fix grpc: use no-OK grpc status when CompletionQueue returned ok=false on the client-side Finish

commit_hash:42188f3ad14baf8c26e2c292a60bf0a7506e3acd

Author: kpavlov00

grpc/include/userver/ugrpc/client/impl/unary_call.hpp

@@ -181,9 +181,21 @@ class UnaryCall final {
                 return std::move(status_);
 
             case ugrpc::impl::AsyncMethodInvocation::WaitStatus::kError:
-                // CompletionQueue returned ok=false.
-                // RPC has finished in abnormal manner.
-                // This could mean the response message was not received or could not be deserialized.
+                // CompletionQueue returned ok=false on the client-side Finish. grpcpp still fills
+                // `status_` from the received trailers (a real server status), or from a status that
+                // grpc-core synthesized when the call failed/was cancelled (e.g. UNAVAILABLE or
+                // CANCELLED, see grpc/grpc#4972). Do not discard that grpc-core status: surface it so
+                // it is mapped to the proper exception and retried like any other gRPC status.
+                if (impl::IsRequestCancelledByDeadlinePropagation(status_, state_)) {
+                    return utils::unexpected{SpecialCaseCompletionType::kTimeoutDeadlinePropagated};
+                }
+                if (!status_.ok()) {
+                    ugrpc::impl::ClampStatusCodeToValidRange(status_);
+                    return std::move(status_);
+                }
+                // ok==false while the trailing status is OK means the response was not received or
+                // could not be deserialized: there is no valid response and no meaningful status to
+                // surface, so report a (retryable) network error.
                 return utils::unexpected{SpecialCaseCompletionType::kNetworkError};
 
             case ugrpc::impl::AsyncMethodInvocation::WaitStatus::kCancelled: