diff --git a/app/services/search/search_pipeline.py b/app/services/search/search_pipeline.py
index 996737f..b9273b2 100644
--- a/app/services/search/search_pipeline.py
+++ b/app/services/search/search_pipeline.py
@@ -32,6 +32,8 @@ from typing import TYPE_CHECKING, Literal
 
 from sqlalchemy.ext.asyncio import AsyncSession
 
+from core.database import async_session
+
 from . import query_analyzer, query_rewriter
 from .fusion_service import (
     DEFAULT_FUSION,
@@ -188,6 +190,7 @@ async def run_search(
             snapshot_chunk_id_max=snapshot_chunk_id_max,
             reranker_backend=reranker_backend,
             rewrite_backend=rewrite_backend,
+            axis=axis,
         )
 
     timing: dict[str, float] = {}
@@ -536,6 +539,7 @@ async def search_with_rewrite(
     snapshot_chunk_id_max: int | None,
     reranker_backend: str | None,
     rewrite_backend: str,
+    axis: "AxisFilter | None" = None,
 ) -> PipelineResult:
     """Phase 2Q multi-query retrieval 합성 path (plan v6 §5.5).
 
@@ -579,13 +583,20 @@ async def search_with_rewrite(
     async def _variant_retrieve(
         v: str,
     ) -> "tuple[list[SearchResult], list[SearchResult], dict[int, list[SearchResult]]]":
-        text = await search_text(session, v, per_variant_k)
-        raw_chunks = await search_vector(
-            session, v, per_variant_k,
-            embedding_backend=embedding_backend,
-            snapshot_doc_id_max=snapshot_doc_id_max,
-            snapshot_chunk_id_max=snapshot_chunk_id_max,
-        )
+        # 변형별 독립 AsyncSession (fan-out). 공유 session 을 asyncio.gather 로 동시
+        # execute 에 넘기면 SQLAlchemy async 가 'another operation in progress' 로
+        # 부하 의존적 비결정 크래시 — variant 마다 독립 연결로 분리한다.
+        # axis(material_type/jurisdiction/year) 도 single-query path 와 동일하게 전달
+        # (rewrite 경로가 axis 필터를 조용히 누락하던 결함 수정).
+        async with async_session() as vsession:
+            text = await search_text(vsession, v, per_variant_k, axis=axis)
+            raw_chunks = await search_vector(
+                vsession, v, per_variant_k,
+                embedding_backend=embedding_backend,
+                snapshot_doc_id_max=snapshot_doc_id_max,
+                snapshot_chunk_id_max=snapshot_chunk_id_max,
+                axis=axis,
+            )
         vector, chunks_by_doc = compress_chunks_to_docs(raw_chunks, per_variant_k)
         return text, vector, chunks_by_doc
 
diff --git a/app/services/study/explanation_rag.py b/app/services/study/explanation_rag.py
index dc088b1..4e3616d 100644
--- a/app/services/study/explanation_rag.py
+++ b/app/services/study/explanation_rag.py
@@ -252,12 +252,15 @@ async def gather_explanation_context(
     client = AIClient()
     query = _build_query(question)
     try:
-        # 두 조회 병렬화 (rerank 호출이 별개라 lock 충돌 없음)
-        docs, questions = await asyncio.gather(
-            _gather_document_evidence(session, user_id, question.study_topic_id, query, client),
-            _gather_question_evidence(
-                session, user_id, question.study_topic_id, question.id, query, client
-            ),
+        # 같은 AsyncSession 을 asyncio.gather 로 동시 execute 에 넘기면 SQLAlchemy async 가
+        # 'another operation in progress' 로 부하 의존적 비결정 크래시(이전 주석 'lock 충돌
+        # 없음' 은 rerank HTTP 만 보고 DB execute 동시성을 간과한 오인). 백그라운드 prefetch
+        # 라 순차 직렬화 — 사용자 대면 rewrite 경로(독립 세션 fan-out)와는 다른 처방.
+        docs = await _gather_document_evidence(
+            session, user_id, question.study_topic_id, query, client
+        )
+        questions = await _gather_question_evidence(
+            session, user_id, question.study_topic_id, question.id, query, client
         )
         return ExplanationContext(documents=docs, questions=questions)
     finally:
diff --git a/app/services/study/subject_note_rag.py b/app/services/study/subject_note_rag.py
index 17bcfeb..0f398bb 100644
--- a/app/services/study/subject_note_rag.py
+++ b/app/services/study/subject_note_rag.py
@@ -238,9 +238,13 @@ async def gather_subject_note_context(
     client = AIClient()
     query = _build_query(subject, scope)
     try:
-        docs, questions = await asyncio.gather(
-            _gather_document_evidence(session, user_id, study_topic_id, query, client),
-            _gather_question_evidence(session, user_id, study_topic_id, subject, scope, query, client),
+        # 같은 AsyncSession 동시 execute 회피 — 순차 직렬화(백그라운드 prefetch).
+        # explanation_rag.gather_explanation_context 와 동형(R2 공유세션 동시성 수정).
+        docs = await _gather_document_evidence(
+            session, user_id, study_topic_id, query, client
+        )
+        questions = await _gather_question_evidence(
+            session, user_id, study_topic_id, subject, scope, query, client
         )
         return SubjectNoteContext(documents=docs, questions=questions)
     finally: