Preserve valid flags when merging datasets

Without this, merging validated datasets dropped the per-episode valid
flag, so a later convert --valid-only would include episodes already
known to be invalid.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LYnRMrL29hDAgjePm2DgZJ

Author: k1000dai

src/openarm_dataset/merge.py

@@ -131,13 +131,14 @@ def _build_merged_episodes(
 
     for ds_idx, ds in enumerate(datasets):
         for ep in ds.meta.episodes:
-            merged_episodes.append(
-                {
-                    "id": str(len(merged_episodes)),
-                    "success": ep["success"],
-                    "task_index": task_index_maps[ds_idx][ep["task_index"]],
-                }
-            )
+            merged_episode = {
+                "id": str(len(merged_episodes)),
+                "success": ep["success"],
+                "task_index": task_index_maps[ds_idx][ep["task_index"]],
+            }
+            if "valid" in ep:
+                merged_episode["valid"] = ep["valid"]
+            merged_episodes.append(merged_episode)
 
     return merged_episodes
 

tests/test_merge.py

@@ -56,6 +56,20 @@ def test_merge_two_datasets(dataset_a, dataset_b, tmp_path):
         assert (output / "episodes" / str(i)).is_dir()
 
 
+def test_merge_preserves_valid_flags(dataset_a, dataset_b, tmp_path):
+    meta_a = _load_meta(dataset_a)
+    for episode, valid in zip(meta_a["episodes"], (False, True)):
+        episode["valid"] = valid
+    with open(dataset_a / "metadata.yaml", "w") as f:
+        yaml.safe_dump(meta_a, f)
+
+    output = tmp_path / "merged"
+    merge_datasets([dataset_a, dataset_b], output)
+
+    meta = _load_meta(output)
+    assert [ep.get("valid") for ep in meta["episodes"]] == [False, True, None, None]
+
+
 def test_merge_preserves_metadata_from_first_dataset(dataset_a, dataset_b, tmp_path):
     meta_a = _load_meta(dataset_a)
     output = tmp_path / "merged"