[huangji6693-max]

Summary

Implements a cross-chain bridge payment relay (bridge_pay, BridgeProof, set_bridge_authority) enabling external-chain payments to settle StellarSplit invoices on Stellar.

Closes #343

Key Changes

1. Relay Proof & Authority Configuration:
   • Added BridgeProof struct (invoice_id, source_chain_id, source_tx_hash, sender_address, amount, signature).
   • Added set_bridge_authority(env, admin, authority_pubkey: BytesN<32>) and get_bridge_authority(env) stored under bridge_authority_key() (brg_auth).
2. Signature Verification & Replay Protection (bridge_pay):
   • Computes a domain-separated canonical SHA-256 digest (compute_bridge_proof_digest) over (invoice_id, source_chain_id, source_tx_hash, sender_address, amount) and verifies proof.signature against the stored bridge_authority Ed25519 public key via env.crypto().ed25519_verify.
   • Stores consumed source_tx_hash keys under bridge_consumed_tx_key (("brg_tx", source_tx_hash)) and panics with "AlreadyConsumed" on replay attempts.
3. Payment Flow & Event Integration:
   • Emits BridgePaymentReceived with full proof metadata (payer, source_chain_id, source_tx_hash, sender_address, amount, event_seq).
   • Credits the invoice and triggers automatic release (Self::_release) when the invoice becomes fully funded.
4. Storage Key Snapshot & Migration Note:
   • Registered bridge_authority_key in contracts/split/src/storage_snapshot.rs and updated tests/snapshots/storage_keys.json (collision-free).
5. Unit Tests (issue_343_tests):
   • test_bridge_pay_valid_relay_and_auto_release
   • test_bridge_pay_invalid_signature_rejected
   • test_bridge_pay_replayed_proof_rejected
   • test_bridge_pay_wrong_invoice_rejected
   • test_bridge_pay_wrong_amount_rejected