避免联通实名回调因内部长度限制永久失效

将实名事件身份收敛为受 Outbox 上限约束的稳定摘要，并允许相同 CUCC 回调原子认领失败终态后重试。

Constraint: 运营商回调固定返回成功，公共 Outbox event_id 上限为 64 字符

Rejected: 扩大数据库字段 | 根因是不受控事件 ID，且无法解决旧 failed 回调被吞

Confidence: high

Scope-risk: moderate

Directive: 新增稳定事件 ID 时必须服从持久化长度上限；失败回调恢复必须使用条件更新原子认领

Tested: gofmt；git diff --cached --check

Not-tested: 按用户要求未运行自动化测试、构建或测试环境重放

internal/application/cardobservation/apply.go

@@ -3,6 +3,8 @@ package cardobservation
 
 import (
 	"context"
+	"crypto/sha256"
+	"encoding/hex"
 	"strconv"
 	"time"
 
@@ -98,7 +100,7 @@ func (s *Service) ApplyCardObservation(ctx context.Context, observation domain.R
 			return errors.New(errors.CodeConflict, "卡实名状态已被其他请求更新")
 		}
 		if decision.StatusChanged {
-			eventID := "card-realname:" + strconv.FormatUint(uint64(card.ID), 10) + ":" + observation.Metadata.ObservationID + ":changed"
+			eventID := realnameChangedEventID(card.ID, observation.Metadata.ObservationID)
 			if err := s.eventWriter.AppendRealname(ctx, tx, RealnameChangedEvent{
 				EventID: eventID, CardID: card.ID, BeforeStatus: card.RealNameStatus, AfterStatus: decision.AfterStatus,
 				FirstVerified: decision.FirstVerified, ObservedAt: observation.Metadata.ObservedAt,
@@ -118,3 +120,10 @@ func (s *Service) ApplyCardObservation(ctx context.Context, observation domain.R
 	}
 	return decision, nil
 }
+
+func realnameChangedEventID(cardID uint, observationID string) string {
+	prefix := "card-realname:"
+	digest := sha256.Sum256([]byte(strconv.FormatUint(uint64(cardID), 10) + ":" + observationID + ":changed"))
+	// 使用稳定摘要保留幂等语义，同时严格服从公共 Outbox 的字段长度上限。
+	return prefix + hex.EncodeToString(digest[:])[:constants.OutboxEventIDMaxLength-len(prefix)]
+}