feat(study): 이론↔문제 브리지 (Stage B) — 개념별 정답률·약점 개념 지도

이론공부 B→A→C 의 B. 완성된 문제풀이에 이론 연결(약점 구동).
- 마이그 382 study_concept_links(개념 doc↔기출, FK 없음) + 백필 SQL(임베딩 코사인 top-k=10·threshold 0.62 → 2362링크·284개념·964문항)
- concept_links 서비스(related_questions·weakness_map 롤업) + GET /concepts/{id}/questions·/concepts/weakness-map(라우트 순서=weakness-map 먼저)
- 리더 관련기출 섹션(정답률·문항 stub→문항상세) + 홈 약점개념 위젯
- 적대리뷰 반영: Promise.all 격리(weakness-map 실패→코어 대시보드 블랙아웃 방지)·q.subject null 폴백. 백필=배포 후 트랜잭션 래핑 실행. 문제풀이 무접촉

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/api/study_concepts.py

@@ -15,6 +15,7 @@ from core.auth import get_current_user
 from core.database import get_session
 from models.user import User
 from services.study import concept_curriculum as cc
+from services.study import concept_links as cl
 
 router = APIRouter()
 
@@ -43,6 +44,20 @@ async def get_today_concepts(
     return await cc.today_concepts(session, user.id, topic_id, limit)
 
 
+@router.get("/concepts/weakness-map")
+async def get_weakness_map(
+    user: Annotated[User, Depends(get_current_user)],
+    session: Annotated[AsyncSession, Depends(get_session)],
+    topic_id: int = DEFAULT_TOPIC_ID,
+    limit: int = 12,
+):
+    """개념 약점 지도 — 링크된 기출 정답률로 약점 개념(정답률<60%) 우선(이론↔문제)."""
+    name = await cc._topic_name(session, topic_id)
+    if not name:
+        return {"weak": [], "weak_total": 0, "evaluated_total": 0}
+    return await cl.weakness_map(session, user.id, name, limit)
+
+
 @router.get("/concepts/{doc_id}")
 async def get_concept_detail(
     doc_id: int,
@@ -57,6 +72,17 @@ async def get_concept_detail(
     return detail
 
 
+@router.get("/concepts/{doc_id}/questions")
+async def get_concept_questions(
+    doc_id: int,
+    user: Annotated[User, Depends(get_current_user)],
+    session: Annotated[AsyncSession, Depends(get_session)],
+    limit: int = 20,
+):
+    """개념 관련 기출 + 내 정답률 (이론↔문제 브리지)."""
+    return await cl.related_questions(session, user.id, doc_id, limit)
+
+
 @router.post("/concepts/{doc_id}/read")
 async def post_concept_read(
     doc_id: int,

