feat: add dual-host IM pressure test tool

loadtest/im-pressure/merge_test.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestRunMergeComputesArrivalAndPersistenceGate(t *testing.T) {
+	dir := t.TempDir()
+	a := AgentSummary{RunID: "run1", Scenario: "p2p", Machine: "a", ReadyConnections: 1000,
+		PublishAttempted: 10, PublishAccepted: 10, ExpectedPeer: 10, ReceivedPeer: 9,
+		RealtimeLost: 1, HistoryChecked: 10, HistoryFound: 10}
+	b := AgentSummary{RunID: "run1", Scenario: "p2p", Machine: "b", ReadyConnections: 1000,
+		PublishAttempted: 10, PublishAccepted: 10, ExpectedPeer: 10, ReceivedPeer: 10,
+		HistoryChecked: 10, HistoryFound: 9, PersistenceLost: 1}
+	aPath, bPath, reportPath := filepath.Join(dir, "a.json"), filepath.Join(dir, "b.json"), filepath.Join(dir, "report.json")
+	writeSummaryForTest(t, aPath, a)
+	writeSummaryForTest(t, bPath, b)
+	if err := runMerge(aPath, bPath, reportPath); err != nil {
+		t.Fatal(err)
+	}
+	var report CombinedReport
+	raw, err := os.ReadFile(reportPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err = json.Unmarshal(raw, &report); err != nil {
+		t.Fatal(err)
+	}
+	if report.ExpectedDeliveries != 20 || report.ReceivedDeliveries != 19 || report.ArrivalRate != 0.95 || report.LossRate != 0.05 {
+		t.Fatalf("unexpected delivery totals: %+v", report)
+	}
+	if report.Passed || report.PersistenceLost != 1 {
+		t.Fatalf("correctness gate did not fail: %+v", report)
+	}
+}
+
+func writeSummaryForTest(t *testing.T, path string, summary AgentSummary) {
+	t.Helper()
+	raw, err := json.Marshal(summary)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err = os.WriteFile(path, raw, 0o600); err != nil {
+		t.Fatal(err)
+	}
+}