diff --git a/app/api/search.py b/app/api/search.py
index 2b888ba..431f0c3 100644
--- a/app/api/search.py
+++ b/app/api/search.py
@@ -582,6 +582,22 @@ async def ask(
             ),
         ),
     ] = None,
+    corpus_variant: str | None = Query(
+        None,
+        pattern=r"^(prehier|hier_sim_raw|hier_sim_clean)$",
+        description=(
+            "⚠️ EVAL-ONLY (Hier-PassageRAG-Diagnose-1). evidence retrieval 의 chunk leg 를 측정 뷰로 "
+            "교체 — prehier(legacy) | hier_sim_raw | hier_sim_clean. 운영 UI 미사용. "
+            "미지정 = production corpus_chunks (기존 /ask 동작 동일)."
+        ),
+    ),
+    exact_knn: bool = Query(
+        False,
+        description=(
+            "⚠️ EVAL-ONLY (Hier-PassageRAG-Diagnose-1). vector leg exact KNN (ivfflat 근사 제거). "
+            "passage 변종 공정 비교용. 운영 미사용. 미지정(false) = 기존 /ask 동작 동일."
+        ),
+    ),
     x_source: Annotated[str | None, Header(alias="X-Source")] = None,
     x_eval_case_id: Annotated[str | None, Header(alias="X-Eval-Case-Id")] = None,
     x_eval_token: Annotated[str | None, Header(alias="X-Eval-Token")] = None,
@@ -601,10 +617,11 @@ async def ask(
     defense_log: dict = {}  # per-layer flag snapshot
     source, eval_case_id = _resolve_eval_identity(x_source, x_eval_case_id, x_eval_token)
 
-    # 1. 검색 파이프라인
+    # 1. 검색 파이프라인 (corpus_variant/exact_knn = EVAL-ONLY, 미지정 시 기존 동작 동일)
     pr = await run_search(
         session, q, mode="hybrid", limit=limit,
         fusion=DEFAULT_FUSION, rerank=True, analyze=True,
+        corpus_variant=corpus_variant, exact_knn=exact_knn,
     )
 
     # 1.5. ask_includable=false 문서를 evidence 입력에서 제외