feat: build full Soroban contract client service layer

[Uchechukwu-Ekezie]

Closes #14

What changed

• Added @stellar/stellar-sdk dependency and network config resolution (testnet/mainnet)
• Added typed error classes (ContractError, ContractErrorCode) with error parsing from SDK responses
• Added contract constants (contract IDs, timeouts, base fee) loaded from env vars
• Built core Soroban contract client handling the full lifecycle: build XDR, simulate, sign with Freighter, submit, poll for confirmation
• Added stream contract methods: createStream, withdrawStream, cancelStream, getStreamBalance, getStream
• Added vesting contract methods: createVestingSchedule, claimVesting, revokeVesting, getVestedOf, getVestingSchedule
• Added distributor contract methods: distribute, distributeCustom
• Added useContract React hook for loading/error state management
• Wired real contract calls into create stream, stream detail, and vesting pages (replacing fake setTimeout/toast handlers)
• Added vitest unit tests for error classes, error parsing, network config, and constants

Why

Every on-chain button in the app was faked with setTimeout and toast-only handlers. This adds a proper contract service layer that handles the full Soroban transaction lifecycle, enabling real on-chain interactions.

How to test

1. npm install && npm run build — should compile without errors
2. npx vitest run — 18 unit tests should pass
3. Manual: connect Freighter on testnet, create a stream, verify the contract call goes through

[ijeoma270]

went through the diff — the error types and the useContract hook are clean, good call on simulating before popping up Freighter. few things that'll bite you though:

the method names in streams.ts don't match the actual contract. the rust code has create, withdraw, cancel — you're calling create_stream, withdraw_stream, cancel_stream. soroban will just reject those.

createStream is passing the wrong args too. contract expects (sender, recipient, token, rate_per_second, start_time, stop_time) — six args, rate as u64. you're sending five args with a total amount as i128. also sender needs to be first since the contract uses it for auth checks.

token encoding — you're doing toScValBytes32(args.token) everywhere but the contract takes a Stellar address, not raw bytes. should be addressToScVal instead. same issue in distributor.ts.

the testnet passphrase in network.ts says December 2022 — it's actually December 2014. every signature will be invalid on testnet with that.

and buildContractTx builds a raw TransactionBuilder but doesn't attach the soroban auth data from simulation. you need assembleTransaction or prepareTransaction after simulation, otherwise the signed tx won't have the right footprint/auth entries and it'll fail on-chain.

CI build is failing too — probably related to the type mismatches from the wrong arg shapes.

the overall structure is solid though, just needs the contract details lined up with the actual rust code.

[Uchechukwu-Ekezie]

Thanks for the thorough review — all 6 points addressed:

1. Method names — create_stream → create (others were already correct)
2. createStream args — now passes (sender, recipient, token, rate_per_second, start_time, stop_time) matching the contract signature
3. Token encoding — changed from nativeToScVal(token, {type:'bytes'}) to Address.fromString(token).toScVal() in streams, vesting, and distributor
4. Testnet passphrase — fixed to Test Soro Network ; December 2014
5. Soroban tx assembly — simulateTx now calls rpc.assembleTransaction() after simulation, returning the assembled XDR for signing
6. Simulation result extraction — uses response.result.retval directly instead of manually parsing TransactionResult XDR

Also fixed SDK namespace (SorobanRpc → rpc) and account loading (loadAccount → getAccount) to match the installed SDK version.

TypeScript compiles clean, all 18 unit tests pass.

[ijeoma270]

LGTM, thanks for contributing