diff --git a/app/services/hier_decomp/persist.py b/app/services/hier_decomp/persist.py
new file mode 100644
index 0000000..ec32bf7
--- /dev/null
+++ b/app/services/hier_decomp/persist.py
@@ -0,0 +1,79 @@
+"""Hier tree → document_chunks 영속화 (PR-DocSrv-Hierarchical-Decomposition-1 c4).
+
+build_hier_tree 결과를 document_chunks 에 insert. source_type='hier_section',
+in_corpus=false(검색 비활성), is_leaf 노드만 embedding. 재실행 idempotent(기존 hier 행 삭제 후 재삽입).
+chunk_index = doc 별 (max+1) offset → 기존 legacy 와 (doc_id,chunk_index) unique 충돌 회피.
+c4(pilot)/c6(replace)/향후 backfill 공용.
+"""
+from __future__ import annotations
+from typing import Awaitable, Callable
+from sqlalchemy import text
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from services.hier_decomp.builder import build_hier_tree, coverage_stats
+
+CHUNKER_VERSION = "hier-rule-v1"
+SOURCE_TYPE = "hier_section"
+
+
+async def persist_hier_tree(
+    session: AsyncSession,
+    doc_id: int,
+    source_text: str,
+    embed_leaf: Callable[[str], Awaitable[list[float] | None]],
+    *,
+    domain_category: str | None = None,
+) -> dict:
+    """doc 의 hier_section 트리를 재생성(idempotent). 통계 dict 반환."""
+    nodes = build_hier_tree(source_text)
+    if not nodes:
+        return {"doc_id": doc_id, "nodes": 0, "leaves": 0, "skipped": "empty"}
+
+    # domain_category 결정 (NOT NULL): legacy chunk 다수결 → fallback 'general'
+    if domain_category is None:
+        domain_category = await session.scalar(text("""
+            SELECT domain_category FROM document_chunks WHERE doc_id=:d
+            GROUP BY domain_category ORDER BY count(*) DESC LIMIT 1"""), {"d": doc_id}) or "general"
+
+    # idempotency: 기존 hier 행 삭제
+    await session.execute(text(
+        "DELETE FROM document_chunks WHERE doc_id=:d AND source_type=:st AND chunker_version=:cv"),
+        {"d": doc_id, "st": SOURCE_TYPE, "cv": CHUNKER_VERSION})
+
+    base = (await session.scalar(text(
+        "SELECT COALESCE(MAX(chunk_index),-1)+1 FROM document_chunks WHERE doc_id=:d"), {"d": doc_id})) or 0
+
+    idx_to_dbid: dict[int, int] = {}
+    embedded = 0
+    for n in nodes:  # parent always precedes child in list order
+        parent_db = idx_to_dbid.get(n.parent_idx) if n.parent_idx is not None else None
+        emb_str = None
+        if n.is_leaf:
+            emb = await embed_leaf(n.text)
+            if emb:
+                emb_str = "[" + ",".join(repr(float(x)) for x in emb) + "]"
+                embedded += 1
+        chunk_type = "section_md" if n.is_leaf else "section_container"
+        db_id = await session.scalar(text("""
+            INSERT INTO document_chunks
+              (doc_id, chunk_index, chunk_type, section_title, heading_path, domain_category,
+               text, embedding, source_type, chunker_version, chunk_content_hash,
+               parent_id, level, node_type, is_leaf, in_corpus)
+            VALUES (:d, :ci, :ct, :stt, :hp, :dc, :tx,
+               cast(cast(:emb AS text) AS vector),
+               :src, :cv, :hash, :pid, :lvl, :nt, :leaf, false)
+            RETURNING id"""), {
+                "d": doc_id, "ci": base + n.idx, "ct": chunk_type,
+                "stt": n.section_title, "hp": n.heading_path, "dc": domain_category,
+                "tx": n.text, "emb": emb_str, "src": SOURCE_TYPE, "cv": CHUNKER_VERSION,
+                "hash": n.chunk_content_hash, "pid": parent_db, "lvl": n.level,
+                "nt": n.node_type, "leaf": n.is_leaf})
+        idx_to_dbid[n.idx] = db_id
+    await session.commit()
+
+    leaves = [n for n in nodes if n.is_leaf]
+    st = coverage_stats(source_text, nodes)
+    st.update({"doc_id": doc_id, "base_chunk_index": base, "embedded_leaves": embedded,
+               "embed_coverage": round(embedded / len(leaves), 4) if leaves else 0,
+               "domain_category": domain_category})
+    return st
diff --git a/migrations/284_drop_full_embedding_index.sql b/migrations/284_drop_full_embedding_index.sql
new file mode 100644
index 0000000..a3b749a
--- /dev/null
+++ b/migrations/284_drop_full_embedding_index.sql
@@ -0,0 +1,5 @@
+-- PR-DocSrv-Hierarchical-Decomposition-1 (c4): ivfflat 오염 fix 1/2.
+-- 기존 full ivfflat(idx_chunks_embedding)은 in_corpus=false hier leaf 벡터까지 포함 →
+-- 근사 검색이 비활성 벡터에 오염됨(corpus_chunks 결과 필터해도 근사 이웃 셋이 흔들림).
+-- partial index(WHERE in_corpus=true)로 교체 위해 먼저 drop. (다음 285 에서 재생성)
+DROP INDEX IF EXISTS idx_chunks_embedding;
diff --git a/migrations/285_create_partial_embedding_index.sql b/migrations/285_create_partial_embedding_index.sql
new file mode 100644
index 0000000..9f13a3b
--- /dev/null
+++ b/migrations/285_create_partial_embedding_index.sql
@@ -0,0 +1,7 @@
+-- PR-DocSrv-Hierarchical-Decomposition-1 (c4): ivfflat 오염 fix 2/2.
+-- partial ivfflat — in_corpus=true 벡터만 색인 → in_corpus=false(비활성 hier leaf)는
+-- 검색 인덱스에 부재 = 검색 무영향이 인덱스 레벨에서 보장. replace 시 in_corpus 토글로 자동 편입/제외.
+-- corpus_chunks 쿼리(WHERE in_corpus=true)가 이 partial index 사용.
+CREATE INDEX IF NOT EXISTS idx_chunks_embedding ON document_chunks
+  USING ivfflat (embedding vector_cosine_ops) WITH (lists = '100')
+  WHERE in_corpus = true;