diff --git a/kits/storage-resize-images/src/event-context.ts b/kits/storage-resize-images/src/event-context.ts
new file mode 100644
index 000000000..35c121f4d
--- /dev/null
+++ b/kits/storage-resize-images/src/event-context.ts
@@ -0,0 +1,71 @@
+/**
+ * Copyright 2026 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import type { StorageEvent } from "firebase-functions/v2/storage";
+
+/**
+ * The 1st gen `EventContext` shape that the extension published inside its
+ * `onCompletion` payload.
+ */
+export interface EventContext {
+  eventId: string;
+  timestamp: string;
+  eventType: string;
+  resource: {
+    service: string;
+    name: string;
+    type?: string;
+  };
+  params: Record<string, string>;
+}
+
+/**
+ * The extension's only trigger was `onFinalize`, so subscribers matching on
+ * `context.eventType` keep matching this value.
+ */
+const STORAGE_FINALIZE_EVENT_TYPE = "google.storage.object.finalize";
+
+const STORAGE_SERVICE = "storage.googleapis.com";
+
+/**
+ * The extension's timestamps had millisecond precision with trailing zeros
+ * trimmed (`...36.06Z`), while 2nd gen event times carry microseconds.
+ */
+function toLegacyTimestamp(time: string | undefined): string {
+  return new Date(time ?? Date.now()).toISOString().replace(/\.?0+Z$/, "Z");
+}
+
+/**
+ * Rebuilds the 1st gen `EventContext` from a 2nd gen `StorageEvent`, so the
+ * `onCompletion` payload keeps the shape the extension published and
+ * `resource.name` still names the uploaded object.
+ *
+ * `params` is always empty: the extension registered
+ * `functions.storage.object()`, whose trigger path has no wildcards.
+ */
+export function toEventContext(event: StorageEvent): EventContext {
+  return {
+    eventId: event.id,
+    timestamp: toLegacyTimestamp(event.time),
+    eventType: STORAGE_FINALIZE_EVENT_TYPE,
+    resource: {
+      service: STORAGE_SERVICE,
+      name: `projects/_/buckets/${event.data.bucket}/objects/${event.data.name}`,
+      type: event.data.kind,
+    },
+    params: {},
+  };
+}
diff --git a/kits/storage-resize-images/src/handlers.ts b/kits/storage-resize-images/src/handlers.ts
index 800ce369e..fe13e8d49 100644
--- a/kits/storage-resize-images/src/handlers.ts
+++ b/kits/storage-resize-images/src/handlers.ts
@@ -20,6 +20,7 @@ import type { File } from "@google-cloud/storage";
 import type * as admin from "firebase-admin";
 import type { StorageEvent } from "firebase-functions/v2/storage";
 import { checkImageContent } from "./content-filter";
+import { toEventContext } from "./event-context";
 import * as events from "./events";
 import { DELETE_IMAGE, type ResolvedResizeImagesConfig } from "./export-config";
 import {
@@ -48,14 +49,7 @@ export async function handleObjectFinalized(
     event.data as unknown as StorageObjectMetadata,
     ctx
   );
-  await events.recordCompletionEvent({
-    context: {
-      eventId: event.id,
-      eventType: event.type,
-      resource: event.source,
-      timestamp: event.time,
-    },
-  });
+  await events.recordCompletionEvent({ context: toEventContext(event) });
 }
 
