fix(governance): normalize knowledge degradation payloads

apps/api/tests/test_failover_alerter.py

@@ -294,6 +294,38 @@ def test_governance_alert_card_formats_knowledge_degradation() -> None:
     assert "欄位快覽" not in card
 
 
+def test_governance_alert_card_accepts_legacy_knowledge_degradation_payload() -> None:
+    card = format_governance_alert_card(
+        "knowledge_degradation",
+        {
+            "status": "warning",
+            "stale_count": 1425,
+            "total": 1856,
+            "stale_ratio": 0.768,
+            "threshold": 0.2,
+            "stale_days": 7,
+            "remediation": [
+                "啟動 KM 反查與自動補齊流程",
+                "關鍵服務告警自動同步到 KM 任務",
+            ],
+            "next_step": "run_kb_growth_healthcheck",
+            "automatable_work": [
+                "每日檢查 ANTI_PATTERN 更新結果",
+                "安排至少 2 位 owner 對 stale 條目做快速人工審核",
+            ],
+        },
+    )
+
+    assert "1425 / 1856 筆 KM" in card
+    assert "陳舊 KM：1425" in card
+    assert "總 KM：1856" in card
+    assert "陳舊比例：76\\.8%" in card
+    assert "▶️ 下一步：run\\_kb\\_growth\\_healthcheck" in card
+    assert "每日檢查 ANTI\\_PATTERN 更新結果" in card
+    assert "📎 *補充欄位*" not in card
+    assert "? / ?" not in card
+
+
 def test_governance_alert_card_limits_fallback_fields() -> None:
     card = format_governance_alert_card(
         "custom_signal",