feat(wave6-8): P2.1 fusion + P2.2 governance + P2.4 consensus + Wave 7/8 BLOCKER 修復

承接 Wave 6/7/8 多 engineer 在 agent 限額前完成的代碼，補 commit 解 production
HEAD 隱性 import error（decision_fusion 已被 decision_manager 引用但檔案 untracked）。

新增（後端核心）:
- decision_fusion.py (562 行) — P2.1 方法 III（OpenClaw + Hermes + Elephant 三 LLM 融合）
- aiops_timeline.py + aiops_timeline_service.py — critic B4 修復
  /api/v1/aiops/timeline endpoint，DB 存取抽到 service 層遵守 leWOOOgo 積木化
- migrations/p2_decision_fusion_columns.sql + rollback — approval_records fusion 欄位

修改（後端整合）:
- decision_manager.py — fusion 三斷鏈修補（critic B1+B2+B3）：
  · B1: 寫 _evidence_snapshot_ref 到 token.proposal_data
  · B2: fusion 前計算 complexity_score 並寫 token
  · B3: fusion composite 寫 token.proposal_data["decision_fusion"]
- auto_approve.py — fusion + consensus 認識（critic B3+B5）：
  · composite > 0.7 → auto_execute_eligible bypass min_confidence
  · source=consensus_engine + score>=0.6 → 規則可信路徑
- consensus_engine.py — db-fix _save_consensus 重用 agent_sessions
- governance_agent.py — db-fix _alert PG 寫入 ai_governance_events
- approval_db.py — fusion 3 欄位 + 2 partial index + CheckConstraint
- db/models.py — schema 對齊 migration
- core/config.py — vuln #1 修復：OLLAMA_URL/_FALLBACK_URL field_validator
  拒絕公網 IP + 外部域名，僅允許私網/loopback/K8s SVC 白名單
- core/feature_flags.py — P2 fusion + consensus flags
- main.py — governance_agent lifespan 啟動
- failover_alerter.py — Wave8-X2: in-memory dedup fallback（Redis 拒絕後不 fail-open）
- ollama_*.py — metrics 整合 + recovery 改善
- auto_repair_service.py — verifier 接線

新增（測試 2438 行）:
- test_decision_fusion.py / test_governance_agent.py / test_consensus_integration.py
- test_p2_db_fixes.py / test_wave8_fusion_fixes.py
- test_config_url_validation.py（vuln #1 12 tests）
- test_failover_alerter.py +Wave8-X2 in-memory dedup 補測

驗收: 116 tests pass (decision_fusion + wave8_fusion + config_url + consensus +
                      governance + p2_db_fixes + failover_alerter)

Conflict resolution:
- 3 檔（config.py + auto_approve.py + decision_manager.py）git stash pop 衝突
  保留 stashed (engineer 最終版)，補回 ValueError 「公網 IP」字樣對齊 test

Note: 此 commit 解 production HEAD 隱性 import error
仍未修: vuln #4 prompt injection / debugger B14 quota fail-closed
       / B25-B26 drain_pending_tasks / B8 governance fail alert

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Co-Authored-By: Multiple Engineers (Wave 6/7/8) <noreply@anthropic.com>

apps/api/src/services/governance_agent.py

@@ -22,6 +22,7 @@ from sqlalchemy import func, select
 
 from src.db.base import get_db_context
 from src.db.models import (
+    AiGovernanceEvent,
     AutoRepairExecution,
     IncidentEvidence,
     KnowledgeEntryRecord,
@@ -261,13 +262,29 @@ class GovernanceAgent:
             try:
                 results[check_name] = await check_func()
             except Exception as e:
-                logger.warning(
+                logger.exception(
                     "governance_check_failed",
                     check=check_name,
                     error=str(e),
                 )
                 results[check_name] = {"error": str(e)}
 
+        # 2026-04-27 Wave8-X3 by Claude — B8 全失敗聚合告警
+        # ≥3 項失敗代表治理機制本身故障，必須送出緊急告警
+        failed_checks = [k for k, v in results.items() if isinstance(v, dict) and "error" in v]
+        if len(failed_checks) >= 3:
+            try:
+                await self._alert(
+                    "governance_self_failure",
+                    {
+                        "failed_checks": failed_checks,
+                        "total_checks": 4,
+                        "errors": {k: results[k].get("error") for k in failed_checks},
+                    },
+                )
+            except Exception:
+                logger.exception("governance_self_failure_alert_failed")
+
         logger.info("governance_self_check_complete", results=results)
         return results
 
@@ -276,10 +293,27 @@ class GovernanceAgent:
     # =========================================================================
 
     async def _alert(self, event_type: str, payload: dict[str, Any]) -> None:
-        """structlog 告警 + Telegram 推送（via FailoverAlerter）
+        """structlog 告警 + PG 持久化 + Telegram 推送（via FailoverAlerter）
 
         2026-04-26 P2.2 by Claude
+        2026-04-26 P2-DB-Fix by Claude — db-expert P0 三修（P0.1）: 補 PG 寫入 ai_governance_events
+        ADR-085 鐵律：AI 學習成果不可存 Cache，必須落地 PG
         """
+        # 1. 寫 PG（ADR-085 鐵律 — 失敗不阻斷主流程）
+        try:
+            from sqlalchemy import insert as _sa_insert
+            async with get_db_context() as db:
+                await db.execute(
+                    _sa_insert(AiGovernanceEvent).values(
+                        event_type=event_type,
+                        details=payload,
+                    )
+                )
+                await db.commit()
+        except Exception as _pg_err:
+            logger.warning("governance_pg_write_failed", error=str(_pg_err))
+
+        # 2. structlog（保留既有行為）
         logger.warning("governance_alert", event_type=event_type, **payload)
 
         # Lazy import：延遲到實際呼叫時才取 alerter，避免啟動時循環依賴