feat(auto-rate): rule_engine 路徑開啟自動執行，預計 42% → 70%+

修法 3（debugger 建議）：CS2 is_rule_based=True + kubectl 有值 + 非 CRITICAL/DESTRUCTIVE → 直接 auto-execute，不建 PENDING record

安全防線（5 層）：
- CRITICAL risk → 絕對不自動執行
- _DESTRUCTIVE_PATTERNS 命中 → 絕對不自動執行
- NO_ACTION → 不執行
- kubectl 空字串 → 不執行
- 任何例外 → catch + 降級到 PENDING，不 crash

15 tests 驗收（1487 passed）

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

apps/api/src/api/v1/webhooks.py

@@ -1334,6 +1334,62 @@ async def _process_new_alert_background(
             except Exception as _shadow_err_cs2:
                 logger.warning("shadow_auto_approve_failed", error=str(_shadow_err_cs2))
 
+            # 2026-04-27 ogt + Claude Sonnet 4.6: CS2 規則引擎自動執行
+            # 設計：is_rule_based=True 確定性高，滿足條件直接執行，不等人工審核
+            # 安全防線：CRITICAL / destructive patterns / NO_ACTION / 空 kubectl → 全部降級 PENDING
+            try:
+                from src.services.auto_approve import _DESTRUCTIVE_PATTERNS
+                from src.models.approval import ApprovalRequest, ApprovalStatus
+                from src.services.approval_execution import ApprovalExecutionService
+
+                _destructive_set = set(p.lower() for p in _DESTRUCTIVE_PATTERNS)
+                _can_auto = (
+                    bool(rule_kubectl)
+                    and rule_risk != RiskLevel.CRITICAL
+                    and not any(p in rule_kubectl.lower() for p in _destructive_set)
+                    and "NO_ACTION" not in rule_action
+                )
+                if _can_auto:
+                    _auto_approval = ApprovalRequest(
+                        incident_id=None,  # 尚未建立，稍後 update_incident_id 補上
+                        action=rule_action,
+                        description=approval_create.description,
+                        requested_by="auto_approve_rule_engine",
+                        required_signatures=0,
+                        status=ApprovalStatus.APPROVED,
+                        risk_level=rule_risk.value,
+                        matched_playbook_id=_approval_metadata_cs2.get("playbook_id"),
+                    )
+                    # 使用 DB 中剛建立的 approval.id 讓 executor 可回寫
+                    _auto_approval.id = approval.id
+
+                    _cs2_executor = ApprovalExecutionService()
+                    _cs2_exec_success = await _cs2_executor.execute_approved_action(_auto_approval)
+
+                    # 更新 DB approval 執行狀態
+                    try:
+                        await service.update_execution_status(approval.id, _cs2_exec_success)
+                    except Exception as _upd_err:
+                        logger.warning(
+                            "cs2_auto_execute_status_update_failed",
+                            approval_id=str(approval.id),
+                            error=str(_upd_err),
+                        )
+
+                    logger.info(
+                        "rule_engine_auto_executed",
+                        approval_id=str(approval.id),
+                        rule_id=rule_response.get("rule_id", "unknown"),
+                        kubectl=rule_kubectl,
+                        exec_success=_cs2_exec_success,
+                    )
+            except Exception as _auto_err:
+                logger.warning(
+                    "cs2_auto_execute_failed_degraded_to_pending",
+                    approval_id=str(approval.id),
+                    error=str(_auto_err),
+                )
+
             incident_id = await create_incident_for_approval(
                 approval_id=str(approval.id),
                 risk_level=rule_risk.value,