diff --git a/infra/openzaak/seed_catalogus.py b/infra/openzaak/seed_catalogus.py
index 1c913c0..a9aa4c6 100644
--- a/infra/openzaak/seed_catalogus.py
+++ b/infra/openzaak/seed_catalogus.py
@@ -18,6 +18,16 @@ SECRET = os.environ.get("OZ_SECRET", "insecure-dev-secret-change-me")
 ZTC = f"{BASE}/catalogi/api/v1"
 RSIN = "517439943"  # elfproef-valid test RSIN
 
+# Opt-in: also publish the zaaktype so OpenZaak's Zaken API accepts a zaak against
+# it (a concept zaaktype is rejected with `not-published`). Off by default — the
+# S-01 compose seed keeps it a concept (ADR-0002). The ACL integration test
+# (S-04a, #46) sets OZ_PUBLISH=1. Publishing requires ≥2 statustypen, ≥1 roltype
+# and ≥1 resultaattype; the resultaattype is validated against the external
+# Selectielijst reference API, so this path needs outbound access to it. See ADR-0006.
+PUBLISH = os.environ.get("OZ_PUBLISH", "").lower() in ("1", "true", "yes")
+SELECTIELIJST = os.environ.get(
+    "OZ_SELECTIELIJST", "https://selectielijst.openzaak.nl/api/v1").rstrip("/")
+
 
 def token():
     b64 = lambda b: base64.urlsafe_b64encode(b).rstrip(b"=")
@@ -52,6 +62,68 @@ def find(path):
     return body.get("results", [])
 
 
+def selectielijst(path):
+    """GET the external Selectielijst reference API (no auth). Used only when publishing."""
+    req = urllib.request.Request(f"{SELECTIELIJST}{path}", headers={"Accept": "application/json"})
+    with urllib.request.urlopen(req, timeout=30) as r:
+        return json.loads(r.read())
+
+
+def publish_zaaktype(zt):
+    """Add the relations OpenZaak requires to publish, then publish (idempotent).
+
+    Publish validation (verified against OpenZaak 1.28.2) demands: ≥2 statustypen
+    (begin + eind), ≥1 roltype, ≥1 resultaattype. A resultaattype needs a
+    Selectielijst `selectielijstklasse` whose procestype matches the zaaktype's
+    `selectielijstProcestype`, plus a `resultaattypeomschrijving`.
+    """
+    have_st = {s.get("volgnummer") for s in find(f"/statustypen?zaaktype={zt['url']}&status=alles")}
+    for volgnummer, omschrijving in [(1, "Ontvangen"), (2, "Afgehandeld")]:
+        if volgnummer not in have_st:
+            st, body = api("POST", "/statustypen", {
+                "omschrijving": omschrijving, "zaaktype": zt["url"], "volgnummer": volgnummer})
+            if st != 201:
+                sys.exit(f"create statustype {volgnummer} -> {st}: {json.dumps(body, indent=2)}")
+            print(f"create statustype {volgnummer} ({omschrijving})")
+
+    if find(f"/roltypen?zaaktype={zt['url']}&status=alles"):
+        print("skip   roltype Aanvrager")
+    else:
+        st, body = api("POST", "/roltypen", {
+            "zaaktype": zt["url"], "omschrijving": "Aanvrager", "omschrijvingGeneriek": "initiator"})
+        if st != 201:
+            sys.exit(f"create roltype -> {st}: {json.dumps(body, indent=2)}")
+        print("create roltype Aanvrager")
+
+    if find(f"/resultaattypen?zaaktype={zt['url']}&status=alles"):
+        print("skip   resultaattype Geregistreerd")
+    else:
+        resultaat = selectielijst("/resultaten?pageSize=1")["results"][0]
+        omschrijvingen = selectielijst("/resultaattypeomschrijvingen")
+        oms = (omschrijvingen if isinstance(omschrijvingen, list) else omschrijvingen["results"])[0]["url"]
+        # The selectielijstklasse and the zaaktype must share a procestype.
+        st, body = api("PATCH", zt["url"], {"selectielijstProcestype": resultaat["procesType"]})
+        if st != 200:
+            sys.exit(f"set procestype -> {st}: {json.dumps(body, indent=2)}")
+        st, body = api("POST", "/resultaattypen", {
+            "zaaktype": zt["url"], "omschrijving": "Geregistreerd",
+            "resultaattypeomschrijving": oms, "selectielijstklasse": resultaat["url"],
+            "archiefnominatie": "blijvend_bewaren",
+            "brondatumArchiefprocedure": {"afleidingswijze": "afgehandeld"},
+        })
+        if st != 201:
+            sys.exit(f"create resultaattype -> {st}: {json.dumps(body, indent=2)}")
+        print("create resultaattype Geregistreerd")
+
+    if zt.get("concept", True):
+        st, body = api("POST", f"{zt['url']}/publish")
+        if st != 200:
+            sys.exit(f"publish zaaktype -> {st}: {json.dumps(body, indent=2)}")
+        print(f"publish zaaktype BIG-REGISTRATIE ({zt['url']})")
+    else:
+        print("skip   publish (already published)")
+
+
 def main():
     # 1. Catalogus
     existing = [c for c in find(f"/catalogussen?domein=BIG") if c.get("domein") == "BIG"]
@@ -121,16 +193,24 @@ def main():
     else:
         print("warn   zaaktype already published; cannot add bsn eigenschap")
 
-    # Intentionally NOT published. Publishing requires roltypen, resultaattypen
-    # and statustypen, which go beyond the "lean / schema-mandatory" zaaktype this
-    # slice asks for; they arrive with the workflow/zaak slices. See ADR-0002.
+    # 4. Optionally publish. By default the zaaktype stays a concept: publishing
+    # requires roltypen, resultaattypen and statustypen, beyond the "lean /
+    # schema-mandatory" zaaktype S-01 asks for (ADR-0002). Set OZ_PUBLISH=1 to add
+    # those relations and publish — needed so a real zaak POST is accepted, which
+    # the ACL integration test (S-04a, #46) exercises. See ADR-0006.
+    if PUBLISH:
+        # Re-fetch: the bsn-eigenschap branch above may hold a stale concept flag.
+        zt = next(z for z in find(f"/zaaktypen?catalogus={cat['url']}&status=alles")
+                  if z.get("identificatie") == "BIG-REGISTRATIE")
+        publish_zaaktype(zt)
 
-    # 4. Verify the JWT client can list the zaaktype (concepts included).
+    # 5. Verify the JWT client can list the zaaktype (concepts included).
     zaaktypen = find(f"/zaaktypen?catalogus={cat['url']}&status=alles")
     names = [z.get("identificatie") for z in zaaktypen]
     print(f"zaaktypen in BIG: {names}")
     assert "BIG-REGISTRATIE" in names, "BIG-REGISTRATIE not listed"
-    print("OK — BIG catalogus seeded (BIG-REGISTRATIE concept + bsn eigenschap)")
+    state = "published" if PUBLISH else "concept"
+    print(f"OK — BIG catalogus seeded (BIG-REGISTRATIE {state} + bsn eigenschap)")
 
 
 if __name__ == "__main__":