feat: 검색 전면 개편 — 필드별 가중치 + 벡터 합산 + match reason

검색 대상: title > ai_tags > user_note > ai_summary > extracted_text
- 필드별 가중치: title(3.0), tags(2.5), note(2.0), summary(1.5), text(1.0)
- 벡터 검색: 별도 쿼리로 분리, 결과 합산 (asyncpg 충돌 방지)
- match_reason: 어떤 필드에서 매칭됐는지 반환
- 중복 제거 + 점수 합산

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/api/search.py

@@ -1,4 +1,4 @@
-"""하이브리드 검색 API — FTS + 트리그램 + 벡터"""
+"""하이브리드 검색 API — FTS + ILIKE + 벡터 (필드별 가중치)"""
 
 from typing import Annotated
 
@@ -14,11 +14,6 @@ from models.user import User
 
 router = APIRouter()
 
-# 가중치 (초기값, 튜닝 가능)
-W_FTS = 0.4
-W_TRGM = 0.2
-W_VECTOR = 0.4
-
 
 class SearchResult(BaseModel):
     id: int
@@ -28,6 +23,7 @@ class SearchResult(BaseModel):
     file_format: str
     score: float
     snippet: str | None
+    match_reason: str | None = None
 
 
 class SearchResponse(BaseModel):
@@ -45,22 +41,16 @@ async def search(
     mode: str = Query("hybrid", pattern="^(fts|trgm|vector|hybrid)$"),
     limit: int = Query(20, ge=1, le=100),
 ):
-    """문서 검색
-
-    mode:
-    - fts: PostgreSQL 전문검색 (GIN 인덱스)
-    - trgm: 트리그램 부분매칭 (한국어 지원)
-    - vector: 벡터 유사도 검색 (의미검색)
-    - hybrid: FTS + 트리그램 + 벡터 결합 (기본)
-    """
-    if mode == "fts":
-        results = await _search_fts(session, q, limit)
-    elif mode == "trgm":
-        results = await _search_trgm(session, q, limit)
-    elif mode == "vector":
+    """문서 검색 — FTS + ILIKE + 벡터 결합"""
+    if mode == "vector":
         results = await _search_vector(session, q, limit)
     else:
-        results = await _search_hybrid(session, q, limit)
+        results = await _search_text(session, q, limit)
+
+        # hybrid: 벡터 결과도 합산
+        if mode == "hybrid":
+            vector_results = await _search_vector(session, q, limit)
+            results = _merge_results(results, vector_results, limit)
 
     return SearchResponse(
         results=results,
@@ -70,68 +60,69 @@ async def search(
     )
 
 
-async def _search_fts(session: AsyncSession, query: str, limit: int) -> list[SearchResult]:
-    """PostgreSQL 전문검색 (GIN 인덱스)"""
-    # simple 설정으로 한국어 토큰화 없이 공백 기반 분리
+async def _search_text(session: AsyncSession, query: str, limit: int) -> list[SearchResult]:
+    """FTS + ILIKE — 필드별 가중치 적용"""
     result = await session.execute(
         text("""
             SELECT id, title, ai_domain, ai_summary, file_format,
-                   ts_rank(
-                       to_tsvector('simple', coalesce(title, '') || ' ' || coalesce(extracted_text, '')),
-                       plainto_tsquery('simple', :query)
+                   left(extracted_text, 200) AS snippet,
+                   (
+                       -- title 매칭 (가중치 최고)
+                       CASE WHEN coalesce(title, '') ILIKE '%%' || :q || '%%' THEN 3.0 ELSE 0 END
+                       -- ai_tags 매칭 (가중치 높음)
+                       + CASE WHEN coalesce(ai_tags::text, '') ILIKE '%%' || :q || '%%' THEN 2.5 ELSE 0 END
+                       -- user_note 매칭 (가중치 높음)
+                       + CASE WHEN coalesce(user_note, '') ILIKE '%%' || :q || '%%' THEN 2.0 ELSE 0 END
+                       -- ai_summary 매칭 (가중치 중상)
+                       + CASE WHEN coalesce(ai_summary, '') ILIKE '%%' || :q || '%%' THEN 1.5 ELSE 0 END
+                       -- extracted_text 매칭 (가중치 중간)
+                       + CASE WHEN coalesce(extracted_text, '') ILIKE '%%' || :q || '%%' THEN 1.0 ELSE 0 END
+                       -- FTS 점수 (보너스)
+                       + coalesce(ts_rank(
+                           to_tsvector('simple', coalesce(title, '') || ' ' || coalesce(extracted_text, '')),
+                           plainto_tsquery('simple', :q)
+                       ), 0) * 2.0
                    ) AS score,
-                   left(extracted_text, 200) AS snippet
+                   -- match reason
+                   CASE
+                       WHEN coalesce(title, '') ILIKE '%%' || :q || '%%' THEN 'title'
+                       WHEN coalesce(ai_tags::text, '') ILIKE '%%' || :q || '%%' THEN 'tags'
+                       WHEN coalesce(user_note, '') ILIKE '%%' || :q || '%%' THEN 'note'
+                       WHEN coalesce(ai_summary, '') ILIKE '%%' || :q || '%%' THEN 'summary'
+                       WHEN coalesce(extracted_text, '') ILIKE '%%' || :q || '%%' THEN 'content'
+                       ELSE 'fts'
+                   END AS match_reason
             FROM documents
-            WHERE to_tsvector('simple', coalesce(title, '') || ' ' || coalesce(extracted_text, ''))
-                  @@ plainto_tsquery('simple', :query)
+            WHERE coalesce(title, '') ILIKE '%%' || :q || '%%'
+               OR coalesce(ai_tags::text, '') ILIKE '%%' || :q || '%%'
+               OR coalesce(user_note, '') ILIKE '%%' || :q || '%%'
+               OR coalesce(ai_summary, '') ILIKE '%%' || :q || '%%'
+               OR coalesce(extracted_text, '') ILIKE '%%' || :q || '%%'
+               OR to_tsvector('simple', coalesce(title, '') || ' ' || coalesce(extracted_text, ''))
+                  @@ plainto_tsquery('simple', :q)
             ORDER BY score DESC
             LIMIT :limit
         """),
-        {"query": query, "limit": limit},
-    )
-    return [SearchResult(**row._mapping) for row in result]
-
-
-async def _search_trgm(session: AsyncSession, query: str, limit: int) -> list[SearchResult]:
-    """트리그램 부분매칭 + ILIKE fallback (한국어 지원)"""
-    # threshold 낮춰서 한국어 매칭 향상
-    await session.execute(text("SET pg_trgm.similarity_threshold = 0.1"))
-    result = await session.execute(
-        text("""
-            SELECT id, title, ai_domain, ai_summary, file_format,
-                   GREATEST(
-                       similarity(coalesce(title, '') || ' ' || coalesce(extracted_text, ''), :query),
-                       CASE WHEN (coalesce(title, '') || ' ' || coalesce(extracted_text, '')) ILIKE '%%' || :query || '%%'
-                            THEN 0.5 ELSE 0 END
-                   ) AS score,
-                   left(extracted_text, 200) AS snippet
-            FROM documents
-            WHERE (coalesce(title, '') || ' ' || coalesce(extracted_text, '')) %% :query
-               OR (coalesce(title, '') || ' ' || coalesce(extracted_text, '')) ILIKE '%%' || :query || '%%'
-            ORDER BY score DESC
-            LIMIT :limit
-        """),
-        {"query": query, "limit": limit},
+        {"q": query, "limit": limit},
     )
     return [SearchResult(**row._mapping) for row in result]
 
