feat(seeder): serve the demo writer's values over OPC UA

AGENTS.md

@@ -88,9 +88,10 @@ dotnet run --project SemiPlot/SemiPlot.Tools.ArchiveSeeder/SemiPlot.Tools.Archiv
   --config-dir SemiPlot\Artifacts\dev-config
 ```
 
-The demo writer is the same seeder run with `--follow <seconds>` instead of `--end`: it appends to
-the archive `converge` created and thins it into the coarse layers on every tick
-(`docs/architecture/bench.md#the-demo-writer`).
+The demo writer is the same seeder run with `--follow <seconds> --opc-port <port>` instead of `--end`:
+it appends to the archive `converge` created and thins it into the coarse layers on every tick
+(`docs/architecture/bench.md#the-demo-writer`), and serves every value over OPC UA on the port
+`--opc-port` names (`docs/architecture/bench.md#the-opc-ua-demo-server`).
 
 `SemiPlot.AppHost` runs the whole demo stand — the bench container, `converge`, the demo writer and
 the viewer — in dependency order and stops the processes it launched together; a window the viewer starts
@@ -114,7 +115,7 @@ Two projects, split on one axis: crosses a machine boundary (a socket or a conta
 | Project | Framework | References | Holds |
 | --- | --- | --- | --- |
 | `SemiPlot.Tests.Unit` | xunit v3 + `Avalonia.Headless.XUnit` | `SemiPlot.UI`, `SemiPlot.Core`, `SemiPlot.DataSource.Postgres`, `SemiPlot.Tools.ArchiveSeeder` | Every test that opens no socket and starts no container: the UI, the Core models, the seeder's generators and the provider's pure classes |
-| `SemiPlot.Tests.Integration` | xunit v3 + `Avalonia.Headless.XUnit` | the same four | The container harness, the container tests and the journeys in one xunit collection, and the socket tests that need no server |
+| `SemiPlot.Tests.Integration` | xunit v3 + `Avalonia.Headless.XUnit` | the same four | The container harness, the container tests and the journeys in one xunit collection, the OPC UA demo server's tests in `DemoScadaCollection`, and the socket tests that need no server |
 
 - Each project carries its own `TestAppBuilder.cs` with `[assembly: AvaloniaTestApplication]`. Pure
   logic uses plain `[Fact]`; tests touching ReactiveUI/ScottPlot/Avalonia use
@@ -190,11 +191,13 @@ Frame cost during a drag is measured, not asserted: `docs/architecture/testing-s
 Every test of the `ArchiveDatabaseCollection` in `SemiPlot.Tests.Integration` needs a container runtime and
 nothing else. The socket classes (`RealtimePollTests`, `CatalogueReadUnreachableTests`,
 `RealtimeSubscriptionDisposalTests`, `ConvergeReadinessTests`) carry no collection, take no fixture and run without a runtime.
+The OPC UA demo server's classes under `DemoScada/` run in `DemoScadaCollection`, which carries no
+fixture, and need no runtime either.
 `SemiPlot/bench/Dockerfile` copies `/semibase` out of
 `ghcr.io/semiteq/semibase:latest`, which the fixture pulls ahead of the build, and runs
 `semibase bench` from `/docker-entrypoint-initdb.d/` before the published port opens. The container
 carries fixed dummy passwords of the fixture's own, and the base image is the constant
-`postgres:17-alpine`. A missing runtime fails every test of the collection with
+`postgres:17-alpine`. A missing runtime fails every test of `ArchiveDatabaseCollection` with
 `TestPipelineException`; nothing skips.
