perf: dedup holdout four-way eval (baseline derive, best_hard memo)

tests/unit/test_runner_diag_tree_inject.py

@@ -212,6 +212,63 @@ async def test_diagnosis_reads_traces_from_steps_json(
     assert traces[0]["tool_name"] == "search_tree"
 
 
+def _fake_inference_result(accuracy: float) -> object:
+    """构造 InferenceResult 供 holdout 去重测试（per_task_type 空、token 归零）。"""
+    from app.harness.inference import InferenceResult
+
+    return InferenceResult(
+        run_id="x",
+        accuracy=accuracy,
+        total=10,
+        correct=int(accuracy * 10),
+        per_task_type={},
+        steps_mean=1.0,
+        token_usage={"prompt_tokens": 0, "completion_tokens": 0},
+        stop_reason_counts={},
+    )
+
+
+@pytest.mark.asyncio
+async def test_holdout_dedup_skips_reevaluated_versions(
+    runner_with_real_store: Runner,
+) -> None:
+    """baseline 不跑推理（从基线预测推导）；best_hard==final 时不重复评估。"""
+    from unittest.mock import AsyncMock
+
+    runner = runner_with_real_store
+    eval_calls: list[str] = []
+
+    async def _fake_eval(sv, pv, questions, run_id, context):  # noqa: ANN001
+        eval_calls.append(run_id)
+        return _fake_inference_result(0.5)
+
+    runner._eval_version_on_pool = AsyncMock(side_effect=_fake_eval)
+    # best_mixed 赢家取 final 版本（必落在 memo，0 推理）
+    runner._pick_mixed_best = AsyncMock(return_value=("skills_final", "prompts_final"))
+    # baseline 推导：patch 为 0 推理的假结果（不经 _eval_version_on_pool）
+    runner._derive_baseline_test_result = MagicMock(return_value=_fake_inference_result(0.4))
+
+    state = MagicMock()
+    state.holdout_memo = {}
+    state.baseline_skills_version = "skills_base"
+    state.baseline_prompts_version = "prompts_base"
+    # best_hard 版本 == final 版本 → 去重
+    state.best_skills_version = "skills_final"
+    state.best_prompts_version = "prompts_final"
+
+    pools = MagicMock()
+    pools.baseline_run_id = "infer_adhoc"
+    pools.test = [_fake_question("q1", "vA")]
+
+    await runner._holdout_four_way(
+        1, pools, state, eval_skills_version="skills_final", eval_prompts_version="prompts_final"
+    )
+
+    # baseline=0（推导）、best_hard=1（真评并存 memo）、final/best_mixed 引用 memo（0）
+    assert len(eval_calls) == 1
+    runner._derive_baseline_test_result.assert_called_once()
+
+
 @pytest.mark.asyncio
 async def test_run_step_deletes_stale_rows_before_rerun(
     runner_with_real_store: Runner, monkeypatch: pytest.MonkeyPatch