feat(ledger): dcy-018 option D cash/position write-back + 추정 현금 (BAT-023)

ledger write 응답의 portfolio-hub 권위 cash/quantity 를 스냅샷에 write-back 해
매수/매도 직후 "수량 live·현금 stale" 비대칭 제거(option D 활성화). portfolio-hub#8
(*_after 응답) 동작 중 확인으로 그간 deferred 됐던 REQ-030 을 닫음.

거버넌스: 전부 change-req (신규 REQ 없음, dcy-018 OQ-3 a).
- REQ-017: record_trade → LedgerWriteOutcome{result, cash_balance_after,
  asset_quantity_after}. 어댑터가 응답 root flat *_after 파싱(new+duplicate, 누락 None)
- REQ-019: LedgerWriter 에 SnapshotStore 주입 → new+duplicate write-back
  (best-effort, *_after 절대값이라 멱등). LedgerOutbox.pending_cash_delta()
- REQ-029: 추정 현금 오버레이(_apply_cash_estimate, cash_estimated 라벨, OQ-4 i)
  + 슬롯 오버레이 유지(OQ-1 B). 미정산 outbox delta 기반, write-back 수렴
- REQ-030: option D 활성화 → Approved→Implemented

best-effort 격리(NFR-1): write-back/추정 실패가 ledger 멱등·청산 무차단.
배치 번호: 동시 커밋된 BAT-022(slot-state, dcy-016)와 충돌해 BAT-023 으로 배정.

검증: 단위 350 passed/35 skipped, 인프라 게이트(PG+RabbitMQ) 385 passed, ruff clean.
신규 test_ledger_option_d + adapter/PG 테스트. BAT-023 release-candidate.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

trex_core/adapters/ledger/in_memory.py

@@ -8,6 +8,7 @@ from trex_core.application.ledger_port import (
     LedgerPermanentError,
     LedgerRetryableError,
     LedgerTrade,
+    LedgerWriteOutcome,
     LedgerWriteResult,
 )
 
@@ -32,6 +33,8 @@ class InMemoryLedger:
         fail_n_then_succeed: int = 0,
         conflict_executions: set[str] | None = None,
         permanent_executions: set[str] | None = None,
+        cash_after: float | None = None,
+        quantity_after: float | None = None,
     ) -> None:
         self._trades: dict[str, LedgerTrade] = {}
         self._order: list[LedgerTrade] = []
@@ -39,8 +42,12 @@ class InMemoryLedger:
         self._fail_remaining = fail_n_then_succeed
         self._conflicts = set(conflict_executions or set())
         self._permanent = set(permanent_executions or set())
+        # dcy-018: optional authoritative cash/quantity returned on the outcome
+        # (simulates portfolio-hub#8 option D response). None => write-back skip.
+        self._cash_after = cash_after
+        self._quantity_after = quantity_after
 
-    def record_trade(self, trade: LedgerTrade) -> LedgerWriteResult:
+    def record_trade(self, trade: LedgerTrade) -> LedgerWriteOutcome:
         with self._lock:
             if trade.execution_id in self._conflicts:
                 raise LedgerConflictError(
@@ -55,10 +62,16 @@ class InMemoryLedger:
                 raise LedgerRetryableError("simulated transient failure")
             if trade.execution_id in self._trades:
                 # idempotent: same execution_id => no new entry, report dedup.
-                return LedgerWriteResult.DUPLICATE_OK
-            self._trades[trade.execution_id] = trade
-            self._order.append(trade)
-            return LedgerWriteResult.NEW
+                result = LedgerWriteResult.DUPLICATE_OK
+            else:
+                self._trades[trade.execution_id] = trade
+                self._order.append(trade)
+                result = LedgerWriteResult.NEW
+            return LedgerWriteOutcome(
+                result=result,
+                cash_balance_after=self._cash_after,
+                asset_quantity_after=self._quantity_after,
+            )
 
     # --- introspection for tests ---
     def trades(self) -> list[LedgerTrade]:

trex_core/adapters/ledger/portfolio_hub.py

@@ -26,9 +26,20 @@ from trex_core.application.ledger_port import (
     LedgerPermanentError,
     LedgerRetryableError,
     LedgerTrade,
+    LedgerWriteOutcome,
     LedgerWriteResult,
 )
 
+
+def _opt_num(v):
+    """Parse an optional numeric (cash/quantity) field; None if absent/invalid."""
+    if v is None:
+        return None
+    try:
+        return float(v)
+    except (TypeError, ValueError):
+        return None
+
 # dcy-015 / REQ-017: client errors that retrying cannot resolve.
 _PERMANENT_STATUS = frozenset({400, 404, 422})
 
@@ -75,7 +86,7 @@ class PortfolioHubLedger:
         return httpx.post(url, json=json, headers=self._headers(),
                           timeout=self._timeout)
 
-    def record_trade(self, trade: LedgerTrade) -> LedgerWriteResult:
+    def record_trade(self, trade: LedgerTrade) -> LedgerWriteOutcome:
         url = f"{self._base_url}/v1/portfolios/{trade.asset_id}/ledger/trades"
         try:
             resp = self._post(url, json=self._payload(trade))
@@ -89,9 +100,19 @@ class PortfolioHubLedger:
                 body = resp.json() if resp.content else {}
             except ValueError:
                 body = {}
-            if isinstance(body, dict) and body.get("duplicate") is True:
-                return LedgerWriteResult.DUPLICATE_OK
-            return LedgerWriteResult.NEW
+            if not isinstance(body, dict):
+                body = {}
+            result = (
+                LedgerWriteResult.DUPLICATE_OK if body.get("duplicate") is True
+                else LedgerWriteResult.NEW
+            )
+            # dcy-018 / REQ-017 (option D, portfolio-hub#8): root flat authoritative
+            # cash/quantity after the write — present on new(201) + duplicate(200).
+            return LedgerWriteOutcome(
+                result=result,
+                cash_balance_after=_opt_num(body.get("cash_balance_after")),
+                asset_quantity_after=_opt_num(body.get("asset_quantity_after")),
+            )
         if resp.status_code == 409:
             raise LedgerConflictError(
                 f"portfolio-hub 409 conflict for execution_id={trade.execution_id}: "