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

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");