diff --git a/backend-tests/ToxiproxyAgentProvisioningIntegrationTests.cs b/backend-tests/ToxiproxyAgentProvisioningIntegrationTests.cs
index 9862405..2e14ca7 100644
--- a/backend-tests/ToxiproxyAgentProvisioningIntegrationTests.cs
+++ b/backend-tests/ToxiproxyAgentProvisioningIntegrationTests.cs
@@ -1,4 +1,5 @@
 using System.Net.Http.Json;
+using System.Text;
 using System.Text.Json;
 using System.Text.Json.Nodes;
 using DotNet.Testcontainers.Builders;
@@ -17,6 +18,23 @@ public sealed class ToxiproxyAgentProvisioningIntegrationTests
     private const ushort ToxiproxyAdminPort = 8474;
     private const ushort OpenClawProxyPort = 8666;
 
+    [Fact]
+    public void Http_fixture_preserves_json_node_request_payload()
+    {
+        var payload = ToxiproxyHttpGatewayConnector.SerializeParameters(
+            new JsonObject
+            {
+                ["name"] = "Release Analyst",
+                ["workspace"] = "/tmp/workspace-release-analyst"
+            });
+        var json = JsonNode.Parse(payload)!.AsObject();
+
+        Assert.Equal("Release Analyst", json["name"]!.GetValue<string>());
+        Assert.Equal(
+            "/tmp/workspace-release-analyst",
+            json["workspace"]!.GetValue<string>());
+    }
+
     [ToxiproxyIntegrationFact]
     [Trait("Category", "DockerIntegration")]
     [Trait("Category", "ToxiproxyIntegration")]
@@ -292,12 +310,19 @@ internal sealed class ToxiproxyHttpGatewayConnector(Uri endpoint)
                         timeoutSource.Token);
                     break;
                 case "agents.create":
+                {
                     Interlocked.Increment(ref createCalls);
-                    response = await client.PostAsJsonAsync(
+                    var body = SerializeParameters(parameters);
+                    using var content = new StringContent(
+                        body,
+                        Encoding.UTF8,
+                        "application/json");
+                    response = await client.PostAsync(
                         "/agents/create",
-                        JsonSerializer.SerializeToNode(parameters),
+                        content,
                         timeoutSource.Token);
                     break;
+                }
                 default:
                     throw new OpenClawGatewayRpcException(
                         "METHOD_NOT_FOUND",
@@ -334,5 +359,12 @@ internal sealed class ToxiproxyHttpGatewayConnector(Uri endpoint)
     public IReadOnlyList<GatewayEventEnvelope> GetRecentEvents(int limit = 100)
         => [];
 
+    internal static string SerializeParameters(object? parameters)
+        => parameters is JsonNode jsonNode
+            ? jsonNode.ToJsonString()
+            : JsonSerializer.Serialize(
+                parameters,
+                parameters?.GetType() ?? typeof(object));
+
     public void Dispose() => client.Dispose();
 }