fix(ledger): dcy-015 outbox 영속 오류 분류 + 백오프/dead-letter (BAT-019)

portfolio-hub 404(미등록 포트폴리오)가 retryable 로 분류되어 백오프·상한 없이
초당 영구 재시도되던 버그(issue #13, 실측 930회) 정정.

거버넌스: 전부 change-req (신규 REQ 없음, dcy-015 OQ-3; 백오프 env 는 REQ-019 흡수).
- REQ-017: 404/400/422 → LedgerPermanentError 분류 (409 conflict / 408·429·5xx·
  network retryable 불변). LedgerPort 에 permanent 타입 추가
- REQ-019: 영속 → 터미널 delivery_failed 즉시(재시도 0). retryable 지수 백오프
  +jitter+next_retry_at, max_attempts 초과 시 dead-letter delivery_failed.
  list_pending 이 백오프 행 스킵(head-of-line 보호). 마이그레이션 007(status enum
  +next_retry_at). 백오프 env(base/cap/max-attempts)
- REQ-018: 터미널/dead-letter WARN + WriterStats.delivery_failed 카운터 가시화
- REQ-020: runtime-flows/data-model/interface-contract 정합

단일 터미널 delivery_failed(permanent/dead-letter, last_outcome 로 사유 구분) —
conflict_blocked 패턴과 동형. dead-letter 는 운영자 재처리 가능 상태.

검증: 단위 311 passed/34 skipped, 인프라 게이트(PG+RabbitMQ) 345 passed, ruff clean.
신규 test_ledger_outbox_backoff + adapter/PG 테스트, 기존 retryable 백오프 정합.
BAT-019 release-candidate.

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

trex_core/adapters/persistence/postgresql.py

@@ -325,7 +325,7 @@ class _PgIntentRecord:
 _OUTBOX_COLUMNS = (
     "correlation_id, asset_id, order_id, execution_id, side, qty, price, "
     "fee, tax, executed_at, status, attempts, last_outcome, last_error, "
-    "created_at, updated_at"
+    "created_at, updated_at, next_retry_at"
 )
 
 
@@ -362,7 +362,9 @@ class PostgreSQLLedgerOutbox:
             with conn.cursor() as cur:
                 cur.execute(
                     f"SELECT {_OUTBOX_COLUMNS} FROM ledger_outbox "
-                    "WHERE status = 'pending' ORDER BY created_at LIMIT %s",
+                    "WHERE status = 'pending' "
+                    "AND (next_retry_at IS NULL OR next_retry_at <= now()) "
+                    "ORDER BY created_at LIMIT %s",
                     (limit,),
                 )
                 return [self._row_to_item(r) for r in cur.fetchall()]
@@ -383,6 +385,7 @@ class PostgreSQLLedgerOutbox:
         outcome: OutboxOutcome,
         *,
         error: Optional[str] = None,
+        next_retry_at: Optional[datetime] = None,
     ) -> LedgerWorkItem:
         with self._psycopg.connect(self._dsn, autocommit=False) as conn:
             with conn.cursor() as cur:
@@ -392,18 +395,24 @@ class PostgreSQLLedgerOutbox:
                 elif outcome is OutboxOutcome.CONFLICT_BLOCKED:
                     status_value = WorkItemStatus.CONFLICT_BLOCKED.value
                     attempts_delta = 1
+                elif outcome in (OutboxOutcome.PERMANENT_FAILURE, OutboxOutcome.DEAD_LETTERED):
+                    # dcy-015 / REQ-019: terminal delivery_failed (reason in last_outcome).
+                    status_value = WorkItemStatus.DELIVERY_FAILED.value
+                    attempts_delta = 1
                 elif outcome is OutboxOutcome.DUPLICATE_COMPLETED:
                     status_value = WorkItemStatus.COMPLETED.value
                     attempts_delta = 0
                 else:  # retryable
                     status_value = WorkItemStatus.PENDING.value
                     attempts_delta = 1
+                # next_retry_at only persists for a retryable backoff; cleared otherwise.
+                nra = next_retry_at if outcome is OutboxOutcome.RETRYABLE_FAILURE else None
                 cur.execute(
                     "UPDATE ledger_outbox SET status=%s, attempts=attempts+%s, "
-                    "last_outcome=%s, last_error=%s, updated_at=%s "
+                    "last_outcome=%s, last_error=%s, next_retry_at=%s, updated_at=%s "
                     "WHERE correlation_id=%s",
                     (
-                        status_value, attempts_delta, outcome.value, error,
+                        status_value, attempts_delta, outcome.value, error, nra,
                         datetime.now(tz=timezone.utc), correlation_id,
                     ),
                 )
@@ -429,4 +438,5 @@ class PostgreSQLLedgerOutbox:
             last_error=row[13],
             created_at=row[14],
             updated_at=row[15],
+            next_retry_at=row[16],
         )