fix(wallet): resolve balance from the configured network's Horizon

[Degentle12]

Summary

Closes #8

The wallet store fetched balances from a hardcoded Horizon testnet URL, so mainnet-configured wallets always showed a zero (or wrong-network) balance. The balance lookup now resolves the Horizon base URL from the configured network (NEXT_PUBLIC_STELLAR_NETWORK, with NEXT_PUBLIC_STELLAR_HORIZON_URL as an override), distinguishes a Horizon 404 (a brand-new account — a valid zero) from real lookup failures, and keeps the balance fresh on connect and on a 15-second interval.

The key design decision: the fetch logic lives in a new pure module (lib/stellar/balance.ts) with no app imports, so the failure semantics and network selection are unit-testable with mocked fetch responses; the store is a thin glue layer that owns the refresh lifecycle.

Why

Before this change, store/walletStore.ts hit https://horizon-testnet.stellar.org/accounts/<address> unconditionally, bypassing the repo's network-aware infrastructure (lib/stellar/config.ts HORIZON_URLS/getStellarConfig, lib/env.ts network validation). Consequences:

• With NEXT_PUBLIC_STELLAR_NETWORK=mainnet, balance lookups still went to testnet Horizon, returning 404 (rendered as '0.0000000') or an unrelated testnet balance.
• Every failure — 404 or network error — was collapsed into a silently wrong '0.0000000', so users couldn't tell an empty account from a lookup failure.
• components/Header.tsx duplicated the same hardcoded testnet fetch with its own 15s interval, so there were two competing implementations of the same bug.

What was built

File	What it contains
lib/stellar/balance.ts	New pure module: fetchNativeBalance(address, horizonUrl) and parseNativeBalance(data). Horizon 404 returns ZERO_BALANCE with no error (new account); network failures and non-404 HTTP errors return balance: null plus a human-readable error. Trailing slashes on the base URL are tolerated. No app imports, so it runs under Node's test runner.
lib/stellar/config.ts	New resolveHorizonUrl(): honors NEXT_PUBLIC_STELLAR_HORIZON_URL when set, otherwise maps NEXT_PUBLIC_STELLAR_NETWORK (testnet/mainnet/futurenet) to the module's well-known HORIZON_URLS, where the env's mainnet maps to the public network.
store/walletStore.ts	connect now fetches the balance immediately and starts a 15s refresh interval; disconnect stops the timer; new refreshBalance() action; new balanceError state field set on lookup failures (previous balance is preserved) instead of writing a fake zero.
types/index.ts	`WalletState.balanceError: string
components/Header.tsx	Removed the duplicate hardcoded testnet fetch + its own interval; the wallet store now owns balance fetching and refresh.
components/WalletDropdown.tsx	Shows "Balance unavailable" when balanceError is set, instead of rendering a silently wrong 0.00 XLM.
tests/walletBalance.test.ts	11 unit tests with mocked fetch: native balance, no native asset, 404, network error, non-404 HTTP error, trailing-slash URL handling, testnet URL resolution, mainnet URL resolution, NEXT_PUBLIC_STELLAR_HORIZON_URL override, end-to-end mainnet fetch, and parseNativeBalance fallback.
package.json	Adds "test": "node --test \"tests/**/*.test.ts\"" (Node's built-in runner, zero new dependencies).
tsconfig.json	"target": "ES2020" (was unset, defaulting to ES3) and "allowImportingTsExtensions": true (so tests can import .ts modules under Node's native TypeScript support; safe with noEmit).

The tests exercise the exact failure semantics in the acceptance criteria: a 404 is a zero, a network error is an error, and the mainnet vs testnet URL selection is asserted end to end.

Integration changes outside store/

• lib/server/adminStore.ts, lib/server/draftStore.ts, lib/server/campaignDeployer.ts — pre-existing type errors on main (12 total) that made npm run type-check and npm run build fail before any wallet change. These are the same mechanical fixes as in PR fix(env): reconcile env schema with reads and fail fast at boot #18 (issue Environment contract is drifting: lib/env.ts schema omits variables read elsewhere and assertEnv is never invoked #9): noUncheckedIndexedAccess spread guards in the stores, and a port of campaignDeployer.ts from the removed @stellar/stellar-sdk v11 SorobanRpc/scval API to the v14 rpc/nativeToScVal/xdr API (symbol map keys preserved). Included here only because the required quality gates cannot pass without them; identical content in both PRs merges cleanly regardless of order.
• tsconfig.json — target/extension settings above, required for the new tests and for the BigInt literals in campaignDeployer.ts.

No other files were modified.

Acceptance criteria coverage

• A connected wallet's balance is fetched from the Horizon URL of the configured network, not a hardcoded URL. (lib/stellar/balance.ts + resolveHorizonUrl() in lib/stellar/config.ts; verified by tests/walletBalance.test.ts — URL selection tests)
• On mainnet configuration the balance reflects the mainnet account; switching NEXT_PUBLIC_STELLAR_NETWORK changes the lookup target. (resolveHorizonUrl() maps mainnet → https://horizon.stellar.org; tests/walletBalance.test.ts — "mainnet configuration resolves the mainnet Horizon URL" and "mainnet configuration fetches from the mainnet Horizon URL")
• A brand-new account shows zero with no error; a Horizon failure surfaces as an error rather than a silently wrong balance. (fetchNativeBalance 404 → ZERO_BALANCE/no error; network/HTTP errors → error + balanceError in the store, surfaced in WalletDropdown; tests/walletBalance.test.ts — "404 from Horizon…", "network failure…", "non-404 HTTP error…")
• Balance refreshes on reconnect and at least once after connect without user action. (store/walletStore.ts — immediate fetch on connect + 15s interval, stopped on disconnect; reconnecting restarts both)
• Tests cover the fetch with mocked responses: native balance, no native asset, 404, network error, and mainnet vs testnet URL selection. (tests/walletBalance.test.ts — 11 tests, all scenarios listed)

Test plan

• npm test — 11/11 passing (11 new tests)
• npm run type-check — no errors
• npm run lint — no warnings or errors
• npm run build — succeeds

Env vars / Notes

No new environment variables. Behavior of existing variables:

• NEXT_PUBLIC_STELLAR_NETWORK — now controls the balance lookup target (testnet → https://horizon-testnet.stellar.org, mainnet → https://horizon.stellar.org, futurenet → https://horizon-futurenet.stellar.org).
• NEXT_PUBLIC_STELLAR_HORIZON_URL — optional override that wins over the network mapping when set.

Notes:

• The refresh interval (15s) matches the cadence the previous Header.tsx implementation used, now owned by the store so it survives page navigation and stops cleanly on disconnect.
• On a failed refresh, the last known balance is preserved and balanceError is set; the dropdown shows "Balance unavailable" rather than a fake zero.
• No data migrations involved.

[ibrahimmosouf-png]

LGTM