diff --git a/backend/tests/MoShiro.Backend.Tests/AgentHarness.cs b/backend/tests/MoShiro.Backend.Tests/AgentHarness.cs
index d82c0af..078d944 100644
--- a/backend/tests/MoShiro.Backend.Tests/AgentHarness.cs
+++ b/backend/tests/MoShiro.Backend.Tests/AgentHarness.cs
@@ -119,6 +119,7 @@ public sealed class AgentHarness : IAsyncDisposable
             bool enabled = kind != "connect";
             if (rateHz is { } hz && kind != "connect")
             {
+                parameters["adaptive"] = false; // 固定频率：用例按这个速率发包，限速也按它算
                 parameters["rate_hz"] = hz;
             }
 
diff --git a/backend/tests/MoShiro.Backend.Tests/AgentMeshTests.cs b/backend/tests/MoShiro.Backend.Tests/AgentMeshTests.cs
index b561aa9..87a9beb 100644
--- a/backend/tests/MoShiro.Backend.Tests/AgentMeshTests.cs
+++ b/backend/tests/MoShiro.Backend.Tests/AgentMeshTests.cs
@@ -10,18 +10,21 @@ public sealed class AgentMeshTests : IClassFixture<BackendFixture>
 
     public AgentMeshTests(BackendFixture backend) => _backend = backend;
 
+    /// <summary>两个都监听的 Agent 只有一条线路：id 较小的拨出，上下行都在这一条连接上测。</summary>
     [Fact]
-    public async Task ListeningAgents_MeasureBothDirections_AndReportThroughTheirBackendLinks()
+    public async Task ListeningAgents_ShareOneLine_DialedBySmallerId_AndReportThroughTheirBackendLinks()
     {
-        await using AgentHarness a = await AgentHarness.StartAsync(_backend);
-        await using AgentHarness b = await AgentHarness.StartAsync(_backend);
-        await a.OverrideLineTasksAsync(rateHz: 30);
-        await b.OverrideLineTasksAsync(rateHz: 30);
+        await using AgentHarness first = await AgentHarness.StartAsync(_backend);
+        await using AgentHarness second = await AgentHarness.StartAsync(_backend);
+        (AgentHarness dialer, AgentHarness listener) = string.CompareOrdinal(first.Id, second.Id) < 0 ? (first, second) : (second, first);
+        await dialer.OverrideLineTasksAsync(rateHz: 30);
+        await listener.OverrideLineTasksAsync(rateHz: 30);
         await BackendFixture.EventuallyAsync(
-            () => Task.FromResult(a.App.Dialer.IsConnected(b.Id) && b.App.Dialer.IsConnected(a.Id)),
-            TimeSpan.FromSeconds(30), "both listening agents should establish outgoing measurement sessions");
+            () => Task.FromResult(dialer.App.Dialer.IsConnected(listener.Id)),
+            TimeSpan.FromSeconds(30), "the agent with the smaller id should establish the outgoing measurement session");
+        Assert.False(listener.App.Dialer.IsConnected(dialer.Id)); // 反方向不再拨
 
-        using HttpResponseMessage retry = await _backend.Admin.PostAsync($"/api/admin/links/{a.Id}/{b.Id}/retry", null);
+        using HttpResponseMessage retry = await _backend.Admin.PostAsync($"/api/admin/links/{dialer.Id}/{listener.Id}/retry", null);
         Assert.Equal(HttpStatusCode.Accepted, retry.StatusCode);
         JsonNode result = JsonNode.Parse(await retry.Content.ReadAsStringAsync())!;
         Assert.True(result["queued"]!.GetValue<bool>());
@@ -29,18 +32,16 @@ public sealed class AgentMeshTests : IClassFixture<BackendFixture>
         await BackendFixture.EventuallyAsync(async () =>
         {
             JsonNode matrix = await _backend.GetJsonAsync(_backend.Admin, "/api/admin/links");
-            return matrix["items"]!.AsArray().Count(i =>
-                ((i!["dialer_id"]!.GetValue<string>() == a.Id && i["listener_id"]!.GetValue<string>() == b.Id)
-                || (i["dialer_id"]!.GetValue<string>() == b.Id && i["listener_id"]!.GetValue<string>() == a.Id))
-                && i["connected"]!.GetValue<bool>()) == 2;
-        }, TimeSpan.FromSeconds(30), "each agent heartbeat should report its outgoing connection");
+            JsonNode[] pair = [.. matrix["items"]!.AsArray().Select(i => i!).Where(i =>
+                (i["dialer_id"]!.GetValue<string>() == dialer.Id && i["listener_id"]!.GetValue<string>() == listener.Id)
+                || (i["dialer_id"]!.GetValue<string>() == listener.Id && i["listener_id"]!.GetValue<string>() == dialer.Id))];
+            return pair.Length == 1 && pair[0]["connected"]!.GetValue<bool>();
+        }, TimeSpan.FromSeconds(30), "the dialer's heartbeat should report its outgoing connection, and the pair should have a single line");
 
         await BackendFixture.EventuallyAsync(async () =>
         {
-            JsonNode left = await _backend.GetJsonAsync(_backend.Admin, $"/api/admin/raw/chunks?agent_id={a.Id}");
-            JsonNode right = await _backend.GetJsonAsync(_backend.Admin, $"/api/admin/raw/chunks?agent_id={b.Id}");
-            return left["items"]!.AsArray().Any(c => c!["kind"]!.GetValue<string>() == "udp_echo" && c["series"]!.GetValue<string>() == "line:" + b.Id)
-                && right["items"]!.AsArray().Any(c => c!["kind"]!.GetValue<string>() == "udp_echo" && c["series"]!.GetValue<string>() == "line:" + a.Id);
-        }, TimeSpan.FromSeconds(40), "both directed lines should persist measured packet data");
+            JsonNode chunks = await _backend.GetJsonAsync(_backend.Admin, $"/api/admin/raw/chunks?agent_id={listener.Id}");
+            return chunks["items"]!.AsArray().Any(c => c!["kind"]!.GetValue<string>() == "udp_echo" && c["series"]!.GetValue<string>() == "line:" + dialer.Id);
+        }, TimeSpan.FromSeconds(40), "the line should persist measured packet data");
     }
 }