diff --git a/services/analysis-engine/tests/test_separation.py b/services/analysis-engine/tests/test_separation.py
index 33dceff6..81e27cc1 100644
--- a/services/analysis-engine/tests/test_separation.py
+++ b/services/analysis-engine/tests/test_separation.py
@@ -97,7 +97,7 @@ def test_stem_separator_deduplicates() -> None:
 def test_stem_separator_invalid_role() -> None:
     """Test separator handles non-dict roles gracefully."""
     separator = StemSeparator()
-    result = separator.separate(
+    result = separator.separate(  # type: ignore[arg-type]
         [{"id": "bass", "name": "Bass", "roleType": "instrument"}, "invalid"]
     )
     assert len(result["stems"]) == 1
@@ -135,6 +135,16 @@ def test_stem_separator_keyboard_name_match() -> None:
     assert result["stems"][0]["category"] == "keys"
 
 
+def test_stem_separator_missing_id() -> None:
+    """Test separator handles roles with missing id by generating a fallback id."""
+    separator = StemSeparator()
+    roles = [{"name": "Lead Vocal", "roleType": "vocal"}]
+    result = separator.separate(roles)
+    assert len(result["stems"]) == 1
+    assert result["stems"][0]["stem_id"] == "stem-role-0"
+    assert result["stems"][0]["label"] == "Lead Vocal"
+
+
 def test_audio_stem_separator_splits_local_audio_into_chunked_stems(tmp_path) -> None:
     """Ensure local audio is separated into downstream-consumable canonical stems."""
     sample_rate = 8_000