diff --git a/app/harness/log.py b/app/harness/log.py
index 7231abe..4cab15f 100644
--- a/app/harness/log.py
+++ b/app/harness/log.py
@@ -52,6 +52,9 @@ class HarnessLog:
         run_id: 本次运行的唯一标识。
         git_sha: 代码版本，默认自动获取。
         config_snapshot: 本次运行的配置快照。
+        register_run: 是否注册运行（upsert _runs + 退出时同步 status）。默认 True；
+            只读查询已有 run（如基线预测回读）时传 False，避免把该 run 的
+            started_at/config/status 改写、把基线元数据污染成本次进程的运行状态。
     """
 
     def __init__(
@@ -60,27 +63,33 @@ class HarnessLog:
         run_id: str,
         git_sha: str | None = None,
         config_snapshot: dict[str, Any] | None = None,
+        *,
+        register_run: bool = True,
     ) -> None:
         self._run_id = run_id
+        self._register_run = register_run
         Path(db_path).parent.mkdir(parents=True, exist_ok=True)
         self._conn = sqlite3.connect(db_path, check_same_thread=False)
         self._lock = threading.Lock()
         self._conn.row_factory = sqlite3.Row
         self._conn.execute("PRAGMA journal_mode=WAL")
         self._init_fixed_tables()
-        resolved_sha = git_sha or _get_git_sha()
-        config_json = json.dumps(config_snapshot, ensure_ascii=False) if config_snapshot else None
-        self._conn.execute(
-            "INSERT INTO _runs"
-            " (run_id, git_sha, started_at, config, status)"
-            " VALUES (?, ?, ?, ?, ?)"
-            " ON CONFLICT(run_id) DO UPDATE SET"
-            " started_at=excluded.started_at,"
-            " config=excluded.config,"
-            " status=excluded.status",
-            (run_id, resolved_sha, _now_iso(), config_json, "running"),
-        )
-        self._conn.commit()
+        if register_run:
+            resolved_sha = git_sha or _get_git_sha()
+            config_json = (
+                json.dumps(config_snapshot, ensure_ascii=False) if config_snapshot else None
+            )
+            self._conn.execute(
+                "INSERT INTO _runs"
+                " (run_id, git_sha, started_at, config, status)"
+                " VALUES (?, ?, ?, ?, ?)"
+                " ON CONFLICT(run_id) DO UPDATE SET"
+                " started_at=excluded.started_at,"
+                " config=excluded.config,"
+                " status=excluded.status",
+                (run_id, resolved_sha, _now_iso(), config_json, "running"),
+            )
+            self._conn.commit()
 
     def _init_fixed_tables(self) -> None:
         """创建 _runs 和 _events 固定表。"""
@@ -217,13 +226,18 @@ class HarnessLog:
 
         参数:
             status: 最终状态，"completed" 或 "failed"。
+
+        关键实现:
+            register_run=False（只读打开）时跳过 status 更新，仅关闭连接，
+            避免只读回读把已有 run 的 finished_at/status 改写。
         """
         with self._lock:
-            self._conn.execute(
-                "UPDATE _runs SET finished_at = ?, status = ? WHERE run_id = ?",
-                (_now_iso(), status, self._run_id),
-            )
-            self._conn.commit()
+            if self._register_run:
+                self._conn.execute(
+                    "UPDATE _runs SET finished_at = ?, status = ? WHERE run_id = ?",
+                    (_now_iso(), status, self._run_id),
+                )
+                self._conn.commit()
             self._conn.close()
 
     def __enter__(self) -> HarnessLog:
diff --git a/app/harness/pools.py b/app/harness/pools.py
index 89763de..1606c28 100644
--- a/app/harness/pools.py
+++ b/app/harness/pools.py
@@ -797,7 +797,9 @@ def build_or_load_pools(
                     # 增量构建新类别
                     paths = resolve_paths(config.workspace_dir)
                     questions = load_benchmark(paths.questions_dir)
-                    with HarnessLog(str(db_path), baseline_run_id) as hlog:
+                    with HarnessLog(
+                        str(db_path), baseline_run_id, register_run=False
+                    ) as hlog:
                         rows = hlog.query(
                             "SELECT question_id, prediction, answer "
                             "FROM predictions WHERE run_id=?",
@@ -872,7 +874,7 @@ def build_or_load_pools(
     # ── 全新构建 ──
     paths = resolve_paths(config.workspace_dir)
     questions = load_benchmark(paths.questions_dir)
-    with HarnessLog(str(db_path), baseline_run_id) as hlog:
+    with HarnessLog(str(db_path), baseline_run_id, register_run=False) as hlog:
         rows = hlog.query(
             "SELECT question_id, prediction, answer FROM predictions WHERE run_id=?",
             (baseline_run_id,),
diff --git a/app/harness/runner.py b/app/harness/runner.py
index 463f52e..f468e12 100644
--- a/app/harness/runner.py
+++ b/app/harness/runner.py
@@ -920,7 +920,9 @@ class Runner:
         self._gate_units_by_id: dict[str, QuestionUnit] = {
             u.unit_id: u for u in build_units(questions)
         }
-        with HarnessLog(str(self._paths.db_path), pools.baseline_run_id) as log:
+        with HarnessLog(
+            str(self._paths.db_path), pools.baseline_run_id, register_run=False
+        ) as log:
             rows = log.query(
                 "SELECT question_id, prediction, answer FROM predictions WHERE run_id=?",
                 (pools.baseline_run_id,),
diff --git a/tests/unit/test_harness_log.py b/tests/unit/test_harness_log.py
index 5e90855..35a0e84 100644
--- a/tests/unit/test_harness_log.py
+++ b/tests/unit/test_harness_log.py
@@ -215,6 +215,30 @@ class TestHarnessLogUpsert:
             rows = log3.query("SELECT COUNT(*) as cnt FROM _runs WHERE run_id='run_1'")
             assert rows[0]["cnt"] == 1
 
+    def test_register_run_false_skips_upsert(self, tmp_path: Path) -> None:
+        """register_run=False 时只读打开不改写已有 _runs 行（started_at/status 不变）。"""
+        db = str(tmp_path / "h.db")
+
+        def _read_run_row(run_id: str) -> dict:
+            # 用 register_run=False 只读，避免读取本身污染 _runs
+            with HarnessLog(db, run_id, register_run=False) as log:
+                rows = log.query(
+                    "SELECT started_at, status FROM _runs WHERE run_id=?", (run_id,)
+                )
+            return rows[0]
+
+        with HarnessLog(db, "r1"):
+            pass  # 初次注册 + 正常退出置 completed
+        row0 = _read_run_row("r1")
+
+        time.sleep(0.02)
+        with HarnessLog(db, "r1", register_run=False) as log:
+            log.query("SELECT 1")  # 只读
+        row1 = _read_run_row("r1")
+
+        assert row1["started_at"] == row0["started_at"]
+        assert row1["status"] == row0["status"]
+
 
 # ===========================================================================
 # RunLogImpl 测试