[p70436464-prog]

Closes #1686

Summary

Resolves the money-loss issue where contacts saved via Stellar federation addresses had their memo_type and memo discarded, and returned account_id values were trusted without checksum verification.

Money-Loss Scenario

Exchanges and custodial services rely on federation memos (e.g., account memo IDs) to route incoming payments and deposits to specific user balances. When a user saved a contact by federation address (e.g. user*exchange.com), StreamPay previously discarded the federation memo_type and memo, while allowing users to type a private note into a free-text memo field. Creating payment streams to such contacts without the required on-chain memo causes the exchange to receive funds with no destination metadata, leading to permanent loss or stuck customer funds.

What Was Done

1. Federation Response Validation (app/utils/federation.ts):
   • Validates account_id using full StrKey base32 decoding and CRC-16 XMODEM checksum checks (isValidStellarPublicKey).
   • Validates memo_type against allowed values (text, id, hash).
   • Validates memo format for each type (utf-8 length <= 28 for text, uint64 string for id, 32-byte hex or base64 for hash).
   • Validates stellar_address matches query (case-insensitive).
   • Throws FederationError("...", "INVALID_RESPONSE") on failure.
   • Prevents caching of invalid responses.
2. Memo Separation & Contact Interface (app/contacts/page.tsx):
   • Extended Contact with requiredMemo?: { type: "text" | "id" | "hash"; value: string }, distinct from the user's private memo note.
   • Added getContactPaymentTarget(contact) helper returning { address, memo? }.
   • Contact form displays the required memo in a read-only field with a "Required by <federationAddress>" badge (aria-readonly="true"). The user cannot edit or clear it.
   • Maintained backward compatibility for reading legacy contacts from localStorage.
3. Checksum Verification & Demo Contacts:
   • Reject G-addresses that match length/regex but fail CRC-16 checksum with error "Invalid Stellar address".
   • Updated demo contacts to valid StrKey checksum addresses.

Test Results