RFC: Funding Modality

Source PR: #339 · docs/rfcs/funding-modality.md · @CoachCoe

Description

A Funding trait moves value between the user's Polkadot balance and the outside world in both directions, over cash, bank, card, friend, exchange and foreign-chain rails. Consumers declare an intent and watch it; providers declare the modality in their manifest and serve intents addressed to them.

Motivation

PaymentTopUpSource assumes the product already holds the money, so hitting InsufficientBalance is a dead end and there is no path for getting value out at all. Without a declared contract, every provider integration lands as bespoke Host code.

Requirements

• Methods: request, status_subscribe, serve_subscribe (manifest-declared providers only), report.
• Routes are declared statically in the manifest, so the rail list needs no provider code.
• Sessions persist in CoreStorage and survive Host restart.
• Delivered comes only from the runtime's own on-chain observation, never from a provider report.
• The Host owns eligibility, release authorization, and every terminal state.

Tasks

• RFC document body
• Implementation — rust-core
• Implementation — hosts
  • dotli
  • Desktop
  • iOS
  • Android
  • host-cli