refactor(intelligent-eval): unify watchdog failures behind fail_eval seam

架构审查候选③（状态机归一）：_TRANSITIONS 成为评估状态机的唯一真相。

三个 watchdog（planning 双闸 / executing 兜底 / 触发失败闸门）原先直接
row.status = FAILED 绕过转换表、手工重复写字段。收编到新的公开接缝
fail_eval(session, eval_id, reason, decision_type, context)：表校验 →
repo CAS 条件写（status/plan_feedback/updated_at/completed_at 一条 SQL）
→ append_decision_log 留痕。

CAS 冲突（如用户在扫描间隙抢先取消）跳过并留日志，不当故障。API 路径
本已在表内，不动。新增 4 个契约测试，870 tests passed，零行为变化。

backend/agenteval/intelligent_eval/lifecycle.py

@@ -10,6 +10,7 @@
 非法转换抛 IntelligentEvalTransitionError，路由层映射为 409。
 """
 
+import logging
 from datetime import timedelta
 from typing import Any, Optional
 
@@ -558,7 +559,7 @@ def enforce_planning_gates(session: Session) -> int:
     """
     from sqlmodel import select
 
-    from agenteval.intelligent_eval.decision_logs import append_decision_log, count_decisions
+    from agenteval.intelligent_eval.decision_logs import count_decisions
     from agenteval.storage.db import IntelligentEvalDB
 
     now = utc_now().replace(tzinfo=None)
@@ -577,22 +578,15 @@ def enforce_planning_gates(session: Session) -> int:
             reason = f"planning 超过 {PLANNING_TIMEOUT_MINUTES} 分钟未提交粗计划，按 ADR-0011 双闸判失败"
         else:
             continue
-        row.status = IntelligentEvalStatus.FAILED.value
+        if fail_eval(
-        row.plan_feedback = reason
-        row.updated_at = utc_now()
-        row.completed_at = utc_now()
-        failed += 1
-        append_decision_log(
-            row.id,
-            "planning_gate_failed",
-            f"平台兜底：{reason}",
-            "platform",
-            {"platform_supplemented": True, "attempts": attempts, "age_minutes": int(age_minutes)},
             session,
-        )
+            row.id,
+            reason,
+            "planning_gate_failed",
+            {"attempts": attempts, "age_minutes": int(age_minutes)},
+        ):
+            failed += 1
 
-    if failed:
-        session.commit()
     return failed
 
 
@@ -619,7 +613,6 @@ def enforce_executing_ceiling(session: Session) -> int:
     """
     from sqlmodel import select
 
-    from agenteval.intelligent_eval.decision_logs import append_decision_log
     from agenteval.storage.db import IntelligentEvalDB
 
     now = utc_now().replace(tzinfo=None)
@@ -640,22 +633,15 @@ def enforce_executing_ceiling(session: Session) -> int:
             f"executing 超过 {row.time_window_hours}h 时间窗 + {EXECUTING_OVERRUN_GRACE_HOURS}h 宽限"
             "仍未完成，按 ADR-0011 判失败"
         )
-        row.status = IntelligentEvalStatus.FAILED.value
+        if fail_eval(
-        row.plan_feedback = reason
-        row.updated_at = utc_now()
-        row.completed_at = utc_now()
-        failed += 1
-        append_decision_log(
-            row.id,
-            "executing_timeout",
-            f"平台兜底：{reason}",
-            "platform",
-            {"platform_supplemented": True, "time_window_hours": row.time_window_hours},
             session,
-        )
+            row.id,
+            reason,
+            "executing_timeout",
+            {"time_window_hours": row.time_window_hours},
+        ):
+            failed += 1
 
-    if failed:
-        session.commit()
     return failed
 
 
@@ -792,21 +778,50 @@ def record_trigger_failures(session: Session, *, channel: str, eval_ids: list[st
     return recorded
 
 
-def _fail_eval(session: Session, row, reason: str, decision_type: str, context: dict[str, Any]) -> None:
+def fail_eval(session: Session, eval_id: str, reason: str, decision_type: str, context: dict[str, Any]) -> bool:
+    """watchdog 判失败的统一接缝：表校验 → CAS 条件写 → 决策日志留痕。
+
+    所有平台侧"置 failed"必须穿过这里——``_TRANSITIONS`` 是唯一真相，
+    条件写挡住并发竞争（如用户在扫描间隙抢先取消）。
+
+    Returns:
+        True 判失败成功；False 表示跳过（评估不存在、非法转换或 CAS 冲突
+        ——状态已被他人收敛，属正常竞争结局，仅留日志不当故障）。
+    """
     from agenteval.intelligent_eval.decision_logs import append_decision_log
 
