diff --git a/app/components/storage/SiteSyncCard.vue b/app/components/storage/SiteSyncCard.vue
index 3e9c9ef..08dd711 100644
--- a/app/components/storage/SiteSyncCard.vue
+++ b/app/components/storage/SiteSyncCard.vue
@@ -57,6 +57,11 @@ const fileProgress = computed(() => {
   }
 })
 const isPull = computed(() => direction.value === 'pull')
+const canAbandon = computed(() =>
+  !props.busy
+  && Boolean(props.resumableJob)
+  && (isPull.value || Boolean(token.value.trim()))
+)
 const directionSubtitle = computed(() => (
   isPull.value
     ? t('storage.backup.siteSyncPullSubtitle')
@@ -103,6 +108,19 @@ function resumeSync() {
   submit(true)
 }
 
+function abandonSync() {
+  if (!canAbandon.value || !props.resumableJob) return
+  if (!window.confirm(t('storage.backup.siteSyncAbandonConfirm'))) return
+  emit('sync', {
+    targetBaseUrl: targetBaseUrl.value.trim(),
+    token: token.value.trim(),
+    conflictMode: conflictMode.value,
+    direction: direction.value,
+    abandonJobId: props.resumableJob.id
+  })
+  token.value = ''
+}
+
 function setConflictMode(mode: 'skip' | 'overwrite') {
   conflictMode.value = mode
 }
@@ -171,6 +189,17 @@ function setDirection(value: SiteSyncDirection) {
         class="lg:col-start-3"
         @click="resumeSync"
       />
+      <UButton
+        v-if="resumableJob"
+        :label="t('storage.backup.siteSyncAbandon')"
+        icon="i-lucide-trash-2"
+        color="error"
+        variant="outline"
+        :loading="busy"
+        :disabled="!canAbandon"
+        class="lg:col-start-3"
+        @click="abandonSync"
+      />
     </div>
 
     <div class="mt-3 grid gap-3 sm:grid-cols-2">
diff --git a/app/composables/useBackup.ts b/app/composables/useBackup.ts
index 3ec3788..6a286a5 100644
--- a/app/composables/useBackup.ts
+++ b/app/composables/useBackup.ts
@@ -268,7 +268,12 @@ export function useBackup() {
       )
       await refreshJobsFirstPage()
       startPolling()
-      toast.add({ title: t('storage.backup.siteSyncStarted'), color: 'success' })
+      toast.add({
+        title: body.abandonJobId
+          ? t('storage.backup.siteSyncAbandoned')
+          : t('storage.backup.siteSyncStarted'),
+        color: 'success'
+      })
       return data.job
     } catch (error: unknown) {
       handleError(error, t('storage.backup.siteSyncFailed'))
diff --git a/app/types/backup.ts b/app/types/backup.ts
index 2ac71b6..c617419 100644
--- a/app/types/backup.ts
+++ b/app/types/backup.ts
@@ -59,4 +59,5 @@ export interface SiteSyncRequest {
   conflictMode: 'skip' | 'overwrite'
   direction: SiteSyncDirection
   resumeJobId?: string
+  abandonJobId?: string
 }
diff --git a/i18n/locales/en.json b/i18n/locales/en.json
index 761d4ff..cb2ce11 100644
--- a/i18n/locales/en.json
+++ b/i18n/locales/en.json
@@ -665,6 +665,9 @@
       "siteSyncSkip": "Skip existing",
       "siteSyncOverwrite": "Overwrite existing",
       "siteSyncResume": "Resume last sync",
+      "siteSyncAbandon": "Abandon and clean up",
+      "siteSyncAbandonConfirm": "Abandon this sync and delete partial objects created by it that are not yet referenced by a media record?",
+      "siteSyncAbandoned": "Sync abandoned and partial objects cleaned up",
       "siteSyncScanProgress": "Media scan progress",
       "siteSyncFileProgress": "Synced file count",
       "siteSyncStarted": "Site-to-site sync started",
diff --git a/i18n/locales/zh-CN.json b/i18n/locales/zh-CN.json
index 4cb395b..977c717 100644
--- a/i18n/locales/zh-CN.json
+++ b/i18n/locales/zh-CN.json
@@ -665,6 +665,9 @@
       "siteSyncSkip": "跳过已存在",
       "siteSyncOverwrite": "覆盖已存在",
       "siteSyncResume": "继续上次同步",
+      "siteSyncAbandon": "放弃并清理残留",
+      "siteSyncAbandonConfirm": "确定放弃这次同步吗？将删除本次同步新建但尚未归入媒体记录的残留对象。",
+      "siteSyncAbandoned": "同步已放弃，残留对象已清理",
       "siteSyncScanProgress": "媒体扫描进度",
       "siteSyncFileProgress": "已同步文件数量",
       "siteSyncStarted": "两站点同步任务已开始",
diff --git a/server/api/admin/site-sync.post.ts b/server/api/admin/site-sync.post.ts
index 669ddf7..ae5c114 100644
--- a/server/api/admin/site-sync.post.ts
+++ b/server/api/admin/site-sync.post.ts
@@ -5,6 +5,7 @@ import {
   resumeSiteSyncJob,
   startSiteSyncJob
 } from '../../utils/backup/runner'
+import { abandonSiteSyncJob } from '../../utils/site-sync/abandon'
 
 interface SiteSyncBody {
   targetBaseUrl?: string
@@ -12,6 +13,7 @@ interface SiteSyncBody {
   conflictMode?: 'skip' | 'overwrite'
   direction?: 'push' | 'pull'
   resumeJobId?: string
+  abandonJobId?: string
 }
 
 export default defineEventHandler(async (event) => {
@@ -22,11 +24,15 @@ export default defineEventHandler(async (event) => {
   const conflictMode = body?.conflictMode === 'skip' ? 'skip' : 'overwrite'
   const direction = body?.direction === 'pull' ? 'pull' : 'push'
 
-  if (!token) {
+  if (!token && !body?.abandonJobId) {
     createApiError(event, 'INVALID_REQUEST', '请输入目标站点管理员 API Token', 400)
   }
 
   try {
+    if (body?.abandonJobId) {
+      const job = await abandonSiteSyncJob(body.abandonJobId, token, user.id)
+      return { job: serializeBackupJob(job) }
+    }
     let job
     if (body?.resumeJobId) {
       job = resumeSiteSyncJob(body.resumeJobId, token, user.id)
@@ -54,6 +60,14 @@ export default defineEventHandler(async (event) => {
     if (error instanceof Error && error.message === 'SITE_SYNC_JOB_NOT_RESUMABLE') {
       createApiError(event, 'INVALID_REQUEST', '该同步任务无法继续', 400)
     }
+    if (body?.abandonJobId) {
+      createApiError(
+        event,
+        'INVALID_REQUEST',
+        error instanceof Error ? error.message : '放弃同步失败',
+        400
+      )
+    }
     throw error
   }
 })
diff --git a/server/api/site-sync/cleanup.post.ts b/server/api/site-sync/cleanup.post.ts
new file mode 100644
index 0000000..10fd834
--- /dev/null
+++ b/server/api/site-sync/cleanup.post.ts
@@ -0,0 +1,20 @@
+import { requireSiteSyncAuth } from '../../utils/access'
+import { createApiError } from '../../utils/api-error'
+import { cleanupSiteSyncJobArtifacts } from '../../utils/site-sync/artifacts'
+
+interface Body {
+  jobId?: string
+}
+
+export default defineEventHandler(async (event) => {
+  await requireSiteSyncAuth(event)
+  const body = await readBody<Body>(event).catch(() => null)
+  const jobId = body?.jobId?.trim() ?? ''
+  if (!jobId || jobId.length > 128) {
+    createApiError(event, 'INVALID_REQUEST', '缺少同步任务 ID', 400)
+  }
+  return {
+    success: true,
+    ...await cleanupSiteSyncJobArtifacts(jobId)
+  }
+})
diff --git a/server/api/site-sync/complete.post.ts b/server/api/site-sync/complete.post.ts
new file mode 100644
index 0000000..c2972ed
--- /dev/null
+++ b/server/api/site-sync/complete.post.ts
@@ -0,0 +1,21 @@
+import { requireSiteSyncAuth } from '../../utils/access'
+import { createApiError } from '../../utils/api-error'
+import { validateStorageKey } from '../../utils/image-key'
+import { completeSiteSyncMediaArtifacts } from '../../utils/site-sync/artifacts'
+
+interface Body {
+  jobId?: string
+  mediaKey?: string
+}
+
+export default defineEventHandler(async (event) => {
+  await requireSiteSyncAuth(event)
+  const body = await readBody<Body>(event).catch(() => null)
+  const jobId = body?.jobId?.trim() ?? ''
+  const mediaKey = body?.mediaKey?.trim() ?? ''
+  if (!jobId || jobId.length > 128 || !validateStorageKey(mediaKey)) {
+    createApiError(event, 'INVALID_REQUEST', '同步完成标记参数无效', 400)
+  }
+  completeSiteSyncMediaArtifacts(jobId, mediaKey)
+  return { success: true }
+})
diff --git a/server/api/site-sync/media.post.ts b/server/api/site-sync/media.post.ts
index 6f5a115..16cf32b 100644
--- a/server/api/site-sync/media.post.ts
+++ b/server/api/site-sync/media.post.ts
@@ -2,11 +2,13 @@ import { requireSiteSyncAuth } from '../../utils/access'
 import { createApiError } from '../../utils/api-error'
 import { validateStorageKey } from '../../utils/image-key'
 import { applySiteSyncMedia } from '../../utils/site-sync/apply'
+import { completeSiteSyncMediaArtifacts } from '../../utils/site-sync/artifacts'
 import type { SiteSyncMediaTransfer } from '../../utils/site-sync/protocol'
 
 interface Body {
   media?: SiteSyncMediaTransfer
   conflictMode?: 'skip' | 'overwrite'
+  jobId?: string
 }
 