 
 A run leaves nothing behind but the images it pulled: the resource reaper removes the built image,

SemiPlot/Directory.Packages.props

@@ -16,14 +16,17 @@
     <PackageVersion Include="AwesomeAssertions" Version="9.4.0"/>
     <PackageVersion Include="FluentResults" Version="4.0.0"/>
     <PackageVersion Include="Microsoft.CodeAnalysis.ResxSourceGenerator" Version="3.12.0-beta1.25218.8"/>
-    <PackageVersion Include="Microsoft.Extensions.DependencyInjection" Version="10.0.8"/>
-    <PackageVersion Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="10.0.8"/>
+    <PackageVersion Include="Microsoft.Extensions.DependencyInjection" Version="10.0.12"/>
+    <PackageVersion Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="10.0.12"/>
     <PackageVersion Include="Microsoft.Extensions.Diagnostics.Testing" Version="10.6.0"/>
-    <PackageVersion Include="Microsoft.Extensions.Logging" Version="10.0.8"/>
-    <PackageVersion Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.8"/>
+    <PackageVersion Include="Microsoft.Extensions.Logging" Version="10.0.12"/>
+    <PackageVersion Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.12"/>
+    <PackageVersion Include="Microsoft.Extensions.Logging.Console" Version="10.0.12"/>
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.6.0"/>
     <PackageVersion Include="Microsoft.Reactive.Testing" Version="6.1.0"/>
     <PackageVersion Include="Npgsql" Version="10.0.3"/>
+    <PackageVersion Include="OPCFoundation.NetStandard.Opc.Ua.Client" Version="2.0.1"/>
+    <PackageVersion Include="OPCFoundation.NetStandard.Opc.Ua.Server" Version="2.0.1"/>
     <PackageVersion Include="ReactiveUI.Avalonia" Version="12.0.3"/>
     <PackageVersion Include="ScottPlot.Avalonia" Version="5.1.59"/>
     <PackageVersion Include="Semi.Avalonia" Version="12.0.3"/>

SemiPlot/SemiPlot.AppHost/AppHost.cs

@@ -19,6 +19,8 @@
 const ushort ContainerPort = 5432;
 // One density for the seeded day and the live tail, so the chart shows no seam between them.
 const string ChangeSeconds = "0.5";
+// A running Simple-Scada holds 49875, so the stand serves OPC UA on a port of its own.
+const string OpcPort = "55875";
 
 // AppHostDirectory is SemiPlot/SemiPlot.AppHost, so the tracked set sits two levels above it.
 var trackedConfiguration = Path.GetFullPath(Path.Combine(builder.AppHostDirectory, "..", "..", "ConfigFiles"));
@@ -48,7 +50,11 @@
 	.WaitFor(bench);
 
 builder.AddProject<Projects.SemiPlot_Tools_ArchiveSeeder>("writer")
-	.WithArgs("--connection", writerConnection, "--follow", "1", "--change-seconds", ChangeSeconds)
+	.WithArgs(
+		"--connection", writerConnection,
+		"--follow", "1",
+		"--change-seconds", ChangeSeconds,
+		"--opc-port", OpcPort)
 	.WaitForCompletion(converge);
 
 builder.AddProject<Projects.SemiPlot_UI>("viewer")

SemiPlot/SemiPlot.Tests.Integration/CoarseFlushTests.cs

@@ -248,7 +248,9 @@ private FollowOptions Options()
 			TimeSpan.FromSeconds(1),
 			PenCount,
 			SeederOptions.DefaultSeed,
-			SeederOptions.DefaultChangeSeconds);
+			SeederOptions.DefaultChangeSeconds,
+			TimeSpan.Zero,
+			55875);
 	}
 
 	// What LayerThinner selects for one period, in the order the read returns.

SemiPlot/SemiPlot.Tests.Integration/DemoScada/DemoScadaCollection.cs

@@ -0,0 +1,10 @@
+using Xunit;
+
+namespace SemiPlot.Tests.Integration.DemoScada;
+
+// Every demo-server test joins this collection so no two servers start side by side.