 
 async def _search_vector(session: AsyncSession, query: str, limit: int) -> list[SearchResult]:
     """벡터 유사도 검색 (코사인 거리)"""
-    client = AIClient()
     try:
+        client = AIClient()
         query_embedding = await client.embed(query)
-    except Exception:
-        return []  # GPU 서버 불가 시 빈 결과
-    finally:
         await client.close()
+    except Exception:
+        return []
 
-    # pgvector 코사인 거리 (0=동일, 2=반대)
     result = await session.execute(
         text("""
             SELECT id, title, ai_domain, ai_summary, file_format,
                    (1 - (embedding <=> :embedding::vector)) AS score,
-                   left(extracted_text, 200) AS snippet
+                   left(extracted_text, 200) AS snippet,
+                   'vector' AS match_reason
             FROM documents
             WHERE embedding IS NOT NULL
             ORDER BY embedding <=> :embedding::vector
@@ -142,28 +133,33 @@ async def _search_vector(session: AsyncSession, query: str, limit: int) -> list[
     return [SearchResult(**row._mapping) for row in result]
 
 
-async def _search_hybrid(session: AsyncSession, query: str, limit: int) -> list[SearchResult]:
-    """하이브리드 검색 — FTS + ILIKE (안정적 한국어 지원)"""
-    result = await session.execute(
-        text("""
-            SELECT id, title, ai_domain, ai_summary, file_format,
-                   GREATEST(
-                       coalesce(ts_rank(
-                           to_tsvector('simple', coalesce(title, '') || ' ' || coalesce(extracted_text, '')),
-                           plainto_tsquery('simple', :query)
-                       ), 0),
-                       CASE WHEN (coalesce(title, '') || ' ' || coalesce(extracted_text, ''))
-                            ILIKE '%%' || :query || '%%' THEN 0.5 ELSE 0 END
-                   ) AS score,
-                   left(extracted_text, 200) AS snippet
-            FROM documents
-            WHERE to_tsvector('simple', coalesce(title, '') || ' ' || coalesce(extracted_text, ''))
-                  @@ plainto_tsquery('simple', :query)
-               OR (coalesce(title, '') || ' ' || coalesce(extracted_text, ''))
-                  ILIKE '%%' || :query || '%%'
-            ORDER BY score DESC
-            LIMIT :limit
-        """),
-        {"query": query, "limit": limit},
-    )
-    return [SearchResult(**row._mapping) for row in result]
+def _merge_results(
+    text_results: list[SearchResult],
+    vector_results: list[SearchResult],
+    limit: int,
+) -> list[SearchResult]:
+    """텍스트 + 벡터 결과 합산 (중복 제거, 점수 합산)"""
+    merged: dict[int, SearchResult] = {}
+
+    for r in text_results:
+        merged[r.id] = r
+
+    for r in vector_results:
+        if r.id in merged:
+            # 이미 텍스트로 잡힌 문서 — 벡터 점수 가산
+            existing = merged[r.id]
+            merged[r.id] = SearchResult(
+                id=existing.id,
+                title=existing.title,
+                ai_domain=existing.ai_domain,
+                ai_summary=existing.ai_summary,
+                file_format=existing.file_format,
+                score=existing.score + r.score * 0.5,
+                snippet=existing.snippet,
+                match_reason=f"{existing.match_reason}+vector",
+            )
+        elif r.score > 0.3:  # 벡터 유사도 최소 threshold
+            merged[r.id] = r
+
+    results = sorted(merged.values(), key=lambda x: x.score, reverse=True)
+    return results[:limit]