 export default defineEventHandler(async (event) => {
@@ -18,7 +20,11 @@ export default defineEventHandler(async (event) => {
   }
   const conflictMode = body?.conflictMode === 'skip' ? 'skip' : 'overwrite'
   try {
-    return await applySiteSyncMedia(media, conflictMode, admin.id)
+    const result = await applySiteSyncMedia(media, conflictMode, admin.id)
+    if (body?.jobId) {
+      completeSiteSyncMediaArtifacts(body.jobId, media.key)
+    }
+    return result
   } catch (error) {
     const message = error instanceof Error ? error.message : '媒体同步失败'
     createApiError(event, 'INVALID_REQUEST', message, 400)
diff --git a/server/api/site-sync/object.post.ts b/server/api/site-sync/object.post.ts
index f386d3d..9faa5e7 100644
--- a/server/api/site-sync/object.post.ts
+++ b/server/api/site-sync/object.post.ts
@@ -5,6 +5,7 @@ import { MAX_VIDEO_FILE_SIZE } from '../../utils/constants'
 import { findUserByUsername } from '../../utils/db'
 import { validateStorageKey } from '../../utils/image-key'
 import { getActiveBackend } from '../../utils/storage/resolver'
+import { recordSiteSyncArtifact } from '../../utils/site-sync/artifacts'
 
 function field(form: Awaited<ReturnType<typeof readMultipartFormData>>, name: string): string {
   const part = form?.find(item => item.name === name)
@@ -30,6 +31,7 @@ export default defineEventHandler(async (event) => {
   if (conflictMode === 'skip' && await backend.head(key)) {
     return { success: true, skipped: true }
   }
+  const existedBefore = Boolean(await backend.head(key))
 
   const ownerUsername = field(form, 'ownerUsername')
   const owner = ownerUsername ? findUserByUsername(ownerUsername) : null
@@ -37,6 +39,18 @@ export default defineEventHandler(async (event) => {
     createApiError(event, 'INVALID_REQUEST', `目标站点缺少用户：${ownerUsername}`, 400)
   }
 
+  const jobId = field(form, 'jobId')
+  const mediaKey = field(form, 'mediaKey')
+  if (jobId && validateStorageKey(mediaKey)) {
+    recordSiteSyncArtifact({
+      jobId,
+      mediaKey,
+      key,
+      backendId: backend.id,
+      created: !existedBefore
+    })
+  }
+
   await backend.put(key, new Uint8Array(file.data), {
     originalName: field(form, 'originalName') || file.filename || key.split('/').pop() || 'file',
     uploadedAt: field(form, 'uploadedAt') || new Date().toISOString(),
diff --git a/server/plugins/startup.ts b/server/plugins/startup.ts
index fe1f79b..72a99b7 100644
--- a/server/plugins/startup.ts
+++ b/server/plugins/startup.ts
@@ -5,6 +5,9 @@ import { join } from 'node:path'
 import { runAutoDeleteCleanup } from '../utils/auto-delete'
 import { migrateLocalImagesToIndex, purgeOrphanImageIndexRows, reconcileLegacyImageKeys, repairLocalImageIndexMetadata } from '../utils/image-index'
 import { ensureDefaultBackends } from '../utils/storage-backends'
+import { cleanupLocalAtomicTempFiles } from '../utils/storage/local'
+import { cleanupExpiredSiteSyncArtifacts } from '../utils/site-sync/artifacts'
+import { recoverInterruptedBackupJobs } from '../utils/backup/jobs'
 import {
   cleanupTranscodedSources,
   killOrphanFfmpeg,
@@ -26,6 +29,37 @@ export default defineNitroPlugin(() => {
 
   ensureDefaultBackends()
 
