perf(sitecallaudit): filtered IX_SiteCalls_Terminal index backs the retention purge predicate (plan R2-04 T10)

docs/plans/sql/AddSiteCallsTerminalIndex.sql

@@ -0,0 +1,21 @@
+BEGIN TRANSACTION;
+IF NOT EXISTS (
+    SELECT * FROM [__EFMigrationsHistory]
+    WHERE [MigrationId] = N'20260713142234_AddSiteCallsTerminalIndex'
+)
+BEGIN
+    EXEC(N'CREATE INDEX [IX_SiteCalls_Terminal] ON [SiteCalls] ([TerminalAtUtc]) WHERE [TerminalAtUtc] IS NOT NULL');
+END;
+
+IF NOT EXISTS (
+    SELECT * FROM [__EFMigrationsHistory]
+    WHERE [MigrationId] = N'20260713142234_AddSiteCallsTerminalIndex'
+)
+BEGIN
+    INSERT INTO [__EFMigrationsHistory] ([MigrationId], [ProductVersion])
+    VALUES (N'20260713142234_AddSiteCallsTerminalIndex', N'10.0.7');
+END;
+
+COMMIT;
+GO
+

src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Configurations/SiteCallEntityTypeConfiguration.cs

@@ -97,5 +97,14 @@ public class SiteCallEntityTypeConfiguration : IEntityTypeConfiguration<SiteCall
             .HasDatabaseName("IX_SiteCalls_NonTerminal")
             .HasFilter("[TerminalAtUtc] IS NULL")
             .IncludeProperties(nameof(SiteCall.SourceSite), nameof(SiteCall.SourceNode), nameof(SiteCall.Status));
+
+        // Terminal backs the daily retention purge's predicate (TerminalAtUtc IS NOT NULL
+        // AND TerminalAtUtc < cutoff) and Task 11's MIN() slice anchor: filtered to the
+        // terminal population so the purge seeks the expired tail instead of full-scanning
+        // the 365-day table (arch-review 04 round 2, R6). Complements IX_SiteCalls_NonTerminal,
+        // which is filtered to IS NULL and unusable for this predicate.
+        builder.HasIndex(s => s.TerminalAtUtc)
+            .HasDatabaseName("IX_SiteCalls_Terminal")
+            .HasFilter("[TerminalAtUtc] IS NOT NULL");
     }
 }

src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Migrations/20260713142234_AddSiteCallsTerminalIndex.cs

@@ -0,0 +1,28 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace ZB.MOM.WW.ScadaBridge.ConfigurationDatabase.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddSiteCallsTerminalIndex : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateIndex(
+                name: "IX_SiteCalls_Terminal",
+                table: "SiteCalls",
+                column: "TerminalAtUtc",
+                filter: "[TerminalAtUtc] IS NOT NULL");
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropIndex(
+                name: "IX_SiteCalls_Terminal",
+                table: "SiteCalls");
+        }
+    }
+}

src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Migrations/ScadaBridgeDbContextModelSnapshot.cs

@@ -167,6 +167,10 @@ namespace ZB.MOM.WW.ScadaBridge.ConfigurationDatabase.Migrations
 
                     SqlServerIndexBuilderExtensions.IncludeProperties(b.HasIndex("CreatedAtUtc"), new[] { "SourceSite", "SourceNode", "Status" });
 
+                    b.HasIndex("TerminalAtUtc")
+                        .HasDatabaseName("IX_SiteCalls_Terminal")
+                        .HasFilter("[TerminalAtUtc] IS NOT NULL");
+
                     b.HasIndex("SourceSite", "CreatedAtUtc")
                         .IsDescending(false, true)
                         .HasDatabaseName("IX_SiteCalls_Source_Created");

tests/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase.Tests/SchemaConfigurationTests.cs

@@ -94,6 +94,22 @@ public class SchemaConfigurationTests : IDisposable
             new[] { nameof(SiteCall.SourceSite), nameof(SiteCall.SourceNode), nameof(SiteCall.Status) },
             index.GetIncludeProperties());
     }
+
+    // arch-review 04 round 2 (R6): the daily terminal retention purge filters on
+    // TerminalAtUtc IS NOT NULL AND TerminalAtUtc < cutoff. A filtered index over the
+    // terminal population lets the purge (and Task 11's MIN() slice anchor) seek the
+    // expired tail instead of full-scanning the 365-day table. Locked shape:
+    // key = TerminalAtUtc, filter = [TerminalAtUtc] IS NOT NULL.
+    [Fact]
+    public void SiteCalls_Has_Filtered_Terminal_Index()
+    {
+        var model = _context.GetService<IDesignTimeModel>().Model;
+        var entity = model.FindEntityType(typeof(SiteCall))!;
+        var index = entity.GetIndexes().Single(i => i.GetDatabaseName() == "IX_SiteCalls_Terminal");
+
+        Assert.Equal(new[] { nameof(SiteCall.TerminalAtUtc) }, index.Properties.Select(p => p.Name).ToArray());
+        Assert.Equal("[TerminalAtUtc] IS NOT NULL", index.GetFilter());
+    }
 }
 
 public class SplitQueryBehaviourTests : IDisposable