[bmc08gt]

Syncs the contract to flipcash2-protobuf-api@b77bf78f (upstream #151, #152, #154, #155, #156) and adds the 0.21.0 changelog entry. Release as 0.21.0.

This upgrade breaks source for both apps: CashContent.amount became total_amount, and receiver became single_receiver inside a new oneof recipient. Field numbers are unchanged, so the wire format is not affected.

Contract changes

• New paymentrequest.v1.PaymentRequest service: CreatePaymentRequest, GetPaymentRequest, GetChatPaymentRequests, ClosePaymentRequest, MarkPaid. The only kind today is a split in a group chat. It comes with a messaging.v1.PaymentRequestWidget (WidgetContent oneof field 3) and an intent.v1.ChatMetadata.requested_payment (oneof field 6).
• messaging.v1.CashContent: the rename above, plus multi_receiver (oneof field 5, 2 to 10 Payments) and payment_request_id (field 6).
• Chat moderation: SilenceUser, UnsilenceUser, BanUser, UnbanUser, GetRestrictedUsers. Also ViewerState.restrictions (field 3) and ViewerState.Permissions.moderation (field 2).
• Appended enum cases: JoinChatResponse.Result.BANNED = 4 and EnterLobbyResponse.Result.BANNED = 6. Nothing was renumbered.
• Docs only: reaction boosts are allowed in DMs, and ENCRYPTION_REQUIRED covers DMs.

App PRs

Both are drafts. They contain only the scaffolding and stay blocked until 0.21.0 is published and their pins move.

• Android: feat(chat): adopt the flipcash2 0.21.0 contract code-android-app#1840
• iOS: feat(chat): adopt the flipcash2 0.21.0 contract code-ios-app#1125