+  try {
+    const interrupted = recoverInterruptedBackupJobs()
+    if (interrupted > 0) {
+      logInfo('已将异常退出时未完成的任务标记为失败', { interrupted })
+    }
+  } catch (error) {
+    logException('恢复异常退出的备份任务失败', error)
+  }
+
+  void (async () => {
+    try {
+      const removed = await cleanupLocalAtomicTempFiles()
+      if (removed > 0) {
+        logInfo('清理过期的原子写入临时文件', { removed })
+      }
+    } catch (error) {
+      logException('清理原子写入临时文件失败', error)
+    }
+  })()
+
+  void (async () => {
+    try {
+      const result = await cleanupExpiredSiteSyncArtifacts()
+      if (result.jobs > 0) {
+        logInfo('清理过期站点同步残留', result)
+      }
+    } catch (error) {
+      logException('清理站点同步残留失败', error)
+    }
+  })()
+
   /** 清理上次异常退出留下的转码临时目录 */
   void (async () => {
     try {
diff --git a/server/utils/backup/cancel-state.ts b/server/utils/backup/cancel-state.ts
new file mode 100644
index 0000000..48cd602
--- /dev/null
+++ b/server/utils/backup/cancel-state.ts
@@ -0,0 +1,64 @@
+interface JobCancellationState {
+  requested: Set<string>
+  controllers: Map<string, AbortController>
+}
+
+const CANCELLED_CODE = 'JOB_CANCELLED'
+
+const state = (globalThis as typeof globalThis & {
+  __pichostJobCancellationState?: JobCancellationState
+}).__pichostJobCancellationState ?? {
+  requested: new Set<string>(),
+  controllers: new Map<string, AbortController>()
+}
+;(globalThis as typeof globalThis & {
+  __pichostJobCancellationState?: JobCancellationState
+}).__pichostJobCancellationState = state
+
+export function createJobCancelledError(): Error {
+  const error = new Error('任务已取消')
+  error.name = CANCELLED_CODE
+  return error
+}
+
+export function isJobCancelledError(error: unknown): boolean {
+  return error instanceof Error && error.name === CANCELLED_CODE
+}
+
+export function beginJobCancellationScope(jobId: string): void {
+  state.requested.delete(jobId)
+  state.controllers.get(jobId)?.abort()
+  state.controllers.set(jobId, new AbortController())
+}
+
+export function endJobCancellationScope(jobId: string): void {
+  state.controllers.delete(jobId)
+  state.requested.delete(jobId)
+}
+
+export function requestJobCancellation(jobId: string): void {
+  state.requested.add(jobId)
+  state.controllers.get(jobId)?.abort(createJobCancelledError())
+}
+
+export function isJobCancellationRequested(jobId: string): boolean {
+  return state.requested.has(jobId)
+}
+
+export function getJobAbortSignal(jobId: string): AbortSignal {
+  return state.controllers.get(jobId)?.signal ?? new AbortController().signal
+}
+
+export function getJobOperationSignal(
+  jobId: string,
+  timeoutMs: number
+): AbortSignal {
+  return AbortSignal.any([
+    getJobAbortSignal(jobId),
+    AbortSignal.timeout(timeoutMs)
+  ])
+}
+
+export function throwIfJobCancellationRequested(jobId: string): void {
+  if (isJobCancellationRequested(jobId)) throw createJobCancelledError()
+}
diff --git a/server/utils/backup/runner.ts b/server/utils/backup/runner.ts
index 82573ae..f49d03c 100644
--- a/server/utils/backup/runner.ts
+++ b/server/utils/backup/runner.ts
@@ -10,6 +10,11 @@ import {
   recoverInterruptedBackupJobs,
   type BackupJob
 } from './jobs'
+import {
+  beginJobCancellationScope,
+  endJobCancellationScope,
+  requestJobCancellation
+} from './cancel-state'
 
 interface BackupRunnerState {
   running: boolean
@@ -42,11 +47,8 @@ export function cancelBackupJob(jobId: string): boolean {
   if (!job || (job.status !== 'running' && job.status !== 'pending')) {
     return false
   }
-  markJobFailed(jobId, '任务已取消')
-  if (runnerState.currentJobId === jobId) {
-    runnerState.running = false
-    runnerState.currentJobId = null
-  }
+  requestJobCancellation(jobId)
+  markJobFailed(jobId, '任务已取消', '已请求取消，正在停止…')
   return true
 }
 
@@ -59,14 +61,18 @@ export function scheduleBackupJob(
   }
   runnerState.running = true
   runnerState.currentJobId = job.id
+  beginJobCancellationScope(job.id)
   markJobRunning(job.id)
 
