fix(admin): propagate cache errors in FlushTaskExecutionLog

缓存故障（非 ErrCacheMiss）不再被静默吞掉：上抛包装错误，避免缓冲任务日志丢失并误报持久化成功；
ErrCacheMiss 仍视为无日志的正常路径。附 3 个回归测试（故障/未命中/持久化+清理）。
lint_issues 34→33 (nilerr 清零)

backend/plugins/domain/admin/repository.go

@@ -4,6 +4,7 @@
 package admin
 
 import (
+	"Wavelet/core/contracts"
 	"Wavelet/pkg/cache/ram"
 	"Wavelet/pkg/idgen"
 	"Wavelet/pkg/util"
@@ -502,7 +503,15 @@ func FlushTaskExecutionLog(ctx context.Context, taskID string) error {
 
 	key := taskExecutionLogRedisKey(taskID)
 	var logText string
-	if err := cacheSvc.Get(ctx, key, &logText); err != nil || logText == "" {
+	if err := cacheSvc.Get(ctx, key, &logText); err != nil {
+		// 缓存未命中属于正常情况（任务无输出），其余错误必须上抛，
+		// 否则缓冲日志会被静默丢弃并误报持久化成功。
+		if !errors.Is(err, contracts.ErrCacheMiss) {
+			return fmt.Errorf("load buffered task execution log: %w", err)
+		}
+		return nil
+	}
+	if logText == "" {
 		return nil
 	}
 

backend/plugins/domain/admin/repository_flush_log_test.go

@@ -0,0 +1,113 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package admin
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/alicebob/miniredis/v2"
+	"github.com/redis/go-redis/v9"
+	"github.com/redis/go-redis/v9/maintnotifications"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/glebarez/sqlite"
+	"gorm.io/gorm"
+
+	"Wavelet/core"
+	"Wavelet/core/contracts"
+	cacheplugin "Wavelet/plugins/infra/cache"
+)
+
+// stubDBService 用内存 SQLite 满足 DBService 契约，隔离外部依赖。
+type stubDBService struct{ db *gorm.DB }
+
+func (s stubDBService) GORM() *gorm.DB { return s.db }
+
+func (s stubDBService) DB(context.Context) *gorm.DB { return s.db }
+
+func (s stubDBService) Named(string) *gorm.DB { return s.db }
+
+// newFlushLogTestCache 构建真实多层缓存服务并注入 admin 插件上下文。
+func newFlushLogTestCache(t *testing.T) (contracts.CacheService, *miniredis.Miniredis, func()) {
+	t.Helper()
+	mr, err := miniredis.Run()
+	require.NoError(t, err)
+	rdb := redis.NewClient(&redis.Options{Addr: mr.Addr(), MaintNotificationsConfig: &maintnotifications.Config{Mode: maintnotifications.ModeDisabled}})
+
+	p := cacheplugin.New(cacheplugin.WithRedis(rdb), cacheplugin.WithRAMCapacity(64))
+	ctx := core.NewContext(context.Background())
+	require.NoError(t, p.Apply(ctx))
+	svc, err := core.Inject[contracts.CacheService](ctx)
+	require.NoError(t, err)
+
+	prev := cacheService
+	SetCacheService(svc)
+	cleanup := func() {
+		SetCacheService(prev)
+		_ = rdb.Close()
+		mr.Close()
+	}
+	return svc, mr, cleanup
+}
+
+// TestFlushTaskExecutionLogPropagatesCacheError 回归：缓存读取失败（非未命中）时，
+// FlushTaskExecutionLog 必须返回错误而不是静默吞掉日志并误报成功（nilerr 修复）。
+func TestFlushTaskExecutionLogPropagatesCacheError(t *testing.T) {
+	_, mr, cleanup := newFlushLogTestCache(t)
+	defer cleanup()
+
+	ctx := context.Background()
+	const taskID = "flush-err-task"
+
+	// 先缓冲一行日志
+	require.NoError(t, AppendTaskExecutionLog(ctx, taskID, "step-1 ok"))
+
+	// 关闭 miniredis 模拟缓存基础设施故障（读取出错而非未命中）
+	mr.Close()
+
+	err := FlushTaskExecutionLog(ctx, taskID)
+	assert.Error(t, err, "缓存故障时必须返回错误，防止缓冲日志被静默丢弃")
+}
+
+// TestFlushTaskExecutionLogCacheMissIsNoop 回归：任务无缓冲日志（未命中）时应为空操作成功。
+func TestFlushTaskExecutionLogCacheMissIsNoop(t *testing.T) {
+	_, _, cleanup := newFlushLogTestCache(t)
+	defer cleanup()
+
+	ctx := context.Background()
+	assert.NoError(t, FlushTaskExecutionLog(ctx, "missing-task"))
+}
+
+// TestFlushTaskExecutionLogPersistsAndClears 验证正常路径：缓冲日志写入执行记录后清理缓存。
+func TestFlushTaskExecutionLogPersistsAndClears(t *testing.T) {
+	svc, _, cleanup := newFlushLogTestCache(t)
+	defer cleanup()
+
+	ctx := context.Background()
+	const taskID = "flush-ok-task"
+	require.NoError(t, AppendTaskExecutionLog(ctx, taskID, "done"))
+
+	sqliteDB, err := gorm.Open(sqlite.Open(":memory:"), &gorm.Config{})
+	require.NoError(t, err)
+	require.NoError(t, sqliteDB.AutoMigrate(&TaskExecution{}))
+	SetDBService(stubDBService{db: sqliteDB})
+	defer SetDBService(nil)
+	gormDB := sqliteDB
+	exec := &TaskExecution{TaskID: taskID, TaskType: "upload:test", TaskName: "t", Status: TaskExecutionStatusSucceeded}
+	require.NoError(t, gormDB.Create(exec).Error)
+
+	require.NoError(t, FlushTaskExecutionLog(ctx, taskID))
+
+	var got TaskExecution
+	require.NoError(t, gormDB.First(&got, exec.ID).Error)
+	assert.Contains(t, got.Log, "done")
+
+	// 缓存中的缓冲日志应已被清理
+	var buf string
+	err = svc.Get(ctx, taskExecutionLogRedisKey(taskID), &buf)
+	assert.True(t, errors.Is(err, contracts.ErrCacheMiss), "flush 后缓存应清空, got %v", err)
+}