Design 63 turns the mail page into the operator's list with Owly beside it (ADR 0515
to 0519), in six milestones with their issues; its reference mockup is kept beside it,
its data invented. Playbook 10 says how a page is designed before it is built: mockups
with fixed data, the operator picks, the pick is the reference. The as-is of the mail
modules now describes mail reading as delivered, the glossary gains design 63's words,
design 59's milestone 4 is marked replaced, and AGENTS.md allows a design's mockup.
Issues 1855 and 1856.