refactor: consolidate gRPC status extraction into DatastoreException

Move extractStatus and extractGrpcStatusCode into a single shared
DatastoreException.extractGrpcStatusCode(Throwable) method that walks
the exception cause chain. Both call sites in DatastoreImpl now delegate
to this shared method.

Author: lqiu96

java-datastore/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreException.java

@@ -160,4 +160,27 @@ static DatastoreException throwInvalidRequest(String massage, Object... params)
   static DatastoreException propagateUserException(Exception ex) {
     throw new DatastoreException(BaseServiceException.UNKNOWN_CODE, ex.getMessage(), null, ex);
   }
+
+  /**
+   * Extracts the gRPC status code name from the given throwable. Walks the exception cause chain
+   * looking for a {@link DatastoreException} that carries a gRPC reason string (e.g. "ABORTED",
+   * "UNAVAILABLE"). Falls back to {@link io.grpc.Status.Code#UNKNOWN} if the status cannot be
+   * determined.
+   *
+   * @param throwable the throwable to extract the gRPC status code from
+   * @return the gRPC status code name, or "UNKNOWN" if not determinable
+   */
+  static String extractGrpcStatusCode(Throwable throwable) {
+    Throwable current = throwable;
+    while (current != null) {
+      if (current instanceof DatastoreException) {
+        String reason = ((DatastoreException) current).getReason();
+        if (reason != null && !reason.isEmpty()) {
+          return reason;
+        }
+      }
+      current = current.getCause();
+    }
+    return io.grpc.Status.Code.UNKNOWN.toString();
+  }
 }

java-datastore/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreImpl.java

@@ -37,6 +37,7 @@
 import static com.google.cloud.datastore.telemetry.TraceUtil.SPAN_NAME_TRANSACTION_RUN_QUERY;
 
 import com.google.api.core.BetaApi;
+import com.google.api.gax.grpc.GrpcStatusCode;
 import com.google.api.gax.retrying.RetrySettings;
 import com.google.cloud.BaseService;
 import com.google.cloud.ExceptionHandler;
@@ -64,6 +65,7 @@
 import com.google.datastore.v1.RunQueryResponse;
 import com.google.datastore.v1.TransactionOptions;
 import com.google.protobuf.ByteString;
+import io.grpc.Status;
 import io.opentelemetry.context.Context;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -214,11 +216,11 @@ public T call() throws DatastoreException {
         transaction = datastore.newTransaction(options);
         T value = callable.run(transaction);
         transaction.commit();
-        recordAttempt("OK");
+        recordAttempt(Status.Code.OK.toString());
         return value;
       } catch (Exception ex) {
         transaction.rollback();
-        recordAttempt(extractStatus(ex));
+        recordAttempt(DatastoreException.extractGrpcStatusCode(ex));
         throw DatastoreException.propagateUserException(ex);
       } finally {
         if (transaction.isActive()) {