[Codeinx]

Problem

There was no Soroban integration at all — no client, no transaction handling — despite that being the service's stated purpose. Public RPC endpoints are rate-limited and intermittently unavailable, so a naive implementation would be flaky in exactly the way that erodes trust in a custody-adjacent service.

What this adds

New module: src/soroban/

• Timeouts on every call, enforced by racing the call against a timer rather than relying on the callee to cooperate with an AbortSignal — so a hung transport still returns (with a timeout error) instead of blocking forever.
• Retry with exponential backoff and full jitter, bounded by maxAttempts — applied only to idempotent operations (simulate, getTransactionStatus).
• Circuit breaker (src/soroban/circuitBreaker.ts) that trips after consecutive failures and fails fast while open, instead of queuing requests behind a dead endpoint.
• Correct submission flow: submit() is never retried by the client. The only recovery path after a submit error is pollUntilConfirmed(), which polls by transaction hash — blind-retrying a submit is how double-spends happen. submitAndConfirm() chains submit → poll for callers that want the full flow.
• Typed errors: SorobanTransportError, SorobanTimeoutError, SorobanSimulationError, SorobanContractError, CircuitOpenError — so callers can branch on failure kind instead of parsing message strings.

Kept to a lightweight fetch-based JSON-RPC transport rather than pulling in the full @stellar/stellar-sdk, so this stays small and easy to mock, and the SDK's higher-level transaction builders can be layered on top later without touching the retry/timeout/circuit-breaking behavior here.

Testing

src/soroban/client.test.ts runs against a mocked RpcTransport, covering:

• a transient transport failure that succeeds on retry
• a call that hangs and is caught by the timeout
• the circuit opening after repeated failures and failing fast on the next call
• submit() never being retried internally, even on failure
• the poll-after-429 recovery path

All existing tests continue to pass; npm run lint, npm run build, npm test, and npm audit --audit-level=high are all clean on this branch.

Scope note

This PR only adds src/soroban/** (new files) — it does not touch any file shared with the other two PRs open against this issue tracker (#54, #58), so it should apply independently of merge order.

Closes #44.