String aggregationKey = aggregationKeyFor(definition.getId());
        sendProgress(problem, aggregationKey);

        if (seenProblems.size() > thresholdForIntermediateSummary) {
            sendProblemSummaries();
        }
    }

    private static String aggregationKeyFor(InternalProblemId id) {
        return aggregationKeyFor(id.getGroup()) + ";" + id.getName();
    }