+}

services/projection-api/Projection.ReadModel/ServiceCollectionExtensions.cs

@@ -0,0 +1,30 @@
+using EventSubscriber.Application;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Projection.ReadModel;
+
+public static class ServiceCollectionExtensions
+{
+    /// <summary>Register the projection <see cref="ProjectionDbContext"/> against Postgres.</summary>
+    public static IServiceCollection AddProjectionReadModel(this IServiceCollection services, string connectionString)
+        => services.AddDbContext<ProjectionDbContext>(o => o.UseNpgsql(connectionString));
+
+    /// <summary>Register the write-side ports (projector store + notification log) used by the Event Subscriber.</summary>
+    public static IServiceCollection AddProjectionWriteSide(this IServiceCollection services)
+    {
+        services.AddScoped<IProjectionStore, EfProjectionStore>();
+        services.AddScoped<INotificationLog, EfNotificationLog>();
+        services.AddScoped<NotificationProjector>();
+        return services;
+    }
+
+    /// <summary>Apply any pending EF migrations. Called once on service start so a fresh stack
+    /// reaches a usable schema without a manual migration step (DoD: compose up reaches green).</summary>
+    public static async Task MigrateProjectionAsync(this IServiceProvider services, CancellationToken ct = default)
+    {
+        await using var scope = services.CreateAsyncScope();
+        var db = scope.ServiceProvider.GetRequiredService<ProjectionDbContext>();
+        await db.Database.MigrateAsync(ct);
+    }
+}

services/projection-api/ProjectionApi.Api/Program.cs

@@ -0,0 +1,43 @@
+using Microsoft.EntityFrameworkCore;
+using Projection.ReadModel;
+
+var builder = WebApplication.CreateBuilder(args);
+
+var connectionString = builder.Configuration.GetConnectionString("Projection")
+    ?? throw new InvalidOperationException("Missing connection string 'ConnectionStrings:Projection'");
+
+builder.Services.AddProjectionReadModel(connectionString);
+
+var app = builder.Build();
+
+// Ensure the schema exists before serving reads. EF serialises concurrent migrators via the
+// migrations-history lock, so it is safe that the Event Subscriber migrates too.
+await app.Services.MigrateProjectionAsync();
+
+app.MapGet("/health", () => "Healthy");
+
+// The read side of the projection. Public-safe field filtering is tightened in S-09; for now
+// the minimal projection only carries id + status (bsn/naam deferred — ADR-0008).
+app.MapGet("/register", async (ProjectionDbContext db, CancellationToken ct) =>
+{
+    var rows = await db.RegisterEntries
+        .OrderBy(r => r.Id)
+        .Select(r => new RegisterEntryDto(r.Id, r.Status, r.Bsn, r.NaamPlaceholder))
+        .ToListAsync(ct);
+    return Results.Ok(rows);
+});
+
+app.MapGet("/register/{id}", async (string id, ProjectionDbContext db, CancellationToken ct) =>
+{
+    var row = await db.RegisterEntries
+        .Where(r => r.Id == id)
+        .Select(r => new RegisterEntryDto(r.Id, r.Status, r.Bsn, r.NaamPlaceholder))
+        .SingleOrDefaultAsync(ct);
+    return row is null ? Results.NotFound() : Results.Ok(row);
+});
+
+await app.RunAsync();
+
+public sealed record RegisterEntryDto(string Id, string Status, string? Bsn, string? NaamPlaceholder);
+
+public partial class Program;

services/projection-api/ProjectionApi.Api/ProjectionApi.Api.csproj

@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <ItemGroup>
+    <ProjectReference Include="..\Projection.ReadModel\Projection.ReadModel.csproj" />
+  </ItemGroup>
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+</Project>

services/projection-api/ProjectionApi.Api/appsettings.json

@@ -0,0 +1,8 @@
+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  }
+}

tests/acceptance/Acceptance.csproj

@@ -18,6 +18,7 @@
   <ItemGroup>
     <ProjectReference Include="..\..\services\acl\Acl.Application\Acl.Application.csproj" />
     <ProjectReference Include="..\..\services\acl\Acl.Infrastructure\Acl.Infrastructure.csproj" />
+    <ProjectReference Include="..\..\services\event-subscriber\EventSubscriber.Application\EventSubscriber.Application.csproj" />
   </ItemGroup>
 
 </Project>

tests/acceptance/Features/RegisterProjectieBijwerken.feature

@@ -0,0 +1,19 @@
+# language: en
+# Drives S-06 (#7). On a zaak-created notification from NRC the Event Subscriber writes a
+# rebuildable read-projection row (PRD §8.4). This scenario exercises the use case against an
+# in-memory stand-in for the projection store and notification log; real OpenZaak → NRC →
+# subscriber delivery is verified by the live-stack check (verify-projection, ADR-0007/#58).
+Feature: Register-projectie bijwerken op een zaaknotificatie
+  Als openbaar register wil ik dat een aangemaakte zaak in de projectie verschijnt
+  zodat het register de ingediende registratie kan tonen.
+
+  Scenario: Een zaaknotificatie levert een rij met status INGEDIEND
+    Given a zaak is created in OpenZaak with id "11111111-1111-1111-1111-111111111111"
+    When the NRC notification for that zaak is delivered to the event subscriber
+    Then the register projection contains a row for "11111111-1111-1111-1111-111111111111" with status "INGEDIEND"
+
+  Scenario: Dezelfde notificatie tweemaal levert geen duplicaat
+    Given a zaak is created in OpenZaak with id "22222222-2222-2222-2222-222222222222"
+    When the NRC notification for that zaak is delivered to the event subscriber
+    And the same NRC notification is delivered again
+    Then the register projection contains exactly one row for "22222222-2222-2222-2222-222222222222"

tests/acceptance/Steps/RegisterProjectieBijwerkenSteps.cs

@@ -0,0 +1,48 @@
+using Acceptance.Support;
+using EventSubscriber.Application;
+using Reqnroll;
+using Xunit;
+
+namespace Acceptance.Steps;
+
+/// <summary>Bindings for <c>RegisterProjectieBijwerken.feature</c> (S-06). Reqnroll creates
+/// one instance per scenario, so instance fields hold scenario-scoped state.</summary>
+[Binding]
+public sealed class RegisterProjectieBijwerkenSteps
+{
+    private const string ZaakBase = "http://openzaak:8000/zaken/api/v1/zaken/";
+
+    private readonly InMemoryNotificationLog _log = new();
+    private readonly InMemoryProjectionStore _store = new();
+    private readonly NotificationProjector _projector;
+    private Notification? _notification;
+
+    public RegisterProjectieBijwerkenSteps() => _projector = new NotificationProjector(_log, _store);
+
+    [Given("a zaak is created in OpenZaak with id \"(.*)\"")]
+    public void GivenAZaakIsCreatedInOpenZaakWithId(string id)
+        => _notification = new Notification("zaken", "zaak", "create", new Uri(ZaakBase + id));
+
+    [When("the NRC notification for that zaak is delivered to the event subscriber")]
+    public Task WhenTheNotificationIsDelivered()
+        => _projector.HandleAsync(_notification!);
+
+    [When("the same NRC notification is delivered again")]
+    public Task WhenTheSameNotificationIsDeliveredAgain()
+        => _projector.HandleAsync(_notification!);
+
+    [Then("the register projection contains a row for \"(.*)\" with status \"(.*)\"")]
+    public async Task ThenTheProjectionContainsARowWithStatus(string id, string status)
+    {
+        var entry = Assert.Single(await _store.AllAsync());
+        Assert.Equal(id, entry.Id);
+        Assert.Equal(status, entry.Status);
+    }
+
+    [Then("the register projection contains exactly one row for \"(.*)\"")]
+    public async Task ThenTheProjectionContainsExactlyOneRowFor(string id)
+    {
+        await _store.AllAsync();
+        Assert.Single(_store.RowsFor(id));
+    }
+}

tests/acceptance/Support/InMemoryProjectionStores.cs

@@ -0,0 +1,40 @@
+using EventSubscriber.Application;
+
+namespace Acceptance.Support;
+
+/// <summary>In-memory stand-ins for the Event Subscriber's projection store and notification
+/// log, so the S-06 acceptance scenario runs without Postgres (real delivery is a live-stack
+/// check). Mirrors the <c>InMemoryZaakGateway</c> approach used for the ACL scenario.</summary>
+public sealed class InMemoryNotificationLog : INotificationLog
+{
+    private readonly Dictionary<string, RecordedNotification> _byKey = [];
+
+    public Task<bool> TryRecordAsync(RecordedNotification notification, CancellationToken ct = default)
+        => Task.FromResult(_byKey.TryAdd(notification.Key, notification));
+
+    public Task<IReadOnlyList<RecordedNotification>> AllAsync(CancellationToken ct = default)
+        => Task.FromResult<IReadOnlyList<RecordedNotification>>([.. _byKey.Values]);
+}
+
+public sealed class InMemoryProjectionStore : IProjectionStore
+{
+    private readonly Dictionary<string, RegisterEntry> _byId = [];
+
+    public Task UpsertAsync(RegisterEntry entry, CancellationToken ct = default)
+    {
+        _byId[entry.Id] = entry;
+        return Task.CompletedTask;
+    }
+
+    public Task ClearAsync(CancellationToken ct = default)
+    {
+        _byId.Clear();
+        return Task.CompletedTask;
+    }
+
+    public Task<IReadOnlyList<RegisterEntry>> AllAsync(CancellationToken ct = default)
+        => Task.FromResult<IReadOnlyList<RegisterEntry>>([.. _byId.Values]);
+
+    public IReadOnlyList<RegisterEntry> RowsFor(string id)
+        => [.. _byId.Values.Where(e => e.Id == id)];
+}