async-imap, async-pop, mail-send, mail-parser and mail-builder replace MailCore 2. The MailCore 2 and libetpan fetch, build and probe scripts go. HTML bodies render as a sanitized block subset in GPUI; compose uses the Markdown document component. OAuth client IDs come from oauth.env (ignored) or CI secrets. The task list for C12 is rewritten in order. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>