fix: slow-update R2 dual_metric uses slow_candidate kind (not final)

tests/unit/test_harness_observation.py

@@ -71,6 +71,37 @@ def test_write_read_dual_metric(db_path: str, run_id: str) -> None:
     assert row["run_id"] == run_id
 
 
+def test_dual_metric_kinds_distinguishable(db_path: str, run_id: str) -> None:
+    """observation 层接受任意 version_kind：final 与 slow_candidate 可区分共存。"""
+    write_dual_metric(
+        db_path,
+        run_id=run_id,
+        epoch=1,
+        version_kind="final",
+        skills_version="v1",
+        prompts_version="v1",
+        pool="val",
+        hard_acc=0.7,
+        soft_score=None,
+        mixed_score=None,
+    )
+    write_dual_metric(
+        db_path,
+        run_id=run_id,
+        epoch=1,
+        version_kind="slow_candidate",
+        skills_version="v2",
+        prompts_version="v2",
+        pool="val",
+        hard_acc=0.6,
+        soft_score=None,
+        mixed_score=None,
+    )
+    rows = read_dual_metric(db_path, run_id=run_id)
+    kinds = {row["version_kind"] for row in rows if row["epoch"] == 1}
+    assert kinds == {"final", "slow_candidate"}
+
+
 # ---------------------------------------------------------------------------
 # shadow_gate
 # ---------------------------------------------------------------------------