Add guide for transferring assets from Ethereum into Polkadot

[brunopgalvao]

Summary

• Add step-by-step guide for bridging assets from Ethereum to Polkadot using ParaSpell XCM SDK and Snowbridge
• Include mermaid sequence diagram showing the complete bridge flow
• Add code snippets for token approval, bridge execution, and querying supported assets
• Include warnings about WETH requirement and foreign asset verification

Testing

This guide was tested end-to-end using Snowbridge's testnet (Sepolia ↔ Paseo) to verify the implementation works correctly before publishing.

Test Environment

Since ParaSpell SDK officially only supports mainnet, I cloned and patched the SDK to work with testnet for verification:

Patches applied to paraspell/xcm-tools clone:

• packages/sdk-pjs/src/ethTransfer/createContext.ts - Changed from hardcoded mainnet to use paseo_sepolia environment
• packages/sdk-pjs/src/ethTransfer/ethTransfer.ts - Added findTokenInEnv() helper to use Snowbridge environment token addresses
• packages/assets/src/assets/search/findAssetInfoBySymbol.ts - Added support for Sepolia chainId (11155111)
• packages/assets/src/maps/assets.json - Added Sepolia WETH token entry
• @snowbridge/api environment - Updated RPC endpoints to working Paseo endpoints

Test Wallets

Network	Address
Ethereum (Sepolia)	0xffb0034DeA8bdE45Df62E957Ad95FA1e6487bB8F
Polkadot Hub Paseo	14zTT2K9YRtEXjv1vjzCevsm1T1LcEqTZnGPd874oJTskk8p

Successful Test Transactions (Ethereum Sepolia)

1. ERC-20 Approval Transaction

   • Approves the Snowbridge Gateway contract to spend WETH tokens
   • Block: 9890440
   • Tx Hash: 0x6a0997b404032fb562fd2c0881898450a5e24cb38cb1c560796de0d3ccc53794

2. Snowbridge Gateway Transaction

   • Calls the Snowbridge Gateway smart contract on Sepolia, which locks the WETH and emits an event for relayers to relay to Bridge Hub on Polkadot
   • Tx Hash: 0x37de492d9e99ab637a25f205a630d68e1336334b284942571b43208c4f95da89
   • Amount: 0.0001 WETH
   • Token: Sepolia WETH (0xfff9976782d46cc05630d1f6ebab18b2324d6b14)
   • Destination: Polkadot Hub Paseo

Verified Receipt on Polkadot Hub Paseo

After approximately 30 minutes, the bridged tokens arrived successfully. Queried via Polkadot.js API:

Checking WETH balance for: 14zTT2K9YRtEXjv1vjzCevsm1T1LcEqTZnGPd874oJTskk8p

=== WETH Balance Found! ===
Raw Balance: 300000000000000
Formatted (18 decimals): 0.0003 WETH

The account received 0.0003 WETH total from 3 test transfers of 0.0001 WETH each.

Bridge Flow

1. Ethereum (Sepolia): User approves Gateway → User calls sendToken on Gateway → Gateway locks WETH and emits OutboundMessageAccepted event
2. Relayers: Pick up event and relay to Bridge Hub on Polkadot (~30 minutes)
3. Bridge Hub: Verifies Ethereum consensus proof
4. Polkadot Hub Paseo: Mints wrapped WETH as foreign asset to destination account