feat(stellar): retry + exponential backoff for Soroban RPC

[gregemax]

Summary

Implements task #2 — a shared retry primitive for all Stellar HTTP calls, wiring it into StellarSend and StellarReceive.

Changes

src/lib/stellar/retry.ts (new)

• StellarRetryExhaustedError — typed error carrying the last underlying error as .cause
• withRetry(fn, opts) — generic retry wrapper:
  • Up to 4 attempts (configurable)
  • Exponential backoff with jitter: 200 → 400 → 800 → 1600 ms ±25%
  • Retries on: HTTP 408, 429, 502, 503, 504 · TypeError (network/fetch) · SyntaxError (JSON parse — RPC returns HTML on overload)
  • Does not retry on: other 4xx · AbortError · StellarRetryExhaustedError itself
  • AbortSignal support — cancels cleanly mid-backoff
  • onRetry telemetry hook — emits { attempt, error, delayMs } on each retry (ready for PostHog)

src/lib/stellar/retry.test.ts (new)

• 16 unit tests with vitest + fake timers covering every retry/no-retry path

src/components/StellarSend.tsx

• All Horizon and Soroban fetches wrapped with withRetry
• StellarRetryExhaustedError caught → shows "Network unstable — try again." + inline Retry button

src/components/StellarReceive.tsx

• Probe fetch, paginated getEvents loop, balance fetch, and withdraw fetches all wrapped with withRetry
• Same user-facing error UI on exhaustion

Test results

✓ src/lib/stellar/retry.test.ts (16 tests) 33ms
Test Files  1 passed (1)
      Tests  16 passed (16)

Closes #2

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[truthixify]

Closing as duplicate. Issue #2 is being handled in #15 which was opened first (currently waiting on a rebase).

If #15 doesn't include the specific retry classifications you have here (your 133 lines of tests look more thorough than what's in #15), you could push them as a follow-up PR once #15 lands.

Other open Stellar Wave issues you'd be a fit for: https://github.com/wraith-protocol/demo/issues?q=is%3Aopen+label%3A%22Stellar+Wave%22

Thanks @gregemax.

[gregemax]

@truthixify i could't find any free issue to apply