Expand generation harness observability

backend/app/schemas/story_schemas.py

@@ -244,6 +244,25 @@ class GenerationProviderStatsResponse(BaseModel):
     failure_reasons: list[GenerationProviderFailureReasonResponse] = Field(default_factory=list)
 
 
+class GenerationTraceBucketResponse(BaseModel):
+    """Aggregated generation trace bucket."""
+
+    name: str
+    count: int
+
+
+class GenerationTraceSummaryResponse(BaseModel):
+    """Workflow trace summary aggregated from generation job events."""
+
+    story_id: int
+    window_days: int | None = None
+    total_events: int
+    failed_events: int
+    by_step: list[GenerationTraceBucketResponse] = Field(default_factory=list)
+    by_artifact: list[GenerationTraceBucketResponse] = Field(default_factory=list)
+    failure_categories: list[GenerationTraceBucketResponse] = Field(default_factory=list)
+
+
 class GenerationProviderAnalyticsResponse(BaseModel):
     """Provider call stats aggregated across one user's generation history."""