fix: resolve XBullAdapter listener leak, computeMovingAverage, cert pinning, TOML version check

[iam-mercy]

Summary

Resolves four Wave issues in a single PR. Each fix is scoped to its target file and does not touch unrelated code.

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#840 — XBullAdapter leaks account-change listeners on reconnect

Issue: setupAccountChangeListener() overwrote this.unsubscribe without calling the previous one. After three connect() calls, three listeners were live; disconnect() removed only the last one. A post-disconnect account-change event then wrote an address back into an adapter the app believed torn down.

Fix: Drop the previous registration before installing a new one — mirroring LobstrAdapter.setupAccountChangeListener(). disconnect() needed no change; with at most one live listener its existing unsubscribe call is sufficient.

Files: src/wallets/adapters/XBullAdapter.ts, test/xbullAdapter.test.ts

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#781 — Add computeMovingAverage to fees/trend.ts

Issue: fees/trend.ts exposed no derived statistics. Callers needed a smoothed signal for fee forecasting.

Fix: Exported a pure computeMovingAverage(samples, windowSize) function that returns an SMA series of the same length, padding the first windowSize - 1 entries with NaN. Throws RangeError when windowSize < 1.

Files: src/fees/trend.ts, test/feeTrend.test.ts

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#780 — Certificate pinning for anchor HTTPS endpoints in AnchorVerifier

Issue: AnchorVerifier validated anchor metadata but did not verify TLS certificates, leaving it open to compromised DNS or rogue CAs.

Fix: Added optional pinnedCertFingerprints?: Record<string, string> to AnchorVerifierOptions. When a domain appears in the map, the SHA-256 fingerprint of its TLS certificate is retrieved and compared before the TOML is fetched. A mismatch throws CertificatePinningError (added to errors.ts) naming the domain. An injectable _fetchCertFingerprint option is provided for test isolation.

Files: src/anchors/AnchorVerifier.ts, src/errors.ts, test/anchorPinningAndVersion.test.ts

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#779 — Validate TOML schema version in StellarTomlParser

Issue: StellarTomlParser parsed stellar.toml files without checking VERSION, so a breaking schema revision would be processed silently.

Fix: Exported SUPPORTED_TOML_VERSIONS: readonly number[] = [2.0, 2.1]. After successful TOML parse (and before caching), VERSION is read; if present and not in SUPPORTED_TOML_VERSIONS, an UnsupportedTomlVersionError (added to errors.ts) is thrown naming the encountered version. Files without a VERSION field are accepted unchanged.

Files: src/anchors/StellarTomlParser.ts, src/errors.ts, test/anchorPinningAndVersion.test.ts

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Testing

All changes are covered by unit tests:

• test/xbullAdapter.test.ts — 7 tests covering single connect, repeated connect, disconnect listener counts, post-disconnect event immunity, and onAccountChange handler lifecycle.
• test/feeTrend.test.ts — 12 tests covering correct SMA values, NaN padding, edge cases (empty, single-element, windowSize > length), RangeError on invalid windowSize, and purity.
• test/anchorPinningAndVersion.test.ts — 23 tests covering SUPPORTED_TOML_VERSIONS shape, supported/unsupported/missing VERSION, cache behaviour on version error, fingerprint match/mismatch, case-insensitive comparison, timeout forwarding, CertificatePinningError and UnsupportedTomlVersionError shape.

129 tests pass. Existing test/anchorVerifier.test.ts (19 tests) continues to pass unchanged.

closes #840
closes #781
closes #780
closes #779

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