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The UAB (Universal Announcement Bus) relays stealth announcements across chains via Wormhole. A payment announced on Solana can appear in an Ethereum user’s inbox (and vice versa) without a central indexer.

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How it works

  1. Sender calls announceWithRelay on UABSender (local announce + Wormhole publish)
  2. Wormhole guardians attest the 96-byte payload
  3. Relayer delivers the VAA to UABReceiver on the destination chain
  4. Receiver re-emits a standard Announce event
  5. Recipient scans with the same WASM filter as native announcements
// Build cross-chain relay (Ethereum)
const send = client.prepareStealthSend(metaAddressHex);
const relay = await client.buildAnnounceWithRelayRequest(send);
await walletClient.sendTransaction({
  to: relay.to,
  data: relay.data,
  value: relay.value,  // Wormhole message fee
});

// Or bundled in sendStealthPayment
await client.sendStealthPayment({
  chain: "ethereum",
  recipient,
  amount: parseEther("0.01"),
  relay: true,
});

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Scanning cross-chain outputs

// UAB-only scan
const crossOwned = await client.scanCrossChain();

// Unified inbox (native + UAB when configured)
const inbox = await client.scan({
  chains: ["ethereum"],
  includeCrossChain: true,  // default when UAB is deployed
});
// Each output has source: "native" | "uab"

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Relayer

Off-chain VAA delivery is handled by opaquecash/relayer. The SDK builds and reads announcements; the relayer watches Wormhole and submits VAAs to UABReceiver.

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Wormhole chain IDs

ChainWormhole ID
Solana1
Ethereum2
Exported as WORMHOLE_CHAIN_SOLANA and WORMHOLE_CHAIN_ETHEREUM from @opaquecash/opaque.