SDK Integration Smoke Test Harness

[Kingsman-99]

Description

The SDK lacks an end-to-end smoke test suite that exercises the full happy-path flow — create invoice, preflight check, submit payment, verify receipt, check finality — against Stellar testnet using real Horizon calls and funded test accounts. Without this harness, regressions in Horizon API compatibility, @stellar/stellar-sdk upgrades, or cross-module integration are only caught in production. A smoke test harness should run this flow as a CI-gated integration test.

Technical Context

Add tests/integration/smokeTest.ts. Uses @stellar/stellar-sdk Keypair.random() and the testnet faucet endpoint (https://friendbot.stellar.org) to fund test accounts. Calls StellarSplitClient from src/client.ts with a testnet config. Invokes createInvoice(), preflightCheck(), submitPayment(), getReceipt(), and FinalityChecker.check(). Asserts each step returns the expected typed result. Controlled by STELLAR_TESTNET_SMOKE=1 environment variable to avoid running on every unit test pass.

Acceptance Criteria

• Smoke test funds two Keypair accounts (payer and recipient) via friendbot and creates a 2-recipient invoice with a 60/40 split
• Calls StellarSplitClient.preflightCheck() and asserts all preflight checks pass before submission
• Submits the payment and waits for finality via FinalityChecker.check() with minConfirmations: 2
• Asserts PaymentReceipt.status === 'finalized' and effectSummary reflects the correct balance deltas for both recipients
• Test is skipped when STELLAR_TESTNET_SMOKE is not set and is explicitly tagged as @integration to exclude from the default npm test run
• All CI checks (npm test, npm run build, ESLint/TypeScript) pass and the branch has no merge conflicts

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