feat(wave2+km): LLM 動態按鈕啟用 + KM 自動寫入 + AI Router dead code 標記

- ConfigMap: USE_LLM_DYNAMIC_BUTTONS=true（B2/B3/B4 handler 全就緒）
- decision_manager: auto_execute 失敗路徑補 KM fire-and-forget 寫入
- ai_router: _build_fallback_chain 標記 DEPRECATED 2026-04-28
- tests: test_golden_regression.py 新增 172 行 golden 回歸測試

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/api/src/services/ai_router.py

@@ -599,6 +599,7 @@ class AIRouter:
         self, selected_provider: AIProviderEnum
     ) -> list[tuple[AIProviderEnum, str]]:
         """
+        # DEPRECATED 2026-04-28 — 已由 _build_fallback_chain_for_intent 取代，無呼叫方
         建立 Fallback 鏈 (排除已選 Provider)
 
         Fallback 順序: Ollama → Gemini → Claude

apps/api/src/services/decision_manager.py

@@ -2098,6 +2098,11 @@ class DecisionManager:
         except Exception as _cd_err:
             logger.debug("auto_execute_cooldown_check_error", error=str(_cd_err))
 
+        # P1.1 fix 2026-04-27 ogt + Claude Sonnet 4.6: 失敗路徑 KM 寫入哨兵
+        # 在 try 外宣告，確保 except 區塊能存取（即使建構失敗）
+        _km_executor = None
+        _km_approval = None
+
         try:
             # 延遲導入避免循環依賴
             from src.models.approval import ApprovalRequest, ApprovalStatus
@@ -2119,6 +2124,7 @@ class DecisionManager:
                 risk_level=_risk,
                 matched_playbook_id=_matched_playbook_id,
             )
+            _km_approval = approval  # P1.1: 供 except 失敗路徑使用
 
             # ADR-071-I: 執行前抓 metrics_before 快照 (2026-04-11 Claude Sonnet 4.6)
             _metrics_before = await _fetch_metrics_snapshot(incident)
@@ -2144,6 +2150,7 @@ class DecisionManager:
             #        _push_auto_repair_result → Telegram 顯示 ✅ 自動修復完成，即使 K8s 拒絕了指令
             # 修復: execute_approved_action 現在返回 bool，正確透傳給通知函數
             executor = ApprovalExecutionService()
+            _km_executor = executor  # P1.1: 供 except 失敗路徑使用
             _exec_success = await executor.execute_approved_action(approval)
 
             # 更新狀態
@@ -2190,6 +2197,16 @@ class DecisionManager:
                 _push_decision_to_telegram(incident, token.proposal_data)
             )
 
+            # P1.1 fix 2026-04-27 ogt + Claude Sonnet 4.6: 失敗路徑補 KM 寫入
+            # 根因：auto_execute 拋出例外時，學習飛輪完全拿不到失敗記錄
+            # 修法：若 executor/approval 已建立，fire-and-forget 寫入失敗 KM；未建立則跳過
+            if _km_executor is not None and _km_approval is not None:
+                _fire_and_forget(
+                    _km_executor._write_execution_result_to_km(
+                        _km_approval, False, str(e)
+                    )
+                )
+
     async def _query_kb_context_inner(self, incident: Incident) -> str:
         """KB RAG 實際查詢邏輯，由 _query_kb_context 包裝 timeout 後呼叫"""
         query_parts = list(incident.affected_services)