[BUG] TxAggregator.execute() leaks reserved nonces on failed/timed-out submissions, permanently desyncing the account's sequence cache

[N-thnI]

Priority: High

Description

TxAggregator.execute() never releases the nonce reserved in build() when submission fails before reaching the ledger — either sendTransaction returning status: "ERROR" (sequence never consumed on-chain) or the poll loop timing out. execute() doesn't even receive sourceAccountId/sequence, so there's no way for it to call nonceManager.release(...) on these paths.

Location

engine-bridge/src/tx-aggregator.ts:123-157 (execute)

Current Behavior

async execute(transaction: Transaction, opts: {...} = {}): Promise<...> {
  const sendResponse = await this.rpc.call(async (server) => server.sendTransaction(transaction));
  if (sendResponse.status === "ERROR") {
    throw new Error(`TxAggregator: sendTransaction failed with status ERROR: ...`);
  }
  while (true) {
    if (Date.now() - startTime > timeoutMs) {
      throw new Error(`TxAggregator: transaction execution timed out after ${timeoutMs}ms`);
    }
    ...

Expected Behavior

On a submission failure known not to have consumed the on-chain sequence, the reserved sequence should be released back to NonceManager.

Repro / Evidence

const nm = new NonceManager(rpc);
const aggregator = new TxAggregator(rpc, nm, new GasOracle(), Networks.TESTNET);
const batch = await aggregator.build({ ... });
await expect(aggregator.execute(batch.transaction, {...})).rejects.toThrow();
const nextSeq = await nm.reserve(signer.publicKey());
expect(nextSeq).toBe(batch.sequence); // FAILS -- nextSeq is batch.sequence + 1

Impact

Every failed/rejected/timed-out submission permanently burns a sequence number in the in-process cache without touching the chain. Under elevated error rates, the cache drifts ahead of the real account sequence until all transactions from that wallet fail with tx_bad_seq — a full outage of the fund-moving path requiring manual refresh().

Suggested Fix

Thread sourceAccountId/sequence into execute() and call nonceManager.release(...) in the ERROR and timeout catch paths.

Acceptance Criteria

• AC-1: execute() releases the sequence on sendTransaction ERROR.
• AC-2: execute() releases the sequence on poll-loop timeout.
• AC-3: New test reproducing the leak — fails on current code, passes after fix.

Definition of Done

• Fix merged with all AC items checked
• Regression test passes in CI
• No new eslint warnings