Turn this request into a design brief

Starting work where the whole goal arrived as one Slack message.

Write a design brief from the notes below, and be explicit about what is missing.

Structure:
- **Problem**: whose problem, how we know, how often it happens.
- **Success**: what changes if this works, stated as something observable.
- **Users and context**: who, on what device, under what pressure.
- **Scope**: what is in, and a firm list of what is out.
- **Constraints**: technical, legal, brand, timeline, existing patterns we must reuse.
- **Open questions**: what nobody has decided yet.

No solution in the brief unless a constraint already fixed it. Where the notes assume a solution, restate it as the underlying problem and flag the assumption. End with the three questions I should answer before any design starts.

Notes:

Briefs and decisions. The work around the design: turning a request into a brief, choosing between options, writing down why.