   setImmediate(() => {
     runner()
       .catch(() => {})
       .finally(() => {
-        runnerState.running = false
-        runnerState.currentJobId = null
+        endJobCancellationScope(job.id)
+        if (runnerState.currentJobId === job.id) {
+          runnerState.running = false
+          runnerState.currentJobId = null
+        }
       })
   })
 }
diff --git a/server/utils/site-sync/abandon.ts b/server/utils/site-sync/abandon.ts
new file mode 100644
index 0000000..9a9ab38
--- /dev/null
+++ b/server/utils/site-sync/abandon.ts
@@ -0,0 +1,66 @@
+import {
+  getBackupJob,
+  updateBackupJob,
+  type BackupJob
+} from '../backup/jobs'
+import { cleanupSiteSyncJobArtifacts } from './artifacts'
+import { fetchSiteSyncJson } from './runner'
+
+interface CleanupResult {
+  deleted: number
+  referenced: number
+  failed: number
+}
+
+export async function abandonSiteSyncJob(
+  jobId: string,
+  token: string,
+  userId: number
+): Promise<BackupJob> {
+  const job = getBackupJob(jobId, userId)
+  if (!job || job.type !== 'site_sync') throw new Error('同步任务不存在')
+  if (job.status !== 'failed') throw new Error('只能放弃已停止的同步任务')
+
+  const direction = job.payload.direction === 'pull' ? 'pull' : 'push'
+  const targetBaseUrl = typeof job.payload.targetBaseUrl === 'string'
+    ? job.payload.targetBaseUrl.replace(/\/+$/, '')
+    : ''
+  let cleanup: CleanupResult
+  if (direction === 'push') {
+    if (!targetBaseUrl || !token) {
+      throw new Error('放弃推送任务并清理目标站残留时，需要目标站 Token')
+    }
+    cleanup = await fetchSiteSyncJson<CleanupResult>(
+      `${targetBaseUrl}/api/site-sync/cleanup`,
+      token,
+      {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({ jobId })
+      }
+    )
+  } else {
+    cleanup = await cleanupSiteSyncJobArtifacts(jobId)
+  }
+
+  if (cleanup.failed > 0) {
+    throw new Error(`同步残留清理失败：${cleanup.failed} 个对象`)
+  }
+
+  const message = `已放弃同步 · 清理 ${cleanup.deleted} 个残留对象`
+  updateBackupJob(jobId, {
+    status: 'failed',
+    message,
+    error: '已放弃同步',
+    finishedAt: new Date().toISOString(),
+    payload: {
+      ...job.payload,
+      resumable: false,
+      abandoned: true,
+      cancelled: false,
+      failedKeys: [],
+      cleanup
+    }
+  })
+  return getBackupJob(jobId, userId)!
+}
diff --git a/server/utils/site-sync/artifacts.ts b/server/utils/site-sync/artifacts.ts
new file mode 100644
index 0000000..683aad4
--- /dev/null
+++ b/server/utils/site-sync/artifacts.ts
@@ -0,0 +1,172 @@
+import { getDb } from '../db'
+import { getImageIndexRow } from '../image-index'
+import { getBackendById } from '../storage/resolver'
+import { hlsSegmentNames } from '../transcode'
+
+interface ArtifactRow {
+  job_id: string
+  media_key: string
+  key: string
+  backend_id: string
+  created: number
+  updated_at: string
+}
+
+function ensureArtifactSchema(): void {
+  getDb().exec(`
+    CREATE TABLE IF NOT EXISTS site_sync_artifacts (
+      job_id TEXT NOT NULL,
+      media_key TEXT NOT NULL,
+      key TEXT NOT NULL,
+      backend_id TEXT NOT NULL,
+      created INTEGER NOT NULL DEFAULT 0,
+      updated_at TEXT NOT NULL,
+      PRIMARY KEY(job_id, key)
+    );
+    CREATE INDEX IF NOT EXISTS idx_site_sync_artifacts_updated
+      ON site_sync_artifacts(updated_at);
+    CREATE INDEX IF NOT EXISTS idx_site_sync_artifacts_media
+      ON site_sync_artifacts(job_id, media_key);
+  `)
+}
+
+export function recordSiteSyncArtifact(input: {
+  jobId: string
+  mediaKey: string
+  key: string
+  backendId: string
+  created: boolean
+}): void {
+  ensureArtifactSchema()
+  getDb().prepare(`
+    INSERT INTO site_sync_artifacts
+      (job_id, media_key, key, backend_id, created, updated_at)
+    VALUES (?, ?, ?, ?, ?, ?)
+    ON CONFLICT(job_id, key) DO UPDATE SET
+      media_key = excluded.media_key,
+      backend_id = excluded.backend_id,
+      created = MAX(site_sync_artifacts.created, excluded.created),
+      updated_at = excluded.updated_at
+  `).run(
+    input.jobId,
+    input.mediaKey,
+    input.key,
+    input.backendId,
+    input.created ? 1 : 0,
+    new Date().toISOString()
+  )
+}
+
+export function completeSiteSyncMediaArtifacts(
+  jobId: string,
+  mediaKey: string
+): void {
+  ensureArtifactSchema()
+  getDb().prepare(`
+    DELETE FROM site_sync_artifacts
+    WHERE job_id = ? AND media_key = ?
+  `).run(jobId, mediaKey)
+}
+
+async function streamToString(stream: NodeJS.ReadableStream): Promise<string> {
+  const chunks: Buffer[] = []
+  for await (const chunk of stream) {
+    chunks.push(Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk))
+  }
+  return Buffer.concat(chunks).toString('utf8')
+}
+
+async function isReferencedByCommittedMedia(
+  mediaKey: string,
+  key: string
+): Promise<boolean> {
+  const row = getImageIndexRow(mediaKey)
+  if (!row) return false
+  if (key === row.key || key === row.thumb_key || key === row.hls_key) {
+    return true
+  }
+  if (!row.hls_key) return false
+
+  const slash = row.hls_key.lastIndexOf('/')
+  if (slash < 0 || !key.startsWith(`${row.hls_key.slice(0, slash)}/`)) {
+    return false
+  }
+
+  try {
+    const backend = await getBackendById(row.backend_id)
+    if (!backend) return true
+    const playlist = await streamToString(await backend.createStream(row.hls_key))
+    const dir = row.hls_key.slice(0, slash)
+    return hlsSegmentNames(playlist).some(name => key === `${dir}/${name}`)
+  } catch {
+    // If the playlist cannot be read, keep the object rather than risk data loss.
+    return true
+  }
+}
+
+export async function cleanupSiteSyncJobArtifacts(jobId: string): Promise<{
+  deleted: number
+  referenced: number
+  failed: number
+}> {
+  ensureArtifactSchema()
+  const rows = getDb().prepare(`
+    SELECT job_id, media_key, key, backend_id, created, updated_at
+    FROM site_sync_artifacts
+    WHERE job_id = ?
+    ORDER BY updated_at ASC
+  `).all(jobId) as unknown as ArtifactRow[]
+
+  let deleted = 0
+  let referenced = 0
+  let failed = 0
+  for (const row of rows) {
+    if (Number(row.created) !== 1) {
+      getDb().prepare(`
+        DELETE FROM site_sync_artifacts WHERE job_id = ? AND key = ?
+      `).run(jobId, row.key)
+      continue
+    }
+
+    try {
+      if (await isReferencedByCommittedMedia(row.media_key, row.key)) {
+        referenced++
+      } else {
+        const backend = await getBackendById(row.backend_id)
+        if (!backend) throw new Error('存储后端不存在')
+        if (await backend.head(row.key)) {
+          await backend.delete(row.key)
+          deleted++
+        }
+      }
+      getDb().prepare(`
+        DELETE FROM site_sync_artifacts WHERE job_id = ? AND key = ?
+      `).run(jobId, row.key)
+    } catch {
+      failed++
+    }
+  }
+
+  return { deleted, referenced, failed }
+}
+
+export async function cleanupExpiredSiteSyncArtifacts(
+  maxAgeMs = 24 * 60 * 60 * 1000
+): Promise<{ jobs: number, deleted: number, failed: number }> {
+  ensureArtifactSchema()
+  const cutoff = new Date(Date.now() - maxAgeMs).toISOString()
+  const rows = getDb().prepare(`
+    SELECT DISTINCT job_id
+    FROM site_sync_artifacts
+    WHERE updated_at < ?
+  `).all(cutoff) as Array<{ job_id: string }>
+
+  let deleted = 0
+  let failed = 0
+  for (const row of rows) {
+    const result = await cleanupSiteSyncJobArtifacts(row.job_id)
+    deleted += result.deleted
+    failed += result.failed
+  }
+  return { jobs: rows.length, deleted, failed }
+}
diff --git a/server/utils/site-sync/runner.test.ts b/server/utils/site-sync/runner.test.ts
index c7d59af..a7a2f21 100644
--- a/server/utils/site-sync/runner.test.ts
+++ b/server/utils/site-sync/runner.test.ts
@@ -1,5 +1,11 @@
 import { afterEach, describe, expect, it, vi } from 'vitest'
 import { fetchSiteSyncJson, retrySiteSyncOperation } from './runner'
+import {
+  beginJobCancellationScope,
+  endJobCancellationScope,
+  getJobAbortSignal,
+  requestJobCancellation
+} from '../backup/cancel-state'
 
