Web Push: Custom data key-value pairs not present in the service worker payload

Hi everyone,

I'm implementing Web Push in Adobe Journey Optimizer with the Web SDK, and I'm trying to pass custom metadata to the service worker using the Custom data section of the push content editor. The key-value pairs don't appear in the payload the service worker receives, and I couldn't find official documentation describing how Custom data is handled for the Web platform.

SETUP
- Web SDK (alloy.js) 2.35.0 with pushNotifications configured (vapidPublicKey, appId, trackingDatasetId)
- Official alloyServiceWorker.js served from the site root
- Push channel configuration with the Web platform selected
- Event-triggered journey with a Push action; Custom data added to the content and the journey republished

WHAT I TESTED
To inspect the raw payload before the Adobe service worker processes it, I added a push listener at the top of the service worker file:

self.addEventListener("push", function (event) {
  console.log("[DEBUG]", JSON.stringify(event.data.json(), null, 2));
});

The notification is delivered and displayed correctly, and the payload looks like this (IDs removed):

{
  "web": {
    "title": "...",
    "body": "...",
    "media": null,
    "interaction": { "type": "DEEPLINK", "uri": null },
    "actions": { "buttons": [ { "label": "...", "type": "WEBURL", "uri": "..." } ] }
  },
  "priority": "HIGH",
  "_xdm": {
    "mixins": {
      "_experience": {
        "customerJourneyManagement": { "messageExecution": { ... } },
        "decisioning": { "propositions": [ ... ] }
      }
    }
  }
}

None of the Custom data key-value pairs appear anywhere in the payload.

DOCUMENTATION
The "Design a push notification" page covers iOS, Android and Web, but the Custom data section only states that values are added "depending on your mobile application configuration", and the related notes (adb_media, mutable-content, Notification Service Extension) are mobile-specific. I couldn't find anything describing the Web behavior.

QUESTIONS
1. Is Custom data supported for the Web platform?
2. If it is, where should the values appear in the payload, and is any additional configuration required?
3. If it isn't, what is the recommended way to pass custom metadata to the service worker? For example, query parameters in the click-through URIs?
4. Is there documentation describing the full Web Push payload structure?

Thanks in advance!

Diego