Images an email's HTML shows with cid: URLs (logos, signatures, pasted
screenshots) were blank. They now come from the server when the email
opens: from the raw message over IMAP, and from the inline attachments
over Microsoft Graph. They reach the sandboxed frame as data URLs, up to
5 MB each and 20 MB per email, and stay hidden rather than broken until
they arrive. The last 100 emails' images are cached while the app runs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>