fix: preserve originalError on EABORT TransactionError

[dhensby]

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
}

[Copilot]

Pull request overview

This PR preserves the underlying abort cause on EABORT transaction errors so consumers can inspect originalError after server-aborted transactions.

Changes:

• Tracks _abortReason on transactions and attaches it to generated EABORT errors.
• Captures request errors in tedious request completion paths and provides a generic abort fallback.
• Adds unit coverage for base transaction abort error behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
lib/base/transaction.js	Adds abort reason tracking and EABORT error construction.
lib/tedious/transaction.js	Sets a generic server-rollback abort reason fallback.
lib/tedious/request.js	Attempts to capture request errors as transaction abort reasons.
test/common/unit.js	Adds unit tests for EABORT originalError behavior.

Comments suppressed due to low confidence (2)

lib/tedious/request.js:509

• In streaming mode error is never populated because the code only assigns it when !this.stream, so this branch cannot preserve the actual request error for an aborted streaming query. The request errors are still collected in errors for stream mode, so use the last collected error (when present) to set _abortReason before invoking the callback.

            if (error && this.parent._aborted) {
              this.parent._abortReason = error
            }

lib/tedious/request.js:876

• In streaming mode error remains undefined because it is assigned only inside the !this.stream branch, so aborted streaming executions keep only the generic fallback instead of the actual request error. Since errors is populated for stream mode too, set _abortReason from the last collected error when the transaction has been aborted.

            if (error && this.parent._aborted) {
              this.parent._abortReason = error
            }