test(normalizer): cover AliasIndex unambiguous first-name resolution

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tools/import-normalizer/tests/test_persons.py

@@ -71,3 +71,14 @@ def test_alias_index_suggestion():
     idx = persons.AliasIndex(people)
     sid, score = idx.suggest("Hans Wittkop")  # typo
     assert sid == people[0].person_id and score >= config.FUZZY_SUGGEST_THRESHOLD
+
+def test_alias_index_first_name_only_when_unambiguous():
+    people = persons.parse_register([
+        {"last_name": "Cram", "first_name": "Clara"},
+        {"last_name": "de Gruyter", "first_name": "Walter"},
+        {"last_name": "Cram", "first_name": "Walter"},  # 2nd "Walter" -> first name ambiguous
+    ])
+    idx = persons.AliasIndex(people)
+    assert idx.resolve("Clara") == people[0].person_id   # unique first name resolves
+    assert idx.resolve("Walter") is None                 # ambiguous first name does NOT resolve
+    assert idx.display(people[0].person_id) == "Clara Cram"