-    row.status = IntelligentEvalStatus.FAILED.value
+    logger = logging.getLogger("agenteval")
-    row.plan_feedback = reason
+    repo = IntelligentEvalRepository(session)
-    row.updated_at = utc_now()
+    ev = repo.get(eval_id)
-    row.completed_at = utc_now()
+    if ev is None:
+        logger.info("fail_eval 跳过：评估 %s 已不存在", eval_id)
+        return False
+    if IntelligentEvalStatus.FAILED not in _TRANSITIONS.get(ev.status, set()):
+        logger.warning("fail_eval 被状态表挡下：%s 当前 %s，不允许转 failed", eval_id, ev.status.value)
+        return False
+    now = utc_now()
+    result = repo._compare_and_set_fields(
+        eval_id,
+        expected_status=ev.status,
+        values={
+            "status": IntelligentEvalStatus.FAILED.value,
+            "plan_feedback": reason,
+            "updated_at": now,
+            "completed_at": now,
+        },
+    )
+    if result.status is not CompareAndSetStatus.APPLIED:
+        logger.info("fail_eval 跳过：评估 %s 状态已被并发收敛（%s）", eval_id, result.status)
+        return False
     append_decision_log(
-        row.id,
+        eval_id,
         decision_type,
         f"平台兜底：{reason}",
         "platform",
         {"platform_supplemented": True, **context},
         session,
     )
+    return True
 
 
 def enforce_trigger_failure_gates(session: Session) -> int:
@@ -852,7 +867,9 @@ def enforce_trigger_failure_gates(session: Session) -> int:
             if len(failures) < TRIGGER_FAILURE_MAX:
                 continue
             reason = f"planner 连续触发失败 {len(failures)} 次，按 ADR-0011 判失败"
-            _fail_eval(session, row, reason, "trigger_failure_gate", {"channel": "planner", "failures": len(failures)})
+            if fail_eval(
+                session, row.id, reason, "trigger_failure_gate", {"channel": "planner", "failures": len(failures)}
+            ):
                 failed += 1
         else:
             last_assigned = session.exec(
@@ -868,9 +885,9 @@ def enforce_trigger_failure_gates(session: Session) -> int:
             if len(failures) < TRIGGER_FAILURE_MAX:
                 continue
             reason = f"worker 连续触发失败 {len(failures)} 次且期间无任务被认领，按 ADR-0011 判失败"
-            _fail_eval(session, row, reason, "trigger_failure_gate", {"channel": "worker", "failures": len(failures)})
+            if fail_eval(
+                session, row.id, reason, "trigger_failure_gate", {"channel": "worker", "failures": len(failures)}
+            ):
                 failed += 1
 
-    if failed:
-        session.commit()
     return failed

tests/unit/test_intelligent_eval_watchdog_characterization.py

@@ -498,3 +498,73 @@ def test_task_pickup_breaks_consecutive_worker_failures(db_session: Session):
 
     db_session.refresh(ev)
     assert ev.status == IntelligentEvalStatus.EXECUTING.value
+
+
+# ---------------------------------------------------------------------------
+# fail_eval 统一接缝契约（状态机归一）：watchdog 判失败必须穿过表校验 + CAS
+# ---------------------------------------------------------------------------
+
+
+def test_fail_eval_writes_fields_and_log(db_session: Session):
+    """fail_eval：CAS 条件写 status/plan_feedback/completed_at + 决策日志留痕。"""
+    from agenteval.intelligent_eval.lifecycle import fail_eval
+
+    ev = _make_executing_eval(db_session)
+    assert fail_eval(db_session, ev.id, "测试判败", "executing_timeout", {"k": 1}) is True
+
+    db_session.refresh(ev)
+    assert ev.status == IntelligentEvalStatus.FAILED.value
+    assert ev.plan_feedback == "测试判败"
+    assert ev.completed_at is not None
+    logs = db_session.exec(
+        select(IntelligentEvalDecisionLogDB).where(IntelligentEvalDecisionLogDB.eval_id == ev.id)
+    ).all()
+    assert len(logs) == 1
+    assert logs[0].decision_type == "executing_timeout"
+    assert logs[0].cron_id == "platform"
+
+
+def test_fail_eval_blocked_by_transition_table(db_session: Session):
+    """终态评估不允许再判 failed——_TRANSITIONS 是唯一真相。"""
+    from agenteval.intelligent_eval.lifecycle import fail_eval
+
+    ev = _make_executing_eval(db_session)
+    ev.status = IntelligentEvalStatus.COMPLETED.value
+    db_session.add(ev)
+    db_session.commit()
+
+    assert fail_eval(db_session, ev.id, "不该生效", "executing_timeout", {}) is False
+    db_session.refresh(ev)
+    assert ev.status == IntelligentEvalStatus.COMPLETED.value
+    logs = db_session.exec(
+        select(IntelligentEvalDecisionLogDB).where(IntelligentEvalDecisionLogDB.eval_id == ev.id)
+    ).all()
+    assert logs == []
+
+
+def test_fail_eval_skips_on_cas_conflict(db_session: Session, monkeypatch):
+    """CAS 冲突（用户抢先取消等并发收敛）→ 跳过不当故障，不写日志。"""
+    from agenteval.intelligent_eval.lifecycle import fail_eval
+    from agenteval.intelligent_eval.repository import (
+        CompareAndSetResult,
+        CompareAndSetStatus,
+        IntelligentEvalRepository,
+    )
+
+    ev = _make_executing_eval(db_session)
+    monkeypatch.setattr(
+        IntelligentEvalRepository,
+        "_compare_and_set_fields",
+        lambda self, eval_id, *, expected_status, values: CompareAndSetResult(status=CompareAndSetStatus.CONFLICT),
+    )
+
+    assert fail_eval(db_session, ev.id, "竞争失败", "executing_timeout", {}) is False
+    db_session.refresh(ev)
+    assert ev.status == IntelligentEvalStatus.EXECUTING.value
+
+
+def test_fail_eval_skips_unknown_eval(db_session: Session):
+    """评估不存在 → 跳过（NOT_FOUND 语义）。"""
+    from agenteval.intelligent_eval.lifecycle import fail_eval
+
+    assert fail_eval(db_session, "no-such-eval", "r", "executing_timeout", {}) is False