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>

tests/adapters/ledger/test_portfolio_hub_ledger.py

@@ -10,6 +10,7 @@ import pytest
 from trex_core.adapters.ledger.portfolio_hub import PortfolioHubLedger
 from trex_core.application.ledger_port import (
     LedgerConflictError,
+    LedgerPermanentError,
     LedgerRetryableError,
     LedgerTrade,
 )
@@ -76,3 +77,24 @@ def test_network_error_is_retryable():
     adapter = PortfolioHubLedger("https://portfolio-hub.test", client=_client(handler))
     with pytest.raises(LedgerRetryableError):
         adapter.record_trade(_trade())
+
+
+@pytest.mark.parametrize("status", [404, 400, 422])
+def test_client_errors_are_permanent(status):
+    """dcy-015 / REQ-017: 404/400/422 won't be fixed by retrying → permanent."""
+    def handler(request: httpx.Request) -> httpx.Response:
+        return httpx.Response(status, text='{"error":"portfolio not found"}')
+
+    adapter = PortfolioHubLedger("https://portfolio-hub.test", client=_client(handler))
+    with pytest.raises(LedgerPermanentError):
+        adapter.record_trade(_trade())
+
+
+def test_429_stays_retryable():
+    """dcy-015 / REQ-017: rate-limit is transient → retryable (not permanent)."""
+    def handler(request: httpx.Request) -> httpx.Response:
+        return httpx.Response(429, text="slow down")
+
+    adapter = PortfolioHubLedger("https://portfolio-hub.test", client=_client(handler))
+    with pytest.raises(LedgerRetryableError):
+        adapter.record_trade(_trade())