Add generation harness runtime

backend/app/services/harness/artifacts.py

@@ -0,0 +1,37 @@
+"""Artifact result types for generation harness workflows."""
+
+from dataclasses import dataclass
+from typing import Literal
+
+from app.services.story_status import StoryAssetStatus
+
+AssetCompletionKind = Literal["cover_image", "storybook_images", "audio"]
+
+
+@dataclass(frozen=True)
+class AssetCompletionResult:
+    """Service-level result for a generated asset completion attempt."""
+
+    asset: AssetCompletionKind
+    status: StoryAssetStatus
+    value: str | bytes | None = None
+    error: str | None = None
+    blocks_main_result: bool = False
+
+    @property
+    def succeeded(self) -> bool:
+        """Whether the asset reached a usable ready state."""
+
+        return self.status == StoryAssetStatus.READY and self.error is None
+
+
+def asset_result_metadata(result: AssetCompletionResult) -> dict:
+    """Build JSON-safe metadata for asset workflow events."""
+
+    return {
+        "asset": result.asset,
+        "status": result.status.value,
+        "error": result.error,
+        "blocks_main_result": result.blocks_main_result,
+    }
+