 afterEach(() => {
   vi.unstubAllGlobals()
@@ -52,4 +58,17 @@ describe('fetchSiteSyncJson', () => {
     await expect(retrySiteSyncOperation(operation)).rejects.toThrow('database is busy')
     expect(operation).toHaveBeenCalledTimes(3)
   })
+
+  it('stops retrying immediately when the job is cancelled', async () => {
+    const jobId = 'cancel-test'
+    beginJobCancellationScope(jobId)
+    const operation = vi.fn().mockRejectedValue(new Error('connection reset'))
+    const result = retrySiteSyncOperation(operation, getJobAbortSignal(jobId))
+
+    setTimeout(() => requestJobCancellation(jobId), 25)
+
+    await expect(result).rejects.toThrow('任务已取消')
+    expect(operation).toHaveBeenCalledTimes(1)
+    endJobCancellationScope(jobId)
+  })
 })
diff --git a/server/utils/site-sync/runner.ts b/server/utils/site-sync/runner.ts
index 407494f..4c90c41 100644
--- a/server/utils/site-sync/runner.ts
+++ b/server/utils/site-sync/runner.ts
@@ -1,4 +1,5 @@
 import { basename } from 'node:path'
+import type { Readable } from 'node:stream'
 import { contentTypeFromKey } from '../content-type'
 import {
   getImageIndexRow,
@@ -22,7 +23,19 @@ import {
   markJobFailed,
   updateBackupJob
 } from '../backup/jobs'
+import {
+  createJobCancelledError,
+  getJobAbortSignal,
+  getJobOperationSignal,
+  isJobCancellationRequested,
+  isJobCancelledError,
+  throwIfJobCancellationRequested
+} from '../backup/cancel-state'
 import { applySiteSyncMedia } from './apply'
+import {
+  completeSiteSyncMediaArtifacts,
+  recordSiteSyncArtifact
+} from './artifacts'
 import { toSiteSyncMediaTransferWithTags } from './manifest'
 import type {
   SiteSyncDirection,
@@ -49,9 +62,19 @@ export function registerSiteSyncToken(jobId: string, token: string): void {
   tokens.set(jobId, token)
 }
 
-async function streamToBuffer(stream: NodeJS.ReadableStream): Promise<Buffer> {
+const SITE_SYNC_JSON_TIMEOUT_MS = 2 * 60 * 1000
+const SITE_SYNC_OBJECT_TIMEOUT_MS = 15 * 60 * 1000
+
+async function streamToBuffer(
+  stream: Readable,
+  signal?: AbortSignal
+): Promise<Buffer> {
   const chunks: Buffer[] = []
   for await (const chunk of stream) {
+    if (signal?.aborted) {
+      stream.destroy(createJobCancelledError())
+      throw createJobCancelledError()
+    }
     chunks.push(Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk))
   }
   return Buffer.concat(chunks)
@@ -71,21 +94,46 @@ async function responseError(response: Response): Promise<Error> {
 
 const SITE_SYNC_MAX_ATTEMPTS = 3
 
+function normalizeSiteSyncError(error: Error): Error {
+  if (error.name === 'TimeoutError') {
+    return new Error('目标站点连接超时或无响应')
+  }
+  if (error instanceof TypeError && /fetch failed|terminated/i.test(error.message)) {
+    return new Error('目标站点无法连接')
+  }
+  return error
+}
+
 export async function retrySiteSyncOperation<T>(
-  operation: () => Promise<T>
+  operation: () => Promise<T>,
+  signal?: AbortSignal
 ): Promise<T> {
+  if (signal?.aborted) throw createJobCancelledError()
   let lastError: Error | null = null
   for (let attempt = 1; attempt <= SITE_SYNC_MAX_ATTEMPTS; attempt++) {
     try {
       return await operation()
     } catch (error) {
+      if (signal?.aborted) throw createJobCancelledError()
       lastError = error instanceof Error ? error : new Error('两站点同步失败')
       if (attempt < SITE_SYNC_MAX_ATTEMPTS) {
-        await new Promise(resolve => setTimeout(resolve, attempt * 500))
+        await new Promise<void>((resolve, reject) => {
+          const onAbort = () => {
+            clearTimeout(timer)
+            reject(createJobCancelledError())
+          }
+          const timer = setTimeout(() => {
+            signal?.removeEventListener('abort', onAbort)
+            resolve()
+          }, attempt * 500)
+          signal?.addEventListener('abort', onAbort, { once: true })
+        })
       }
     }
   }
-  throw lastError ?? new Error('两站点同步失败')
+  throw lastError
+    ? normalizeSiteSyncError(lastError)
+    : new Error('两站点同步失败')
 }
 
 async function fetchSiteSyncJsonOnce<T>(
@@ -107,14 +155,25 @@ async function fetchSiteSyncJsonOnce<T>(
 export async function fetchSiteSyncJson<T>(
   url: string,
   token: string,
-  init?: RequestInit
+  init?: RequestInit,
+  signal?: AbortSignal
 ): Promise<T> {
-  return retrySiteSyncOperation(() => (
-    fetchSiteSyncJsonOnce<T>(url, token, init)
-  ))
+  return retrySiteSyncOperation(
+    () => fetchSiteSyncJsonOnce<T>(url, token, {
+      ...init,
+      signal: signal
+        ? AbortSignal.any([
+            signal,
+            AbortSignal.timeout(SITE_SYNC_JSON_TIMEOUT_MS)
+          ])
+        : AbortSignal.timeout(SITE_SYNC_JSON_TIMEOUT_MS)
+    }),
+    signal
+  )
 }
 
 async function uploadObject(
+  jobId: string,
   options: SiteSyncOptions,
   token: string,
   backend: StorageBackend,
@@ -124,9 +183,15 @@ async function uploadObject(
 ): Promise<void> {
   const stored = await backend.head(key)
   if (!stored) throw new Error(`源文件不存在：${key}`)
-  const bytes = await streamToBuffer(await backend.createStream(key))
+  const bytes = await streamToBuffer(
+    await backend.createStream(key),
+    getJobAbortSignal(jobId)
+  )
+  throwIfJobCancellationRequested(jobId)
   const form = new FormData()
   const isPrimary = key === row.key
+  form.append('jobId', jobId)
+  form.append('mediaKey', row.key)
   form.append('key', key)
   form.append('conflictMode', options.conflictMode)
   form.append('ownerUsername', ownerUsername ?? '')
@@ -143,11 +208,16 @@ async function uploadObject(
   await fetchSiteSyncJsonOnce<{ success: boolean }>(
     targetUrl(options.targetBaseUrl, '/api/site-sync/object'),
     token,
-    { method: 'POST', body: form }
+    {
+      method: 'POST',
+      body: form,
+      signal: getJobOperationSignal(jobId, SITE_SYNC_OBJECT_TIMEOUT_MS)
+    }
   )
 }
 
 async function downloadSiteSyncObject(
+  jobId: string,
   options: SiteSyncOptions,
   token: string,
   key: string
@@ -160,7 +230,8 @@ async function downloadSiteSyncObject(
     {
       headers: {
         'Auth-Token': token
-      }
+      },
+      signal: getJobOperationSignal(jobId, SITE_SYNC_OBJECT_TIMEOUT_MS)
     }
   )
   if (!response.ok) throw await responseError(response)
@@ -173,6 +244,7 @@ async function runSiteSyncPull(
   token: string
 ): Promise<void> {
   const job = getBackupJob(jobId)
+  const jobSignal = getJobAbortSignal(jobId)
   const checkpoint = job?.payload ?? {}
   let lastMediaKey = typeof checkpoint.lastMediaKey === 'string'
     ? checkpoint.lastMediaKey
@@ -189,7 +261,7 @@ async function runSiteSyncPull(
       : []
   )
 
