perf(comms): alarms-only seed, capped buffers, at-least-once audit pull

tests/ZB.MOM.WW.ScadaBridge.Communication.Tests/Grpc/SiteStreamGrpcServerTests.cs

@@ -530,4 +530,54 @@ public class SiteStreamGrpcServerTests : TestKit
 
         Assert.True(condition(), $"Condition not met within {timeoutMs}ms");
     }
+
+    // ── WP2.3: the site-wide alarm feed gets its OWN, larger send channel ──
+
+    [Fact]
+    public void SiteAlarmStream_HasItsOwnLargerChannel_ThanTheDebugView()
+    {
+        // Sharing the Debug View's 1000-slot DropOldest channel meant an alarm burst during
+        // a WAN stall silently evicted operator-visible transitions to make room for
+        // diagnostics traffic. The two feeds are now sized independently.
+        var options = Microsoft.Extensions.Options.Options.Create(new CommunicationOptions());
+        var server = new SiteStreamGrpcServer(_subscriber, _logger, options);
+
+        Assert.Equal(1000, server.InstanceChannelCapacity);
+        Assert.Equal(20_000, server.SiteAlarmChannelCapacity);
+        Assert.True(server.SiteAlarmChannelCapacity > server.InstanceChannelCapacity);
+    }
+
+    [Fact]
+    public void ChannelCapacities_AreBoundFromOptions_AndFloorAtOne()
+    {
+        var options = Microsoft.Extensions.Options.Options.Create(new CommunicationOptions
+        {
+            GrpcInstanceStreamChannelCapacity = 42,
+            GrpcSiteAlarmStreamChannelCapacity = 4242,
+        });
+        var server = new SiteStreamGrpcServer(_subscriber, _logger, options);
+
+        Assert.Equal(42, server.InstanceChannelCapacity);
+        Assert.Equal(4242, server.SiteAlarmChannelCapacity);
+
+        // A misconfigured zero/negative capacity must not throw at channel-construction
+        // time deep inside a live RPC — it floors at one instead.
+        var degenerate = new SiteStreamGrpcServer(_subscriber, _logger,
+            Microsoft.Extensions.Options.Options.Create(new CommunicationOptions
+            {
+                GrpcInstanceStreamChannelCapacity = 0,
+                GrpcSiteAlarmStreamChannelCapacity = -5,
+            }));
+        Assert.Equal(1, degenerate.InstanceChannelCapacity);
+        Assert.Equal(1, degenerate.SiteAlarmChannelCapacity);
+    }
+
+    [Fact]
+    public void DroppedStreamEventCount_StartsAtZero()
+    {
+        // The raw counter behind scadabridge.site.stream.events_dropped — a fresh node has
+        // evicted nothing.
+        var server = CreateServer();
+        Assert.Equal(0, server.DroppedStreamEventCount);
+    }
 }