Add Soroban smart contract interaction panel

[MJ-RWA]

Complexity: High — 200 pts

Summary

Soroban is Stellar's smart contract platform. StellarFlow has no way to interact with deployed Soroban contracts. This issue adds a developer-focused "Contract" panel where users can enter a contract ID, simulate read-only calls, and invoke write functions using Freighter signing.

Files to Create/Modify

• Create: src/lib/soroban.ts
• Create: src/pages/ContractPage.tsx
• Modify: src/App.tsx — add /contract route

Implementation Notes

soroban.ts

Use StellarSdk.SorobanRpc.Server('https://soroban-testnet.stellar.org').

export async function simulateContractCall(contractId, method, args: StellarSdk.xdr.ScVal[], sourceAddress)
export async function buildContractTx(contractId, method, args: StellarSdk.xdr.ScVal[], sourceAddress): Promise<string>

simulateContractCall builds a tx via contract.call(method, ...args) and calls rpc.simulateTransaction(tx). buildContractTx simulates first (throw on isSimulationError), then StellarSdk.SorobanRpc.assembleTransaction(tx, simResult).build().toXDR().

ContractPage layout

Contract ID: [input] [Load]
Methods:
 • balance(address) [Simulate]
 • transfer(to, amount) [Invoke]
Arguments: [JSON input]
Result: { "balance": "1000" }

• Arguments entered as JSON, converted via StellarSdk.nativeToScVal
• Simulate shows result with no signing required
• Invoke builds tx → signs with Freighter → submits via RPC → shows result

Acceptance Criteria

• Contract loads by entering a valid Soroban Contract ID
• Read-only methods simulated and result shown without Freighter
• Write methods assemble tx with resource fee, sign with Freighter, submit
• JSON argument input parsed to correct ScVal types via nativeToScVal
• Simulation errors shown clearly in the result panel
• Works on Stellar testnet (Soroban)
• Result rendered as formatted JSON

Screen Recording Requirements (with a known Soroban testnet token contract)

1. Enter contract ID → methods listed
2. Simulate balance(address) → result shown without signing
3. Invoke transfer(to, amount) → Freighter popup → execute → result shown
4. Show the tx on Stellar Expert confirming the Soroban invocation