Reject overlapping SearchQA manifest ids

Runnable SearchQA splits should remain disjoint. A duplicate manifest id across train, val, or test previously collapsed into the wanted-id set and reused the same row in multiple output splits without warning.

Constraint: Preserve manifest order and output schema for valid manifests.

Rejected: Deduplicate automatically | hiding split overlap would make evaluation contamination harder to notice.

Confidence: high

Scope-risk: narrow

Reversibility: clean

Directive: Fail fast on split-manifest integrity problems instead of repairing them silently.

Tested: uv run --with pytest pytest tests/test_materialize_searchqa.py -q

Tested: uv run --with ruff ruff check scripts/materialize_searchqa.py tests/test_materialize_searchqa.py

Not-tested: Loading the live Hugging Face dataset.

tests/test_materialize_searchqa.py

@@ -64,3 +64,16 @@ def test_materialize_searchqa_splits_fails_on_missing_manifest_id(tmp_path):
             {"train": [_row("a")]},
             dataset_name="example/searchqa",
         )
+
+
+def test_materialize_searchqa_splits_rejects_duplicate_manifest_ids(tmp_path):
+    manifest_dir = tmp_path / "manifest"
+    _write_manifest(manifest_dir, {"train": ["a"], "val": ["a"], "test": []})
+
+    with pytest.raises(ValueError, match="duplicate IDs"):
+        materialize_searchqa_splits(
+            manifest_dir,
+            tmp_path / "out",
+            {"train": [_row("a")]},
+            dataset_name="example/searchqa",
+        )