app/services/study/concept_links.py

@@ -0,0 +1,139 @@
+"""concept_links — 이론↔문제 브리지 롤업 (Stage B).
+
+study_concept_links(개념 doc ↔ 기출문항, 임베딩 코사인) + study_question_progress(내 풀이상태)를
+조인해 (a) 개념별 관련 기출 + 내 정답률(related_questions), (b) 개념 약점 지도(weakness_map) 산출.
+읽기 전용 집계 · LLM 0. 링크 적재는 scripts/concept_links_backfill.sql(임베딩) 배치.
+정답률 = 링크된 문항 중 progress.last_outcome 기준(attempted=풀이이력 보유, correct=최근정답).
+"""
+
+from __future__ import annotations
+
+from sqlalchemy import text
+from sqlalchemy.ext.asyncio import AsyncSession
+
+_ACCURACY_WEAK_PCT = 60  # 정답률 < 60% = 약점(attempted>0 일 때만)
+
+_AGG_SQL = text(
+    """
+    SELECT count(*) AS linked,
+           count(pr.study_question_id) FILTER (WHERE pr.last_outcome IS NOT NULL) AS attempted,
+           count(*) FILTER (WHERE pr.last_outcome = 'correct') AS correct
+    FROM study_concept_links l
+    LEFT JOIN study_question_progress pr
+      ON pr.study_question_id = l.question_id AND pr.user_id = :uid
+    WHERE l.concept_doc_id = :doc_id AND l.link_source = 'embedding'
+    """
+)
+
+_QROWS_SQL = text(
+    """
+    SELECT q.id AS id, q.subject AS subject, q.exam_round AS exam_round,
+           q.exam_question_number AS qnum, l.score AS score,
+           pr.last_outcome AS last_outcome, pr.review_stage AS review_stage
+    FROM study_concept_links l
+    JOIN study_questions q ON q.id = l.question_id AND q.deleted_at IS NULL AND q.is_active
+    LEFT JOIN study_question_progress pr
+      ON pr.study_question_id = q.id AND pr.user_id = :uid
+    WHERE l.concept_doc_id = :doc_id AND l.link_source = 'embedding'
+    ORDER BY l.score DESC
+    LIMIT :limit
+    """
+)
+
+_WEAKNESS_SQL = text(
+    """
+    SELECT d.id AS doc_id, d.title AS title,
+           split_part(replace(d.user_tags::text, '"', ''), '/', 3) AS subject,
+           count(l.id) AS linked,
+           count(pr.study_question_id) FILTER (WHERE pr.last_outcome IS NOT NULL) AS attempted,
+           count(*) FILTER (WHERE pr.last_outcome = 'correct') AS correct
+    FROM documents d
+    JOIN study_concept_links l ON l.concept_doc_id = d.id AND l.link_source = 'embedding'
+    LEFT JOIN study_question_progress pr
+      ON pr.study_question_id = l.question_id AND pr.user_id = :uid
+    WHERE d.user_tags::text LIKE :like AND d.deleted_at IS NULL
+    GROUP BY d.id, d.title, subject
+    """
+)
+
+
+async def related_questions(
+    session: AsyncSession, user_id: int, doc_id: int, limit: int = 20
+) -> dict:
+    """개념 doc 의 관련 기출 + 내 정답률(전체 링크 기준 집계 + 상위 N 표시용)."""
+    agg = (
+        await session.execute(_AGG_SQL, {"uid": user_id, "doc_id": doc_id})
+    ).mappings().first()
+    rows = (
+        await session.execute(
+            _QROWS_SQL, {"uid": user_id, "doc_id": doc_id, "limit": limit}
+        )
+    ).mappings().all()
+
+    linked = (agg["linked"] if agg else 0) or 0
+    attempted = (agg["attempted"] if agg else 0) or 0
+    correct = (agg["correct"] if agg else 0) or 0
+    accuracy = round(100 * correct / attempted) if attempted else None
+
+    return {
+        "linked": linked,
+        "attempted": attempted,
+        "correct": correct,
+        "accuracy": accuracy,
+        "questions": [
+            {
+                "id": r["id"],
+                "subject": r["subject"],
+                "exam_round": r["exam_round"],
+                "qnum": r["qnum"],
+                "score": round(r["score"], 3) if r["score"] is not None else None,
+                "last_outcome": r["last_outcome"],
+                "review_stage": r["review_stage"],
+            }
+            for r in rows
+        ],
+    }
+
+
+async def weakness_map(
+    session: AsyncSession, user_id: int, topic_name: str, limit: int = 12
+) -> dict:
+    """개념 약점 지도 — 링크된 기출 정답률로 개념 채색. 약점(attempted>0·정답률<60%) 우선 정렬."""
+    like = f"%@library/{topic_name}/%"
+    rows = (
+        await session.execute(_WEAKNESS_SQL, {"uid": user_id, "like": like})
+    ).mappings().all()
+
+    concepts = []
+    for r in rows:
+        attempted = r["attempted"] or 0
+        correct = r["correct"] or 0
+        accuracy = round(100 * correct / attempted) if attempted else None
+        if accuracy is None:
+            state = "unattempted"
+        elif accuracy < _ACCURACY_WEAK_PCT:
+            state = "weak"
+        else:
+            state = "ok"
+        concepts.append(
+            {
+                "doc_id": r["doc_id"],
+                "title": r["title"],
+                "subject": r["subject"],
+                "linked": r["linked"] or 0,
+                "attempted": attempted,
+                "accuracy": accuracy,
+                "state": state,
+            }
+        )
+
+    # 약점 우선(정답률 오름차순) → 미평가는 뒤로. 홈 위젯용 상위 N.
+    weak = sorted(
+        [c for c in concepts if c["state"] == "weak"],
+        key=lambda c: (c["accuracy"], -c["attempted"], c["doc_id"]),
+    )
+    return {
+        "weak": weak[:limit],
+        "weak_total": len(weak),
+        "evaluated_total": sum(1 for c in concepts if c["state"] != "unattempted"),
+    }