Implement FastAPI Temporal MVP pipeline

app/workers/activities/fusion_activities.py

@@ -0,0 +1,19 @@
+"""Fusion mock activity."""
+
+from temporalio import activity
+
+from app.domain.enums import AssetType
+from app.workers.activities.tryon_activities import execute_asset_step
+from app.workers.workflows.types import MockActivityResult, StepActivityInput
+
+
+@activity.defn
+async def run_fusion_activity(payload: StepActivityInput) -> MockActivityResult:
+    """Mock face and body fusion."""
+
+    return await execute_asset_step(
+        payload,
+        AssetType.FUSION,
+        extra_metadata={"face_asset_id": payload.selected_asset_id},
+    )
+