fix(sdk): Add comprehensive retry logic with exponential backoff for network failures

[Vincent6581]

Summary

Adds an intelligent retry layer for transient network failures, per issue #191. Deterministic failures are never retried.

Acceptance criteria

Criterion	Status
RetryConfig: maxRetries, baseDelayMs, maxDelayMs, backoffMultiplier	✅ + optional jitter; DEFAULT_RETRY_CONFIG in constants.ts
Retryable: network timeout, 429, Horizon 504, mempool full	✅ socket codes (ETIMEDOUT, ECONNRESET, …), HTTP 408/425/429/500/502/503/504, mempool is full / rate-limit message patterns, retryable Stellar result codes (tx_too_late, tx_bad_seq, …)
Non-retryable: invalid signature, insufficient funds, contract error	✅ also UNAUTHORIZED, INVALID_PARAMETERS, KYC/compliance, tx_bad_auth, op_*, any 4xx
Retry state events for UI feedback	✅ RetryEvent (retry / exhausted / succeeded) via onRetryEvent, or sdk.onRetry(listener)

Public API

import { withRetry, isRetryableError, classifyError, RateLimitError } from 'stellar-rwa-sdk';

const result = await withRetry(
  (attempt) => horizon.submitTransaction(tx),
  {
    config: { maxRetries: 5, baseDelayMs: 250, maxDelayMs: 20_000, backoffMultiplier: 2 },
    onRetryEvent: (e) => {
      if (e.type === 'retry') console.warn(`attempt ${e.attempt}/${e.maxAttempts} failed, retrying in ${e.delayMs}ms`);
    },
  }
);

Or via the SDK instance:

const sdk = new StellarRWASDK({ ...config, retry: { maxRetries: 5 } });
sdk.onRetry((e) => ui.showBackoff(e));
await sdk.withRetry((attempt) => sdk.marketClient.placeOrder(opts));

Design notes

• classifyError(error) returns { retryable, reason } — the reason string is handy for logs/telemetry. isRetryableError() wraps it.
• Backoff: min(maxDelayMs, baseDelayMs * multiplier^index) then ± jitter. sleep and rng are injectable so backoff timing is deterministic under test; a RateLimitError.retryAfterMs raises the floor of the next delay.
• Optional { aborted: boolean } signal stops further retries between attempts.

Incidental fix

errors.ts had a syntax error in the SUGGESTED_ACTIONS map ([ErrorCode.TX_BAD_SEQ' — stray quote) that prevented the module from compiling at all; that also masked a missing ParsedHorizonError type import. Both are fixed here since the file is being modified.

Files changed

• sdk/src/errors.ts — retry classification, backoff, withRetry, new error classes
• sdk/src/constants.ts — retry config + retryable code/pattern tables
• sdk/src/index.ts — exports; StellarRWASDK.withRetry() / .onRetry() / config.retry

Closes #191

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[Kevin737866]

@Vincent6581 cconflict