fix(core-internal): preserve error cause and support ErrorOptions in SdkError

packages/core-internal/src/errors/sdkErrors.ts

@@ -147,9 +147,15 @@ export class SdkError extends Error {
     constructor(
         public readonly code: SdkErrorCode,
         message: string,
-        public readonly data?: unknown
+        public readonly data?: unknown,
+        options?: ErrorOptions
     ) {
-        super(message);
+        const errorOptions =
+            options ??
+            (data && typeof data === 'object' && 'cause' in data && (data as { cause: unknown }).cause !== undefined
+                ? { cause: (data as { cause: unknown }).cause }
+                : undefined);
+        super(message, errorOptions);
         this.name = 'SdkError';
         stampErrorBrands(this, new.target);
     }

packages/core-internal/test/types/errorSurfacePins.test.ts

@@ -196,6 +196,23 @@ describe('SdkError', () => {
         expect(error.message).toBe('Request timed out');
     });
 
+    test('preserves error cause in Error.cause when passed via data.cause or options', () => {
+        const underlyingError = new TypeError('fetch failed: getaddrinfo ENOTFOUND host.invalid');
+
+        // When cause is passed via data object (as in classifyNetworkError)
+        const errorFromData = new SdkError(SdkErrorCode.EraNegotiationFailed, 'Version negotiation probe failed', {
+            cause: underlyingError
+        });
+        expect(errorFromData.cause).toBe(underlyingError);
+        expect(errorFromData.data).toEqual({ cause: underlyingError });
+
+        // When cause is passed via standard ErrorOptions
+        const errorFromOptions = new SdkError(SdkErrorCode.EraNegotiationFailed, 'Version negotiation probe failed', undefined, {
+            cause: underlyingError
+        });
+        expect(errorFromOptions.cause).toBe(underlyingError);
+    });
+
     test('SdkHttpError carries the HTTP status in data', () => {
         const error = new SdkHttpError(SdkErrorCode.ClientHttpFailedToOpenStream, 'Failed to open SSE stream: Not Found', {
             status: 404,