feat(holdings): REQ-043 현재 보유 평단(WAC) read — GET /v1/portfolios/{id}/holdings/cost-basis (BAT-018, PR #14)

dcy-008(confirmed)/REQ-043(Approved)/BAT-018. trex-core dcy-034 FR-7 cold-start seed 의존. AC 11/11, QC PASS. worktree+PR 워크플로 첫 파일럿.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VHtM5Ws1HKCKQ4JGi6GRb5

app/api/v1_portfolios.py

@@ -3,6 +3,7 @@
 REQ-005, REQ-025~031: Portfolio CRUD, tags, comments.
 REQ-039: GET /v1/portfolios/{id}/trades — trade history with date filter.
 REQ-040: GET /v1/portfolios/{id}/pnl/realized — WAC realized PnL.
+REQ-043: GET /v1/portfolios/{id}/holdings/cost-basis — current holding WAC cost basis.
 """
 
 from __future__ import annotations
@@ -16,7 +17,7 @@ from fastapi import APIRouter, Depends, HTTPException, Query, Response, status
 
 from app.core.auth import AuthContext, Permission, require_read, require_trade_write
 from app.domain.models import Portfolio, PortfolioComment
-from app.domain.pnl import calculate_realized_pnl
+from app.domain.pnl import calculate_current_wac, calculate_realized_pnl
 from app.repositories.factory import get_portfolio_repository_from_settings
 from app.schemas.v1 import (
     LedgerTradeRequest,
@@ -30,6 +31,7 @@ from app.schemas.v1 import (
     PortfolioListResponse,
     PortfolioTagListResponse,
     PortfolioUpdateRequest,
+    HoldingsCostBasisResponse,
     RealizedPnlItem,
     RealizedPnlResponse,
     TagApplyRequest,
@@ -794,3 +796,90 @@ def get_realized_pnl(
         cost_basis_from=result.cost_basis_from,
         data_completeness_warning=result.data_completeness_warning,
     )
+
+
+# ---------------------------------------------------------------------------
+# GET /v1/portfolios/{portfolio_id}/holdings/cost-basis  — REQ-043
+# ---------------------------------------------------------------------------
+
+@router.get("/{portfolio_id}/holdings/cost-basis", response_model=HoldingsCostBasisResponse)
+def get_holdings_cost_basis(
+    portfolio_id: str,
+    auth: AuthContext = Depends(require_read),
+) -> HoldingsCostBasisResponse:
+    """현재 보유 평단(WAC) 조회 — 미매도 보유분의 cost basis (REQ-043).
+
+    - service token: daemon_id == portfolio.managed_by_daemon_id 일치 시만 허용 (불일치/null → 403).
+    - user token: 소유자 또는 admin만 허용 (비소유자 → 403).
+    - 존재하지 않는 portfolio_id → 404.
+    - 보유수량 0인 경우 → 200 + current_quantity=0, cost_basis_per_unit=null, total_cost_basis=null.
+    """
+    repo = _get_repo()
+    try:
+        # Fetch portfolio (existence check)
+        try:
+            portfolio = repo.get(portfolio_id)
+        except ValueError:
+            raise HTTPException(
+                status_code=status.HTTP_404_NOT_FOUND,
+                detail=f"portfolio를 찾을 수 없습니다: {portfolio_id}",
+            )
+
+        # Ownership / scope check
+        if auth.token_type == "service":
+            # daemon scope: daemon_id must match managed_by_daemon_id
+            if portfolio.managed_by_daemon_id is None:
+                raise HTTPException(
+                    status_code=status.HTTP_403_FORBIDDEN,
+                    detail="daemon 미배정 portfolio에 daemon 접근 불가",
+                )
+            if auth.daemon_id is None or auth.daemon_id != portfolio.managed_by_daemon_id:
+                raise HTTPException(
+                    status_code=status.HTTP_403_FORBIDDEN,
+                    detail="Token daemon does not match portfolio daemon assignment",
+                )
+        else:
+            # user/admin token: non-admin must own the portfolio
+            if auth.permission != Permission.ADMIN and portfolio.owner_user_id != auth.user_id:
+                raise HTTPException(
+                    status_code=status.HTTP_403_FORBIDDEN,
+                    detail="Portfolio ownership mismatch",
+                )
+
+        # Fetch all ledger history for WAC replay
+        ledger_entries = repo.get_all_trades_for_pnl(portfolio_id, symbol=None)
+    except HTTPException:
+        raise
+    finally:
+        _close_repo(repo)
+
+    # Build rows for domain function
+    rows = [
+        {
+            "side": e.side,
+            "quantity": e.quantity,
+            "price": e.price,
+            "executed_at": e.executed_at,
+        }
+        for e in ledger_entries
+    ]
+
+    wac_result = calculate_current_wac(rows)
+
+    current_quantity = portfolio.asset_quantity
+    cost_basis_per_unit = wac_result.current_wac if current_quantity > 0 else None
+    total_cost_basis = (
+        cost_basis_per_unit * current_quantity
+        if cost_basis_per_unit is not None and current_quantity > 0
+        else None
+    )
+
+    return HoldingsCostBasisResponse(
+        portfolio_id=portfolio_id,
+        symbol=portfolio.symbol,
+        current_quantity=current_quantity,
+        cost_basis_per_unit=cost_basis_per_unit,
+        total_cost_basis=total_cost_basis,
+        cost_basis_from=wac_result.cost_basis_from,
+        data_completeness_warning=wac_result.data_completeness_warning,
+    )