fix(governance): fail soft work-items readbacks

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

@@ -65,6 +65,7 @@ from src.services.governance_query_service import (
     query_km_review_draft_dedupe,
     query_km_stale_candidates,
 )
+from src.utils.timezone import now_taipei
 
 logger = structlog.get_logger(__name__)
 
@@ -164,12 +165,29 @@ async def get_governance_queue(
         page=page,
         size=size,
     )
-    return await query_governance_queue(
-        dispatch_status=dispatch_status,
-        event_types=event_type,
-        page=page,
-        size=size,
-    )
+    try:
+        return await query_governance_queue(
+            dispatch_status=dispatch_status,
+            event_types=event_type,
+            page=page,
+            size=size,
+        )
+    except Exception as exc:
+        logger.warning(
+            "governance_queue_readback_degraded",
+            dispatch_status=dispatch_status,
+            event_type=event_type,
+            page=page,
+            size=size,
+            error_type=type(exc).__name__,
+        )
+        return GovernanceQueueResponse(
+            items=[],
+            total=0,
+            page=page,
+            size=size,
+            table_pending=True,
+        )
 
 
 # =============================================================================
@@ -190,7 +208,21 @@ async def get_km_review_draft_dedupe(
     owner_action，不自動 archive、不自動 approve/publish KM。
     """
     logger.debug("km_review_draft_dedupe_request", limit=limit)
-    return await query_km_review_draft_dedupe(limit=limit)
+    try:
+        return await query_km_review_draft_dedupe(limit=limit)
+    except Exception as exc:
+        logger.warning(
+            "km_review_draft_dedupe_readback_degraded",
+            limit=limit,
+            error_type=type(exc).__name__,
+        )
+        return KnowledgeReviewDraftDedupeResponse(
+            total_review_drafts=0,
+            event_group_total=0,
+            duplicate_draft_total=0,
+            groups=[],
+            generated_at=now_taipei(),
+        )
 
 
 # =============================================================================

apps/api/tests/test_ai_governance_endpoints.py

@@ -401,6 +401,25 @@ class TestQueueEndpoint:
         assert len(data["items"]) == 1
         assert data["items"][0]["dispatch_status"] == "pending"
 
+    def test_readback_exception_returns_degraded_queue(self, client):
+        """Work Items 背景讀取失敗時應 fail-soft，不讓前台收到 500."""
+        with patch(
+            "src.api.v1.ai_governance.query_governance_queue",
+            new=AsyncMock(side_effect=RuntimeError("temporary readback failure")),
+        ):
+            r = client.get(
+                "/api/v1/ai/governance/queue?dispatch_status=all"
+                "&event_type=knowledge_degradation&size=20"
+            )
+
+        assert r.status_code == 200
+        data = r.json()
+        assert data["items"] == []
+        assert data["total"] == 0
+        assert data["page"] == 1
+        assert data["size"] == 20
+        assert data["table_pending"] is True
+
     def test_invalid_dispatch_status_rejected(self, client):
         """非法 dispatch_status 應被拒絕（422）."""
         r = client.get("/api/v1/ai/governance/queue?dispatch_status=unknown")
@@ -579,6 +598,23 @@ class TestKmReviewDraftDedupe:
         )
         assert data["groups"][0]["archive_history"][0]["archived_count"] == 2
 
+    def test_endpoint_readback_exception_returns_empty_plan(self, client):
+        """KM dedupe 背景讀取失敗時應 fail-soft，不讓 Work Items 收到 500."""
+        with patch(
+            "src.api.v1.ai_governance.query_km_review_draft_dedupe",
+            new=AsyncMock(side_effect=RuntimeError("temporary dedupe read failure")),
+        ):
+            r = client.get("/api/v1/ai/governance/km-review-drafts/dedupe?limit=100")
+
+        assert r.status_code == 200
+        data = r.json()
+        assert data["schema_version"] == "km_review_draft_dedupe_v1"
+        assert data["total_review_drafts"] == 0
+        assert data["event_group_total"] == 0
+        assert data["duplicate_draft_total"] == 0
+        assert data["groups"] == []
+        assert data["generated_at"]
+
     def test_governance_event_tag_extraction(self):
         assert _extract_governance_event_id_from_tags([
             "agent:Hermes",