diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7ccf64763..689855d76 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -199,8 +199,9 @@ jobs:
       matrix:
         include:
           # Core also builds and installs the reporting wheel/sdist fixtures.
+          # It runs 25-29 minutes on main, so 30 cancelled it on slow runners.
           - lane: core
-            timeout_minutes: 30
+            timeout_minutes: 45
           - lane: process
             timeout_minutes: 15
     services:
diff --git a/src/adcp/types/_forward_compat.py b/src/adcp/types/_forward_compat.py
index a3e8a4f92..42851a573 100644
--- a/src/adcp/types/_forward_compat.py
+++ b/src/adcp/types/_forward_compat.py
@@ -58,7 +58,7 @@
 from pydantic_core import CoreSchema, InitErrorDetails, PydanticCustomError, core_schema
 from pydantic_core.core_schema import ErrorType
 
-from adcp.types.base import AdCPBaseModel
+from adcp.types.base import AdCPBaseModel, NoExplicitNull
 from adcp.types.canonical_creative import CreateMediaBuyRequest as _PublicCreateMediaBuyRequest
 from adcp.types.canonical_creative import PackageRequest as PublicPackageRequest
 from adcp.types.canonical_creative import PackageUpdate as PublicPackageUpdate
@@ -156,6 +156,9 @@
             "identical wire shape, so confirm seller support before relying on it."
         ),
     ),
+    # Optional, not nullable: a JSON null is refused, as on the generated
+    # push_notification_config.operation_id this field mirrors (#1547).
+    NoExplicitNull,
 ]
 
 if TYPE_CHECKING:
diff --git a/tests/test_reporting_webhook_operation_id.py b/tests/test_reporting_webhook_operation_id.py
index 6727ce410..07747ae79 100644
--- a/tests/test_reporting_webhook_operation_id.py
+++ b/tests/test_reporting_webhook_operation_id.py
@@ -220,7 +220,12 @@ def test_reporting_operation_id_constraints_match_push_notification_config() ->
     assert reporting.annotation == push.annotation
     assert [repr(item) for item in reporting.metadata] == [repr(item) for item in push.metadata]
     schema = ReportingWebhook.model_json_schema()["properties"]["operation_id"]
-    assert schema["anyOf"][0] == {
+    push_schema = PushNotificationConfig.model_json_schema()["properties"]["operation_id"]
+    wire_keys = ("type", "minLength", "maxLength", "pattern", "anyOf")
+    assert {key: schema.get(key) for key in wire_keys} == {
+        key: push_schema.get(key) for key in wire_keys
+    }
+    assert {key: schema[key] for key in ("type", "minLength", "maxLength", "pattern")} == {
         "type": "string",
         "minLength": 1,
         "maxLength": 255,
@@ -229,6 +234,18 @@ def test_reporting_operation_id_constraints_match_push_notification_config() ->
     assert "MUST NOT emit `media_buy_delivery`" in schema["description"]
 
 
+def test_reporting_operation_id_refuses_an_explicit_json_null() -> None:
+    """Omitted is fine; a JSON null is not, matching the generated push field."""
+    base = {
+        "url": "https://buyer.example/reporting",
+        "authentication": _AUTHENTICATION,
+        "reporting_frequency": "daily",
+    }
+    assert ReportingWebhook.model_validate_json(json.dumps(base)).operation_id is None
+    with pytest.raises(ValidationError):
+        ReportingWebhook.model_validate_json(json.dumps({**base, "operation_id": None}))
+
+
 @pytest.mark.asyncio
 async def test_stored_registration_correlates_delivery_and_retry(tmp_path: Path) -> None:
     registration = ReportingWebhook(