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/Entities/EntityConventionTests.cs

@@ -0,0 +1,89 @@
+using System.Collections;
+using System.Reflection;
+
+namespace ScadaLink.Commons.Tests.Entities;
+
+public class EntityConventionTests
+{
+    private static readonly Assembly CommonsAssembly = typeof(ScadaLink.Commons.Types.RetryPolicy).Assembly;
+
+    private static IEnumerable<Type> GetEntityTypes() =>
+        CommonsAssembly.GetTypes()
+            .Where(t => t.IsClass && !t.IsAbstract && t.Namespace != null
+                        && t.Namespace.Contains(".Entities."));
+
+    [Fact]
+    public void AllEntities_ShouldHaveNoEfAttributes()
+    {
+        var efAttributeNames = new HashSet<string>
+        {
+            "KeyAttribute", "ForeignKeyAttribute", "TableAttribute",
+            "ColumnAttribute", "RequiredAttribute", "MaxLengthAttribute",
+            "StringLengthAttribute", "DatabaseGeneratedAttribute",
+            "NotMappedAttribute", "IndexAttribute", "InversePropertyAttribute"
+        };
+
+        foreach (var entityType in GetEntityTypes())
+        {
+            // Check class-level attributes
+            var classAttrs = entityType.GetCustomAttributes(true);
+            foreach (var attr in classAttrs)
+            {
+                Assert.DoesNotContain(attr.GetType().Name, efAttributeNames);
+            }
+
+            // Check property-level attributes
+            foreach (var prop in entityType.GetProperties())
+            {
+                var propAttrs = prop.GetCustomAttributes(true);
+                foreach (var attr in propAttrs)
+                {
+                    Assert.False(efAttributeNames.Contains(attr.GetType().Name),
+                        $"Entity {entityType.Name}.{prop.Name} has EF attribute {attr.GetType().Name}");
+                }
+            }
+        }
+    }
+
+    [Fact]
+    public void AllTimestampProperties_ShouldBeDateTimeOffset()
+    {
+        var timestampNames = new HashSet<string>(StringComparer.OrdinalIgnoreCase)
+        {
+            "Timestamp", "DeployedAt", "CompletedAt", "GeneratedAt",
+            "ReportTimestamp", "SnapshotTimestamp"
+        };
+
+        foreach (var entityType in GetEntityTypes())
+        {
+            foreach (var prop in entityType.GetProperties())
+            {
+                if (timestampNames.Contains(prop.Name))
+                {
+                    var underlyingType = Nullable.GetUnderlyingType(prop.PropertyType) ?? prop.PropertyType;
+                    Assert.True(underlyingType == typeof(DateTimeOffset),
+                        $"{entityType.Name}.{prop.Name} should be DateTimeOffset but is {prop.PropertyType.Name}");
+                }
+            }
+        }
+    }
+
+    [Fact]
+    public void NavigationProperties_ShouldBeICollection()
+    {
+        foreach (var entityType in GetEntityTypes())
+        {
+            foreach (var prop in entityType.GetProperties())
+            {
+                if (prop.PropertyType.IsGenericType &&
+                    typeof(IEnumerable).IsAssignableFrom(prop.PropertyType) &&
+                    prop.PropertyType != typeof(string))
+                {
+                    Assert.True(
+                        prop.PropertyType.GetGenericTypeDefinition() == typeof(ICollection<>),
+                        $"{entityType.Name}.{prop.Name} should be ICollection<T> but is {prop.PropertyType.Name}");
+                }
+            }
+        }
+    }
+}