Phase 9 Wave 1: add ReleaseMedium discriminator + Session/Mix metadata

Add ReleaseMedium enum (Cut/Session/Mix) and two 1:1 satellite entities
(SessionMetadata, MixMetadata) with EF configs and an additive migration.
ReleaseDto.ReleaseType is now nullable, nulled for non-Cut at the converter.
Existing releases default to Cut via column default; no data migration.

DeepDrftData/Data/Configurations/MixMetadataConfiguration.cs

@@ -0,0 +1,48 @@
+using Data.Data.Configurations;
+using DeepDrftModels.Entities;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+
+namespace DeepDrftData.Data.Configurations;
+
+public class MixMetadataConfiguration : BaseEntityConfiguration<MixMetadata>
+{
+    public override void Configure(EntityTypeBuilder<MixMetadata> builder)
+    {
+        // Wires up Id PK + audit columns (CreatedAt, UpdatedAt, IsDeleted) and the IsDeleted index.
+        base.Configure(builder);
+
+        builder.ToTable("mix_metadata");
+
+        // Map the base audit columns to the snake_case naming the rest of the schema uses.
+        builder.Property(e => e.Id).HasColumnName("id");
+        builder.Property(e => e.CreatedAt).HasColumnName("created_at");
+        builder.Property(e => e.UpdatedAt).HasColumnName("updated_at");
+        builder.Property(e => e.IsDeleted).HasColumnName("is_deleted");
+
+        builder.Property(e => e.ReleaseId)
+            .HasColumnName("release_id");
+
+        builder.Property(e => e.WaveformEntryKey)
+            .IsRequired()
+            .HasMaxLength(500)   // Consistent with ImagePath on ReleaseEntity; entry keys can carry GUIDs.
+            .HasColumnName("waveform_entry_key");
+
+        // 1:1 to the parent release. The unique FK index is the DB-level enforcement of the
+        // one-satellite-per-release cardinality. Cascade on delete: removing the release removes its
+        // medium satellite (unlike Track's SetNull — a satellite has no meaning without its release).
+        builder.HasOne(e => e.Release)
+            .WithOne(r => r.MixMetadata)
+            .HasForeignKey<MixMetadata>(e => e.ReleaseId)
+            .OnDelete(DeleteBehavior.Cascade);
+
+        builder.HasIndex(e => e.ReleaseId)
+            .IsUnique()
+            .HasDatabaseName("IX_mix_metadata_release_id");
+
+        // Names the is_deleted index explicitly. BaseEntityConfiguration.Configure already
+        // calls HasIndex(e => e.IsDeleted); this adds HasDatabaseName so EF always uses
+        // "IX_mix_metadata_is_deleted" regardless of auto-naming conventions.
+        builder.HasIndex(e => e.IsDeleted).HasDatabaseName("IX_mix_metadata_is_deleted");
+    }
+}

DeepDrftData/Data/Configurations/ReleaseConfiguration.cs

@@ -42,6 +42,18 @@ public class ReleaseConfiguration : BaseEntityConfiguration<ReleaseEntity>
             .HasMaxLength(500)
             .HasColumnName("image_path");
 
+        // ReleaseType is meaningful ONLY when Medium == Cut. It is the Cut medium's discriminator
+        // data and lives on the base table by deliberate, named exception:
+        //   A CutMetadata satellite (mirroring SessionMetadata/MixMetadata) was considered and
+        //   rejected. ReleaseType is read on every card of the /cuts browse — the highest-traffic
+        //   read in the system. Moving it to a satellite would put a join on that hot path. So it
+        //   stays here. Future media MUST NOT copy this pattern: the default is a satellite metadata
+        //   table; this is the one allowed exception, justified solely by the /cuts read volume.
+        //
+        // The "ReleaseType only for Cut" invariant is advisory — enforced at the service layer and
+        // surfaced via the nullable ReleaseDto.ReleaseType (nulled for non-Cut at the converter).
+        // It is NOT a DB check constraint by choice, not necessity: EF supports HasCheckConstraint,
+        // but the invariant is advisory and we keep the schema free of it.
         builder.Property(e => e.ReleaseType)
             .IsRequired()
             .HasConversion<string>()   // Store as readable string, not int ordinal
@@ -49,6 +61,13 @@ public class ReleaseConfiguration : BaseEntityConfiguration<ReleaseEntity>
             .HasColumnName("release_type")
             .HasDefaultValue(ReleaseType.Single);
 
+        builder.Property(e => e.Medium)
+            .IsRequired()
+            .HasConversion<string>()   // Store as readable string, not int ordinal
+            .HasMaxLength(20)
+            .HasColumnName("medium")
+            .HasDefaultValue(ReleaseMedium.Cut);   // Existing rows migrate to Cut with no data migration.
+
         builder.Property(e => e.CreatedByUserId)
             .HasColumnName("created_by_user_id");
 

DeepDrftData/Data/Configurations/SessionMetadataConfiguration.cs

@@ -0,0 +1,48 @@
+using Data.Data.Configurations;
+using DeepDrftModels.Entities;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+
+namespace DeepDrftData.Data.Configurations;
+
+public class SessionMetadataConfiguration : BaseEntityConfiguration<SessionMetadata>
+{
+    public override void Configure(EntityTypeBuilder<SessionMetadata> builder)
+    {
+        // Wires up Id PK + audit columns (CreatedAt, UpdatedAt, IsDeleted) and the IsDeleted index.
+        base.Configure(builder);
+
+        builder.ToTable("session_metadata");
+
+        // Map the base audit columns to the snake_case naming the rest of the schema uses.
+        builder.Property(e => e.Id).HasColumnName("id");
+        builder.Property(e => e.CreatedAt).HasColumnName("created_at");
+        builder.Property(e => e.UpdatedAt).HasColumnName("updated_at");
+        builder.Property(e => e.IsDeleted).HasColumnName("is_deleted");
+
+        builder.Property(e => e.ReleaseId)
+            .HasColumnName("release_id");
+
+        builder.Property(e => e.HeroImageEntryKey)
+            .IsRequired()
+            .HasMaxLength(500)   // Consistent with ImagePath on ReleaseEntity; entry keys can carry GUIDs.
+            .HasColumnName("hero_image_entry_key");
+
+        // 1:1 to the parent release. The unique FK index is the DB-level enforcement of the
+        // one-satellite-per-release cardinality. Cascade on delete: removing the release removes its
+        // medium satellite (unlike Track's SetNull — a satellite has no meaning without its release).
+        builder.HasOne(e => e.Release)
+            .WithOne(r => r.SessionMetadata)
+            .HasForeignKey<SessionMetadata>(e => e.ReleaseId)
+            .OnDelete(DeleteBehavior.Cascade);
+
+        builder.HasIndex(e => e.ReleaseId)
+            .IsUnique()
+            .HasDatabaseName("IX_session_metadata_release_id");
+
+        // Names the is_deleted index explicitly. BaseEntityConfiguration.Configure already
+        // calls HasIndex(e => e.IsDeleted); this adds HasDatabaseName so EF always uses
+        // "IX_session_metadata_is_deleted" regardless of auto-naming conventions.
+        builder.HasIndex(e => e.IsDeleted).HasDatabaseName("IX_session_metadata_is_deleted");
+    }
+}