fix: harden single-machine load handling

loadtest/im-pressure/merge.go

@@ -38,6 +38,8 @@ type CombinedReport struct {
 	OutOfOrder            int64               `json:"out_of_order"`
 	OrderingViolations    []OrderingViolation `json:"ordering_violations,omitempty"`
 	Disconnects           int64               `json:"disconnects"`
+	DisconnectReasons     map[string]int64    `json:"disconnect_reasons,omitempty"`
+	DisconnectSamples     []DisconnectSample  `json:"disconnect_samples,omitempty"`
 	UnexpectedMessages    int64               `json:"unexpected_messages"`
 	HistoryChecked        int64               `json:"history_checked"`
 	HistoryFound          int64               `json:"history_found"`
@@ -62,7 +64,7 @@ func runMerge(aPath, bPath, output string) error {
 		return fmt.Errorf("agent summaries do not belong to the same run")
 	}
 	report := CombinedReport{RunID: a.RunID, Scenario: a.Scenario, GeneratedAt: time.Now().UTC(), Agents: []AgentSummary{a, b}, Passed: true,
-		PublishErrors: make(map[string]int64)}
+		PublishErrors: make(map[string]int64), DisconnectReasons: make(map[string]int64)}
 	for _, summary := range report.Agents {
 		expectedConnections := summary.ExpectedConnections
 		if expectedConnections == 0 {
@@ -92,6 +94,15 @@ func runMerge(aPath, bPath, output string) error {
 		report.OutOfOrder += summary.OutOfOrder
 		report.OrderingViolations = append(report.OrderingViolations, summary.OrderingViolations...)
 		report.Disconnects += summary.Disconnects
+		for category, count := range summary.DisconnectReasons {
+			report.DisconnectReasons[category] += count
+		}
+		if remaining := 100 - len(report.DisconnectSamples); remaining > 0 {
+			if remaining > len(summary.DisconnectSamples) {
+				remaining = len(summary.DisconnectSamples)
+			}
+			report.DisconnectSamples = append(report.DisconnectSamples, summary.DisconnectSamples[:remaining]...)
+		}
 		report.UnexpectedMessages += summary.UnexpectedMessages
 		report.HistoryChecked += summary.HistoryChecked
 		report.HistoryFound += summary.HistoryFound