Expense details and editing

The shared web/desktop UI and native mobile screens use the same expense flow:

• Split between lists the people included in an expense. Each item also shows its split method and names, so different item splits stay clear.
• Guest and Invited appear as small, separate pills beside a name in person pickers. They do not change the participant ID used by expenses.
• The floating action on an expense is Edit, shown only to someone allowed to edit it. Read-only shared expenses show no edit action or comment composer.
• Existing items start collapsed when editing. Open an item to change it; Done stays disabled until its amount is a valid number. Negative discounts remain supported. The final save still checks payments and split totals.
• Paid by includes the converted Group total when currencies differ. The bank total can still be changed, and unchanged payment charges are preserved. Currency pickers show names; amounts retain their proper decimal precision and use symbols or a full currency name instead of an unfamiliar code.

Comments and mentions

Type @ in the comment field and choose a group member by name or username. Web/desktop suggestions support arrow keys, Enter and Escape; mobile uses tappable suggestions. Username lookup uses the existing People search and filters results back to the group's account-holding members. Guests and pending invitees cannot receive account notifications until they join.

Only a selected suggestion adds its participant ID to the existing mentionedParticipantIds request field. Plain text alone does not select a recipient. Editing or deleting a selected tag removes that recipient; text inserted elsewhere preserves it. Up to 20 distinct people can be tagged. Failed posts keep the draft, and an in-flight post disables the composer.

These changes use existing native controls and the current app runtime; they can ship by mobile OTA. Desktop users need a new desktop release. Windows Store publication remains separate from preparing its submission package.