Problem

When a transaction is aborted by the server (e.g. due to XACT_ABORT or a deadlock), subsequent commit() or rollback() calls return a TransactionError with code EABORT. However, originalError was always undefined on these errors because the error was constructed with a string message rather than an Error object.

This made it difficult for consumers to understand why the transaction was aborted without correlating errors manually.

Closes #1716

Solution

1. Capture the actual request error — When a request completes with an error and the transaction has been aborted, the error is stored as _abortReason on the transaction. This is done in the tedious request completion handlers (_query, _execute, _bulk).

2. Generic fallback — The tedious _abort handler (fired by the rollbackTransaction event) sets a generic "Transaction was rolled back by the server" fallback reason for edge cases where the specific error cannot be captured (e.g. connection-level errors).

3. Attach as originalError — A new _createAbortError() helper on the base Transaction class constructs the EABORT TransactionError and attaches _abortReason as originalError using Object.defineProperty (matching the pattern used elsewhere in MSSQLError).

Changes

• lib/base/transaction.js — Added _abortReason tracking, _createAbortError() helper, reset on _begin()
• lib/tedious/transaction.js — Generic fallback _abortReason in _abort handler
• lib/tedious/request.js — Capture actual request error as abort reason in _query, _execute, _bulk completion paths
• test/common/unit.js — 4 new unit tests for EABORT originalError behavior

Example

const tx = pool.transaction()
await tx.begin()
try {
  // This query triggers XACT_ABORT
  await tx.request().query("INSERT INTO ...")
} catch (requestErr) {
  // requestErr is the original SQL error
}
try {
  await tx.rollback()
} catch (abortErr) {
  // abortErr.code === "EABORT"
  // abortErr.originalError === requestErr  ← previously undefined
}