Add EF Core-backed failure group queries

Implements the read side of IGroupsDataStore for the SQL Server and PostgreSQL persisters. Groups are aggregated on the fly by joining FailedMessageGroups to FailedMessages and grouping by (GroupId, Title, Type)

Author: johnsimons

src/ServiceControl.Persistence.EFCore.PostgreSql/Migrations/20260731043221_AddFailureGroupClassifierIndex.Designer.cs

@@ -0,0 +1,27 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace ServiceControl.Persistence.EFCore.PostgreSql.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddFailureGroupClassifierIndex : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateIndex(
+                name: "ix_failed_message_groups_type_group_id",
+                table: "failed_message_groups",
+                columns: new[] { "type", "group_id" });
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropIndex(
+                name: "ix_failed_message_groups_type_group_id",
+                table: "failed_message_groups");
+        }
+    }
+}

src/ServiceControl.Persistence.EFCore.PostgreSql/Migrations/20260731043221_AddFailureGroupClassifierIndex.cs

@@ -305,6 +305,9 @@ protected override void BuildModel(ModelBuilder modelBuilder)
                     b.HasIndex("GroupId")
                         .HasDatabaseName("ix_failed_message_groups_group_id");
 
+                    b.HasIndex("Type", "GroupId")
+                        .HasDatabaseName("ix_failed_message_groups_type_group_id");
+
                     b.ToTable("failed_message_groups", (string)null);
                 });
 

src/ServiceControl.Persistence.EFCore.PostgreSql/Migrations/PostgreSqlServiceControlDbContextModelSnapshot.cs

@@ -0,0 +1,27 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace ServiceControl.Persistence.EFCore.SqlServer.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddFailureGroupClassifierIndex : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateIndex(
+                name: "IX_FailedMessageGroups_Type_GroupId",
+                table: "FailedMessageGroups",
+                columns: new[] { "Type", "GroupId" });
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropIndex(
+                name: "IX_FailedMessageGroups_Type_GroupId",
+                table: "FailedMessageGroups");
+        }
+    }
+}

src/ServiceControl.Persistence.EFCore.SqlServer/Migrations/20260731043129_AddFailureGroupClassifierIndex.Designer.cs

@@ -243,6 +243,8 @@ protected override void BuildModel(ModelBuilder modelBuilder)
 
                     b.HasIndex("GroupId");
 
+                    b.HasIndex("Type", "GroupId");
+
                     b.ToTable("FailedMessageGroups");
                 });
 

src/ServiceControl.Persistence.EFCore.SqlServer/Migrations/20260731043129_AddFailureGroupClassifierIndex.cs

@@ -17,6 +17,9 @@ public void Configure(EntityTypeBuilder<FailedMessageGroupEntity> builder)
 
         builder.HasIndex(e => e.GroupId);
 
+        // Drives the per-classifier group aggregate, which filters on Type and groups by GroupId.
+        builder.HasIndex(e => new { e.Type, e.GroupId });
+
         builder.HasOne<FailedMessageEntity>()
             .WithMany()
             .HasForeignKey(e => e.FailedMessageUniqueId)