+[CollectionDefinition(Name)]
+public sealed class DemoScadaCollection
+{
+	public const string Name = "demo-scada";
+}

SemiPlot/SemiPlot.Tests.Integration/DemoScada/DemoScadaHost.cs

@@ -0,0 +1,114 @@
+using System.Net;
+using System.Net.Sockets;
+
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Testing;
+
+using Opc.Ua;
+
+using SemiPlot.Tools.ArchiveSeeder;
+
+namespace SemiPlot.Tests.Integration.DemoScada;
+
+/// <summary>Starts demo servers over one temporary certificate directory and one log collector.</summary>
+public sealed class DemoScadaHost : IDisposable
+{
+	private const int StartAttempts = 3;
+
+	// 4840 is where the stack binds when asked for port 0, and 49875 is the real Simple-Scada's port.
+	private static readonly int[] _reservedPorts = [4840, 49875];
+
+	private readonly ILoggerFactory _loggerFactory;
+
+	public DemoScadaHost()
+	{
+		CertificateDirectory = Path.Combine(
+			Path.GetTempPath(),
+			"SemiPlot.Tests",
+			$"DemoScada-{Guid.NewGuid():N}");
+		_loggerFactory = LoggerFactory.Create(builder => builder
+			.AddProvider(new FakeLoggerProvider(Logs))
+			.SetMinimumLevel(LogLevel.Warning));
+	}
+
+	/// <summary>The zone every test server archives in: no DST, and nine hours off a UTC test machine.</summary>
+	public static TimeZoneInfo ArchiveZone { get; } = TimeZoneInfo.FindSystemTimeZoneById("Asia/Tokyo");
+
+	/// <summary><see cref="StartAsync"/> picks the port.</summary>
+	public static FollowOptions Options { get; } = new(
+		"Host=127.0.0.1;Database=unused",
+		TimeSpan.FromSeconds(1),
+		PenCount: 8,
+		Seed: 1,
+		ChangeSeconds: 0.5,
+		ArchiveLag: TimeSpan.Zero,
+		OpcPort: 0);
+
+	public string CertificateDirectory { get; }
+
+	public FakeLogCollector Logs { get; } = new();
+
+	/// <summary>Starts a server on a free loopback port, retrying when another process takes the port first.</summary>
+	public async Task<DemoScadaServer> StartAsync(FollowOptions options)
+	{
+		for (var attempt = 1; ; attempt++)
+		{
+			try
+			{
+				return await StartOnPortAsync(options with { OpcPort = FreePort() });
+			}
+			catch (SeederException exception) when (attempt < StartAttempts && IsBusyPort(exception))
+			{
+			}
+		}
+	}
+
+	private static bool IsBusyPort(SeederException exception)
+	{
+		return exception.InnerException is ServiceResultException listener
+			&& listener.StatusCode == StatusCodes.BadNoCommunication;
+	}
+
+	public Task<DemoScadaServer> StartOnPortAsync(FollowOptions options)
+	{
+		return DemoScadaServer.StartAsync(options, ArchiveZone, CertificateDirectory, _loggerFactory);
+	}
+
+	public static int FreePort()
+	{
+		while (true)
+		{
+			var listener = new TcpListener(IPAddress.Loopback, 0);
+			listener.Start();
+			var port = ((IPEndPoint)listener.LocalEndpoint).Port;
+			listener.Stop();
+
+			if (!_reservedPorts.Contains(port))
+			{
+				return port;
+			}
+		}
+	}
+
+	/// <summary>The server's records at Warning and above so far, for an assertion's reason.</summary>
+	public string ServerLog()
+	{
+		var records = Logs.GetSnapshot();
+
+		return records.Count == 0
+			? "the server logged nothing at Warning or above"
+			: "the server logged " + string.Join(
+				Environment.NewLine,
+				records.Select(record => $"{record.Level} {record.Category}: {record.Message} {record.Exception}"));
+	}
+
+	public void Dispose()
+	{
+		_loggerFactory.Dispose();
+
+		if (Directory.Exists(CertificateDirectory))
+		{
+			Directory.Delete(CertificateDirectory, recursive: true);
+		}
+	}
+}