Phase 0 WP-0.2–0.9: Implement Commons (types, entities, interfaces, messages, protocol, tests)

- WP-0.2: Namespace/folder skeleton (26 directories)
- WP-0.3: Shared data types (6 enums, RetryPolicy, Result<T>)
- WP-0.4: 24 domain entity POCOs across 10 domain areas
- WP-0.5: 7 repository interfaces with full CRUD signatures
- WP-0.6: IAuditService cross-cutting interface
- WP-0.7: 26 message contract records across 8 concern areas
- WP-0.8: IDataConnection protocol abstraction with batch ops
- WP-0.9: 8 architectural constraint enforcement tests
All 40 tests pass, zero warnings.

tests/ScadaLink.Commons.Tests/Messages/MessageConventionTests.cs

@@ -0,0 +1,130 @@
+using System.Reflection;
+using System.Text.Json;
+
+namespace ScadaLink.Commons.Tests.Messages;
+
+public class MessageConventionTests
+{
+    private static readonly Assembly CommonsAssembly = typeof(ScadaLink.Commons.Types.RetryPolicy).Assembly;
+
+    private static IEnumerable<Type> GetMessageTypes() =>
+        CommonsAssembly.GetTypes()
+            .Where(t => t.Namespace != null
+                        && t.Namespace.Contains(".Messages.")
+                        && !t.IsEnum
+                        && !t.IsInterface
+                        && (t.IsClass || (t.IsValueType && !t.IsPrimitive)));
+
+    [Fact]
+    public void AllMessageTypes_ShouldBeRecords()
+    {
+        foreach (var type in GetMessageTypes())
+        {
+            // Records have a compiler-generated <Clone>$ method
+            var cloneMethod = type.GetMethod("<Clone>$", BindingFlags.Public | BindingFlags.Instance);
+            Assert.True(cloneMethod != null,
+                $"{type.FullName} in Messages namespace should be a record type");
+        }
+    }
+
+    [Fact]
+    public void AllMessageTimestampProperties_ShouldBeDateTimeOffset()
+    {
+        foreach (var type in GetMessageTypes())
+        {
+            foreach (var prop in type.GetProperties())
+            {
+                if (prop.Name.Contains("Timestamp") || prop.Name == "GeneratedAt" || prop.Name == "DeployedAt")
+                {
+                    var underlyingType = Nullable.GetUnderlyingType(prop.PropertyType) ?? prop.PropertyType;
+                    Assert.True(underlyingType == typeof(DateTimeOffset),
+                        $"{type.Name}.{prop.Name} should be DateTimeOffset but is {prop.PropertyType.Name}");
+                }
+            }
+        }
+    }
+
+    [Fact]
+    public void JsonRoundTrip_DeployInstanceCommand_ShouldSucceed()
+    {
+        var msg = new ScadaLink.Commons.Messages.Deployment.DeployInstanceCommand(
+            "dep-1", "instance-1", "abc123", "{}", "admin", DateTimeOffset.UtcNow);
+
+        var json = JsonSerializer.Serialize(msg);
+        var deserialized = JsonSerializer.Deserialize<ScadaLink.Commons.Messages.Deployment.DeployInstanceCommand>(json);
+
+        Assert.NotNull(deserialized);
+        Assert.Equal(msg.DeploymentId, deserialized!.DeploymentId);
+        Assert.Equal(msg.InstanceUniqueName, deserialized.InstanceUniqueName);
+    }
+
+    [Fact]
+    public void JsonForwardCompatibility_UnknownField_ShouldDeserialize()
+    {
+        // Simulate a newer version with an extra field
+        var json = """{"DeploymentId":"dep-1","InstanceUniqueName":"inst-1","RevisionHash":"abc","FlattenedConfigurationJson":"{}","DeployedBy":"admin","Timestamp":"2025-01-01T00:00:00+00:00","NewField":"extra"}""";
+
+        var deserialized = JsonSerializer.Deserialize<ScadaLink.Commons.Messages.Deployment.DeployInstanceCommand>(json);
+
+        Assert.NotNull(deserialized);
+        Assert.Equal("dep-1", deserialized!.DeploymentId);
+    }
+
+    [Fact]
+    public void JsonBackwardCompatibility_MissingOptionalField_ShouldDeserialize()
+    {
+        // DeploymentStatusResponse has nullable ErrorMessage
+        var json = """{"DeploymentId":"dep-1","InstanceUniqueName":"inst-1","Status":2,"Timestamp":"2025-01-01T00:00:00+00:00"}""";
+
+        var deserialized = JsonSerializer.Deserialize<ScadaLink.Commons.Messages.Deployment.DeploymentStatusResponse>(json);
+
+        Assert.NotNull(deserialized);
+        Assert.Equal("dep-1", deserialized!.DeploymentId);
+        Assert.Null(deserialized.ErrorMessage);
+    }
+
+    [Fact]
+    public void JsonRoundTrip_SiteHealthReport_ShouldSucceed()
+    {
+        var msg = new ScadaLink.Commons.Messages.Health.SiteHealthReport(
+            "site-1", 1, DateTimeOffset.UtcNow,
+            new Dictionary<string, ScadaLink.Commons.Types.Enums.ConnectionHealth>
+            {
+                ["conn1"] = ScadaLink.Commons.Types.Enums.ConnectionHealth.Connected
+            },
+            new Dictionary<string, ScadaLink.Commons.Messages.Health.TagResolutionStatus>
+            {
+                ["conn1"] = new(10, 8)
+            },
+            0, 0,
+            new Dictionary<string, int> { ["queue1"] = 5 },
+            0);
+
+        var json = JsonSerializer.Serialize(msg);
+        var deserialized = JsonSerializer.Deserialize<ScadaLink.Commons.Messages.Health.SiteHealthReport>(json);
+
+        Assert.NotNull(deserialized);
+        Assert.Equal("site-1", deserialized!.SiteId);
+        Assert.Equal(1, deserialized.SequenceNumber);
+    }
+
+    [Fact]
+    public void JsonRoundTrip_DeployArtifactsCommand_ShouldSucceed()
+    {
+        var msg = new ScadaLink.Commons.Messages.Artifacts.DeployArtifactsCommand(
+            "dep-1",
+            new List<ScadaLink.Commons.Messages.Artifacts.SharedScriptArtifact>
+            {
+                new("script1", "code", null, null)
+            },
+            null, null, null,
+            DateTimeOffset.UtcNow);
+
+        var json = JsonSerializer.Serialize(msg);
+        var deserialized = JsonSerializer.Deserialize<ScadaLink.Commons.Messages.Artifacts.DeployArtifactsCommand>(json);
+
+        Assert.NotNull(deserialized);
+        Assert.Equal("dep-1", deserialized!.DeploymentId);
+        Assert.Single(deserialized.SharedScripts!);
+    }
+}