web: one line per node pair and RTT/loss on the link board

A pair of nodes now has a single line, dialed by the non-listening side or by the smaller id when both listen, so RTT is measured once. The board draws it undirected and colours it by RTT and loss; a manual setting applies to the pair.

backend/tests/MoShiro.Backend.Tests/LinkTests.cs

@@ -26,24 +26,38 @@ public sealed class LinkTests : IClassFixture<BackendFixture>
         (await _backend.GetJsonAsync(_backend.Admin, "/api/admin/links"))["items"]!.AsArray().FirstOrDefault(i => i!["dialer_id"]!.GetValue<string>() == dialer && i["listener_id"]!.GetValue<string>() == agent);
 
     [Fact]
-    public async Task ListeningAgents_AutomaticallyLinkBothDirections_WithoutSelfLinks()
+    public async Task ListeningAgents_AutomaticallyShareOneLine_DialedBySmallerId()
     {
         await using AgentSimulator first = await _backend.ConnectAgentAsync();
         await using AgentSimulator second = await _backend.ConnectAgentAsync();
-        string a = first.NodeId.Value;
-        string b = second.NodeId.Value;
+        string[] ids = [.. new[] { first.NodeId.Value, second.NodeId.Value }.Order(StringComparer.Ordinal)];
+        (string a, string b) = (ids[0], ids[1]); // a 拨 b
+        AgentSimulator listener = a == first.NodeId.Value ? second : first;
+        AgentSimulator dialer = a == first.NodeId.Value ? first : second;
         Assert.True((await LinkAsync(a, b))!["linked"]!.GetValue<bool>());
-        Assert.True((await LinkAsync(b, a))!["linked"]!.GetValue<bool>());
+        Assert.Null(await LinkAsync(b, a)); // 反方向不再有一条线路
         Assert.Null(await LinkAsync(a, a));
         using HttpResponseMessage self = await SetLinkAsync(a, a, true);
         Assert.Equal(HttpStatusCode.UnprocessableEntity, self.StatusCode);
-        await first.WaitForTaskSetAsync(s => s.Peers.Any(p => p.NodeId.Value == b));
-        await second.WaitForTaskSetAsync(s => s.Peers.Any(p => p.NodeId.Value == a));
+        await listener.WaitForTaskSetAsync(s => s.Peers.Any(p => p.NodeId.Value == a));
+        await dialer.WaitForTaskSetAsync(s => s.Peers.All(p => p.NodeId.Value != b)); // 拨出的一方不放行对端拨进来
 
-        using HttpResponseMessage off = await SetLinkAsync(a, b, false);
-        off.EnsureSuccessStatusCode();
-        Assert.False((await LinkAsync(a, b))!["linked"]!.GetValue<bool>());
+        // 手动让 b 拨 a：线路换方向，仍然只有一条
+        using HttpResponseMessage swap = await SetLinkAsync(b, a, true);
+        swap.EnsureSuccessStatusCode();
+        Assert.Null(await LinkAsync(a, b));
         Assert.True((await LinkAsync(b, a))!["linked"]!.GetValue<bool>());
+        await dialer.WaitForTaskSetAsync(s => s.Peers.Any(p => p.NodeId.Value == b));
+
+        // 关掉这一对：两个方向都不连，线路按默认方向显示，手动设置对这一对生效
+        using HttpResponseMessage off = await SetLinkAsync(b, a, false);
+        off.EnsureSuccessStatusCode();
+        Assert.Null(await LinkAsync(b, a));
+        JsonNode closed = (await LinkAsync(a, b))!;
+        Assert.False(closed["linked"]!.GetValue<bool>());
+        Assert.False(closed["override"]!.GetValue<bool>());
+        await SetLinkAsync(b, a, null);
+        Assert.True((await LinkAsync(a, b))!["linked"]!.GetValue<bool>());
     }
 
     [Fact]