fix: default gateway callback batching off

gateway/cmd/gateway/main.go

@@ -95,7 +95,7 @@ func main() {
 			resultOutbox.Consumer = getenv("GATEWAY_SUBMIT_RESULT_CONSUMER", "gateway-1")
 			resultOutbox.APIBaseURL = callbackBaseURL
 			resultOutbox.Concurrency = positiveEnvInt("GATEWAY_SUBMIT_RESULT_WORKER_CONCURRENCY", 8)
-			resultOutbox.BatchEnabled = os.Getenv("GATEWAY_CALLBACK_BATCH_ENABLED") != "false"
+			resultOutbox.BatchEnabled = enabledEnv("GATEWAY_CALLBACK_BATCH_ENABLED")
 			resultOutbox.BatchSize = positiveEnvInt("GATEWAY_CALLBACK_BATCH_SIZE", 50)
 			resultOutbox.BatchWait = time.Duration(positiveEnvInt("GATEWAY_CALLBACK_BATCH_WAIT_MS", 10)) * time.Millisecond
 			resultOutbox.GatewayInstanceID = gatewayInstanceID
@@ -234,6 +234,10 @@ func positiveEnvInt(key string, fallback int) int {
 	return value
 }
 
+func enabledEnv(key string) bool {
+	return os.Getenv(key) == "true"
+}
+
 func hostname() string {
 	name, err := os.Hostname()
 	if err != nil || name == "" {

gateway/cmd/gateway/main_test.go

@@ -0,0 +1,23 @@
+package main
+
+import "testing"
+
+func TestEnabledEnvRequiresExplicitTrue(t *testing.T) {
+	for _, testCase := range []struct {
+		name  string
+		value string
+		want  bool
+	}{
+		{name: "unset", want: false},
+		{name: "false", value: "false", want: false},
+		{name: "other value", value: "TRUE", want: false},
+		{name: "true", value: "true", want: true},
+	} {
+		t.Run(testCase.name, func(t *testing.T) {
+			t.Setenv("GATEWAY_CALLBACK_BATCH_ENABLED", testCase.value)
+			if got := enabledEnv("GATEWAY_CALLBACK_BATCH_ENABLED"); got != testCase.want {
+				t.Fatalf("enabledEnv() = %v, want %v", got, testCase.want)
+			}
+		})
+	}
+}