fix: trace delayed websocket acknowledgements

loadtest/im-pressure/model_test.go

@@ -3,6 +3,7 @@ package main
 import (
 	"os"
 	"path/filepath"
+	"reflect"
 	"testing"
 )
 
@@ -24,6 +25,33 @@ func TestLoadConfigAppliesBoundedHistoryDefaults(t *testing.T) {
 	}
 }
 
+func TestAssignAgentEndpointsDistributesDialIPsAcrossMachines(t *testing.T) {
+	cfg := &Config{
+		Endpoints: map[string][]string{"a": {"wss://api.example.test/ws"}, "b": {"wss://api.example.test/ws"}},
+		DialIPs:   map[string][]string{"a": {"192.0.2.1", "192.0.2.2", "192.0.2.3"}, "b": {"192.0.2.1", "192.0.2.2", "192.0.2.3"}},
+	}
+	a := []AccountRecord{{Index: 1}, {Index: 2}, {Index: 3}}
+	b := []AccountRecord{{Index: 1}, {Index: 2}, {Index: 3}}
+	assignAgentEndpoints(cfg, "a", a)
+	assignAgentEndpoints(cfg, "b", b)
+	got := []string{a[0].DialIP, b[0].DialIP, a[1].DialIP, b[1].DialIP, a[2].DialIP, b[2].DialIP}
+	want := []string{"192.0.2.1", "192.0.2.2", "192.0.2.3", "192.0.2.1", "192.0.2.2", "192.0.2.3"}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("unexpected dial IP distribution: got=%v want=%v", got, want)
+	}
+}
+
+func TestLoadConfigRejectsInvalidDialIP(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "config.json")
+	raw := []byte(`{"http_base":"https://example.test","endpoints":{"a":["wss://a"],"b":["wss://b"]},"dial_ips":{"a":["not-an-ip"]}}`)
+	if err := os.WriteFile(path, raw, 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := loadConfig(path); err == nil {
+		t.Fatal("invalid dial IP was accepted")
+	}
+}
+
 func TestSingleMachineExampleUsesSixtyPercentCapacity(t *testing.T) {
 	cfg, err := loadConfig("config.single-machine.example.json")
 	if err != nil {