fix(common): preserve Error.cause in activity failures

packages/common/src/__tests__/test-failure.ts

@@ -0,0 +1,15 @@
+import test from 'ava';
+import { defaultFailureConverter } from '../converter/data-converter';
+import { defaultPayloadConverter } from '../converter/payload-converter';
+import { ensureApplicationFailure } from '../failure';
+
+test('preserves Error.cause when converting an application failure', (t) => {
+  const cause = new Error('connection terminated');
+  const error = new Error('query failed', { cause });
+
+  const applicationFailure = ensureApplicationFailure(error);
+  const failure = defaultFailureConverter.errorToFailure(applicationFailure, defaultPayloadConverter);
+
+  t.is(applicationFailure.cause, cause);
+  t.is(failure.cause?.message, cause.message);
+});

packages/common/src/failure.ts

@@ -427,6 +427,7 @@ export class WorkflowExecutionAlreadyStartedError extends TemporalFailure {
  * - `message`: `error.message` or `String(error)`
  * - `type`: `error.constructor.name` or `error.name`
  * - `stack`: `error.stack` or `''`
+ * - `cause`: `error.cause` when it is an `Error`
  */
 export function ensureApplicationFailure(error: unknown): ApplicationFailure {
   if (error instanceof ApplicationFailure) {
@@ -435,7 +436,8 @@ export function ensureApplicationFailure(error: unknown): ApplicationFailure {
 
   const message = (isRecord(error) && String(error.message)) || String(error);
   const type = (isRecord(error) && (error.constructor?.name ?? error.name)) || undefined;
-  const failure = ApplicationFailure.create({ message, type, nonRetryable: false });
+  const cause = isRecord(error) && error.cause instanceof Error ? error.cause : undefined;
+  const failure = ApplicationFailure.create({ message, type, nonRetryable: false, cause });
   failure.stack = (isRecord(error) && String(error.stack)) || '';
   return failure;
 }