fix(governance): fail soft owner review readbacks

apps/api/src/api/v1/ai_governance.py

@@ -341,6 +341,24 @@ async def get_km_stale_owner_reviews(
         )
     except KmStaleOwnerReviewError as exc:
         raise HTTPException(status_code=exc.status_code, detail=exc.detail) from exc
+    except Exception as exc:
+        logger.warning(
+            "km_stale_owner_reviews_readback_degraded",
+            project_id=project_id,
+            dispatch_status=dispatch_status,
+            limit=limit,
+            error_type=type(exc).__name__,
+        )
+        return KnowledgeStaleOwnerReviewInboxResponse(
+            project_id=project_id,
+            dispatch_status=dispatch_status,
+            total=0,
+            returned=0,
+            writes_on_read=False,
+            manual_review_required=True,
+            items=[],
+            generated_at=now_taipei(),
+        )
 
 
 # =============================================================================
@@ -366,10 +384,35 @@ async def get_km_stale_owner_review_burndown(
         project_id=project_id,
         limit=limit,
     )
-    return await query_km_stale_owner_review_burndown(
-        project_id=project_id,
-        limit=limit,
-    )
+    try:
+        return await query_km_stale_owner_review_burndown(
+            project_id=project_id,
+            limit=limit,
+        )
+    except Exception as exc:
+        logger.warning(
+            "km_stale_owner_review_burndown_readback_degraded",
+            project_id=project_id,
+            limit=limit,
+            error_type=type(exc).__name__,
+        )
+        return KnowledgeStaleOwnerReviewBurnDownResponse(
+            project_id=project_id,
+            burn_down_status="no_data",
+            current_snapshot=None,
+            entries_to_threshold=0,
+            pending_owner_reviews=0,
+            completed_owner_reviews=0,
+            completion_audit_total=0,
+            stale_ratio_recheck_total=0,
+            latest_stale_count_delta=None,
+            latest_stale_ratio_delta=None,
+            writes_on_read=False,
+            manual_review_required=True,
+            returned=0,
+            items=[],
+            generated_at=now_taipei(),
+        )
 
 
 # =============================================================================