feat(launcher): stabilize prepared content updates

src/AcDream.App/Configuration/SessionConfiguration.cs

@@ -71,6 +71,12 @@ internal sealed class SessionContentDescriptor
 
     [JsonRequired]
     public string PreparedAssetPath { get; init; } = string.Empty;
+
+    public string? PreparedAssetOverlayPath { get; init; }
+
+    public uint? PreparedAssetBaseRecipeVersion { get; init; }
+
+    public uint? PreparedAssetEffectiveRecipeVersion { get; init; }
 }
 
 internal sealed record SessionDescriptor

src/AcDream.App/Configuration/SessionConfigurationLoader.cs

@@ -83,6 +83,18 @@ internal static class SessionConfigurationLoader
             throw new SessionConfigurationException(
                 "process.content requires non-empty datDirectory and preparedAssetPath.");
         }
+
+        bool hasOverlay = !string.IsNullOrWhiteSpace(
+            content.PreparedAssetOverlayPath);
+        bool hasBaseRecipe = content.PreparedAssetBaseRecipeVersion is > 0;
+        bool hasEffectiveRecipe =
+            content.PreparedAssetEffectiveRecipeVersion is > 0;
+        if (hasOverlay != hasBaseRecipe || hasOverlay != hasEffectiveRecipe)
+        {
+            throw new SessionConfigurationException(
+                "process.content overlay path, base recipe, and effective recipe "
+                + "must be supplied together.");
+        }
     }
 
     private static void ValidateSession(SessionDescriptor session)