Interface Extensions SDK — No way to upload attachments from a custom extension?

Hey 👋

I've been building a custom Interface Extension using the Extensions SDK and ran into what seems like a significant limitation — I can't find any supported way to let users upload a file/attachment directly from within the extension UI.

What I'm trying to do:

I have a custom extension embedded in an Interface page. The workflow requires users to attach a file (e.g. a PDF or image) to a record — ideally triggered from a button or input inside the extension itself.

What I've tried:

• Using a standard HTML <input type="file"> — the file picker opens, but there's no SDK method to then take that file and write it as an attachment to a record field.
• Looking through the @airtable/blocks SDK docs for something like updateRecordAsync with an attachment payload — attachment fields require a URL, not a raw file object. There's no upload endpoint exposed through the SDK.
• Considered uploading to a third-party storage first (e.g. S3 or Cloudinary), getting a public URL, then writing that URL to the attachment field — this works but feels like a significant workaround for what should be a basic operation.

The core problem:

The SDK's updateRecordAsync for attachment fields only accepts an array of objects with a url property. There is no native method to upload a binary file and get back an Airtable-hosted attachment URL. This means a seemingly simple UX — "click here, pick a file, it attaches to this record" — is essentially impossible without a separate file hosting infrastructure.

My questions:

1. Is there something I'm missing in the SDK that allows direct file upload from an extension?
2. Is this a known limitation, and is it on the roadmap?
3. For those who've solved this — what external upload service are you routing through, and how are you handling auth/CORS within the sandboxed extension environment?

This seems like a pretty common use case for anyone building data-entry or document-management workflows inside Interfaces, so I'd love to understand if there's a pattern the community has converged on.

Thanks in advance!