 export async function generateResizedImageHandler(
diff --git a/kits/storage-resize-images/tests/event-context.test.ts b/kits/storage-resize-images/tests/event-context.test.ts
new file mode 100644
index 000000000..fb8b1fcf4
--- /dev/null
+++ b/kits/storage-resize-images/tests/event-context.test.ts
@@ -0,0 +1,127 @@
+/**
+ * Copyright 2026 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { describe, expect, test } from "vitest";
+import type { StorageEvent } from "firebase-functions/v2/storage";
+import { toEventContext } from "../src/event-context";
+
+const BUCKET = "demo-bucket";
+const OBJECT_NAME = "images/nested/photo.jpg";
+
+const event = {
+  id: "event-1",
+  type: "google.cloud.storage.object.v1.finalized",
+  source: `//storage.googleapis.com/projects/_/buckets/${BUCKET}`,
+  subject: `objects/${OBJECT_NAME}`,
+  time: "2026-01-01T00:00:36.898303Z",
+  specversion: "1.0",
+  bucket: BUCKET,
+  data: {
+    kind: "storage#object",
+    bucket: BUCKET,
+    name: OBJECT_NAME,
+    contentType: "image/jpeg",
+  },
+} as unknown as StorageEvent;
+
+describe("toEventContext", () => {
+  test("rebuilds the 1st gen event context from a 2nd gen event", () => {
+    expect(toEventContext(event)).toEqual({
+      eventId: "event-1",
+      timestamp: "2026-01-01T00:00:36.898Z",
+      eventType: "google.storage.object.finalize",
+      resource: {
+        service: "storage.googleapis.com",
+        name: `projects/_/buckets/${BUCKET}/objects/${OBJECT_NAME}`,
+        type: "storage#object",
+      },
+      params: {},
+    });
+  });
+
+  test.each([
+    ["2026-01-01T00:00:36.898303Z", "2026-01-01T00:00:36.898Z"],
+    ["2026-01-01T00:00:36.060999Z", "2026-01-01T00:00:36.06Z"],
+    ["2026-01-01T00:00:36.000400Z", "2026-01-01T00:00:36Z"],
+  ])(
+    "formats event time %s as the extension's timestamp %s",
+    (time, timestamp) => {
+      expect(toEventContext({ ...event, time }).timestamp).toBe(timestamp);
+    }
+  );
+});
+
+/**
+ * One upload of `in/img-7.jpg` captured from both sides: the 2nd gen finalize
+ * event the kit receives, and the `context` storage-resize-images 0.3.6
+ * published. The extension took `eventId` and `timestamp` from a separate
+ * delivery of the notification, so only their format can match.
+ */
+const CAPTURED_STORAGE_EVENT = {
+  id: "22480302742407839",
+  type: "google.cloud.storage.object.v1.finalized",
+  source: "//storage.googleapis.com/projects/_/buckets/izaak-testing-pairc-ext",
+  subject: "objects/in/img-7.jpg",
+  time: "2026-10-26T15:20:21.630831Z",
+  specversion: "1.0",
+  bucket: "izaak-testing-pairc-ext",
+  data: {
+    kind: "storage#object",
+    bucket: "izaak-testing-pairc-ext",
+    name: "in/img-7.jpg",
+    contentType: "image/jpeg",
+  },
+} as unknown as StorageEvent;
+
+const CAPTURED_EXTENSION_CONTEXT = {
+  eventId: "22480386067619997",
+  eventType: "google.storage.object.finalize",
+  resource: {
+    name: "projects/_/buckets/izaak-testing-pairc-ext/objects/in/img-7.jpg",
+    service: "storage.googleapis.com",
+    type: "storage#object",
+  },
+  timestamp: "2026-10-26T15:20:21.676Z",
+  params: {},
+};
+
+const LEGACY_TIMESTAMP = /^\d{4}-\d\d-\d\dT\d\d:\d\d:\d\d(\.\d{0,2}[1-9])?Z$/;
+const NUMERIC_EVENT_ID = /^\d+$/;
+
+describe("the context the extension actually published", () => {
+  test("matches the extension's eventType, resource and params exactly", () => {
+    const { eventType, resource, params } = toEventContext(
+      CAPTURED_STORAGE_EVENT
+    );
+
+    expect({ eventType, resource, params }).toEqual({
+      eventType: CAPTURED_EXTENSION_CONTEXT.eventType,
+      resource: CAPTURED_EXTENSION_CONTEXT.resource,
+      params: CAPTURED_EXTENSION_CONTEXT.params,
+    });
+  });
+
+  test("matches the format of the extension's eventId and timestamp", () => {
+    const { eventId, timestamp } = toEventContext(CAPTURED_STORAGE_EVENT);
+
+    expect(eventId).toBe("22480302742407839");
+    expect(timestamp).toBe("2026-10-26T15:20:21.63Z");
+    expect(CAPTURED_EXTENSION_CONTEXT.eventId).toMatch(NUMERIC_EVENT_ID);
+    expect(eventId).toMatch(NUMERIC_EVENT_ID);
+    expect(CAPTURED_EXTENSION_CONTEXT.timestamp).toMatch(LEGACY_TIMESTAMP);
+    expect(timestamp).toMatch(LEGACY_TIMESTAMP);
+  });
+});
diff --git a/kits/storage-resize-images/tests/handlers.test.ts b/kits/storage-resize-images/tests/handlers.test.ts
index b7060109c..044f94f09 100644
--- a/kits/storage-resize-images/tests/handlers.test.ts
+++ b/kits/storage-resize-images/tests/handlers.test.ts
@@ -506,19 +506,24 @@ describe("handleObjectFinalized", () => {
     type: "google.cloud.storage.object.v1.finalized",
     source: "//storage.googleapis.com/projects/_/buckets/demo-bucket",
     time: "2026-01-01T00:00:00.000Z",
-    data: mockObject,
+    data: { ...mockObject, kind: "storage#object" },
   } as unknown as Parameters<typeof handleObjectFinalized>[0];
 
   test("brackets the resize with start and completion events", async () => {
     await handleObjectFinalized(storageEvent, makeCtx());
 
-    expect(events.recordStartEvent).toHaveBeenCalledWith(mockObject);
+    expect(events.recordStartEvent).toHaveBeenCalledWith(storageEvent.data);
     expect(events.recordCompletionEvent).toHaveBeenCalledWith({
       context: {
         eventId: "event-1",
-        eventType: "google.cloud.storage.object.v1.finalized",
-        resource: "//storage.googleapis.com/projects/_/buckets/demo-bucket",
-        timestamp: "2026-01-01T00:00:00.000Z",
+        timestamp: "2026-01-01T00:00:00Z",
+        eventType: "google.storage.object.finalize",
+        resource: {
+          service: "storage.googleapis.com",
+          name: "projects/_/buckets/demo-bucket/objects/images/test.jpg",
+          type: "storage#object",
+        },
+        params: {},
       },
     });
   });