-  const saveCheckpoint = (message: string) => {
+  const saveCheckpoint = (message: string, cancelled = false) => {
     updateBackupJob(jobId, {
       progress: scanned,
       total: totalMedia,
@@ -198,6 +270,7 @@ async function runSiteSyncPull(
         targetBaseUrl: options.targetBaseUrl,
         conflictMode: options.conflictMode,
         direction: 'pull',
+        cancelled,
         lastMediaKey,
         scanned,
         added,
@@ -215,11 +288,19 @@ async function runSiteSyncPull(
     `扫描 ${scanned}/${totalMedia || scanned} · 新增 ${added} · 跳过 ${skipped} · 失败 ${failedKeys.size}${suffix}`
   )
   const failAndCheckpoint = (error: unknown) => {
-    const message = progressMessage(' · 已保存断点')
-    saveCheckpoint(message)
+    const cancelled = isJobCancellationRequested(jobId)
+      || isJobCancelledError(error)
+    const message = cancelled
+      ? progressMessage(' · 已取消，已保存断点')
+      : progressMessage(' · 已保存断点')
+    saveCheckpoint(message, cancelled)
     markJobFailed(
       jobId,
-      error instanceof Error ? error.message : '从目标站点拉取失败',
+      cancelled
+        ? '任务已取消'
+        : error instanceof Error
+          ? error.message
+          : '从目标站点拉取失败',
       message
     )
   }
@@ -228,21 +309,22 @@ async function runSiteSyncPull(
     const targetUsers = new Set(
       (await fetchSiteSyncJson<SiteSyncUsers>(
         targetUrl(options.targetBaseUrl, '/api/site-sync/users'),
-        token
+        token,
+        undefined,
+        jobSignal
       )).users
     )
-    const localUserMap = listUserIdUsernameMap()
-    const localUsers = new Set(localUserMap.values())
-    const missingUsers = [...targetUsers].filter(name => !localUsers.has(name))
-    if (missingUsers.length) {
-      throw new Error(`当前站点缺少同名用户：${missingUsers.join('、')}`)
-    }
 
-    const backend = await retrySiteSyncOperation(() => getActiveBackend())
+    const backend = await retrySiteSyncOperation(
+      () => getActiveBackend(),
+      jobSignal
+    )
     const actorUserId = job?.userId ?? getPrimaryAdminUserId() ?? 0
     const readMediaPage = (path: string) => fetchSiteSyncJson<SiteSyncMediaPage>(
       targetUrl(options.targetBaseUrl, path),
-      token
+      token,
+      undefined,
+      jobSignal
     )
 
     const processBundleOnce = async (
@@ -250,11 +332,16 @@ async function runSiteSyncPull(
       isRetry: boolean
     ): Promise<'added' | 'skipped'> => {
       const { media, assets } = bundle
+      throwIfJobCancellationRequested(jobId)
+      if (media.ownerUsername && !targetUsers.has(media.ownerUsername)) {
+        throw new Error(`当前站点缺少同名用户：${media.ownerUsername}`)
+      }
       if (
         !isRetry
         && options.conflictMode === 'skip'
         && getImageIndexRow(media.key)
       ) {
+        completeSiteSyncMediaArtifacts(jobId, media.key)
         return 'skipped'
       }
 
@@ -262,23 +349,31 @@ async function runSiteSyncPull(
         ? findUserByUsername(media.ownerUsername)
         : null
       for (const asset of assets) {
-        if (
-          options.conflictMode === 'skip'
-          && await backend.head(asset.key)
-        ) {
+        throwIfJobCancellationRequested(jobId)
+        const existedBefore = Boolean(await backend.head(asset.key))
+        if (options.conflictMode === 'skip' && existedBefore) {
           continue
         }
         const bytes = await downloadSiteSyncObject(
+          jobId,
           options,
           token,
           asset.key
         )
+        throwIfJobCancellationRequested(jobId)
         if (bytes.length !== asset.size) {
           throw new Error(
             `同步对象大小不一致：${asset.key}，预期 ${asset.size}，实际 ${bytes.length}`
           )
         }
         const isPrimary = asset.key === media.key
+        recordSiteSyncArtifact({
+          jobId,
+          mediaKey: media.key,
+          key: asset.key,
+          backendId: backend.id,
+          created: !existedBefore
+        })
         await backend.put(asset.key, new Uint8Array(bytes), {
           originalName: isPrimary ? media.originalName : basename(asset.key),
           uploadedAt: media.uploadedAt,
@@ -295,13 +390,18 @@ async function runSiteSyncPull(
                 ? 'file'
                 : 'image'
         })
+        throwIfJobCancellationRequested(jobId)
       }
 
       await applySiteSyncMedia(media, 'overwrite', actorUserId)
+      completeSiteSyncMediaArtifacts(jobId, media.key)
       return 'added'
     }
     const processBundle = (bundle: SiteSyncMediaBundle, isRetry: boolean) => (
-      retrySiteSyncOperation(() => processBundleOnce(bundle, isRetry))
+      retrySiteSyncOperation(
+        () => processBundleOnce(bundle, isRetry),
+        jobSignal
+      )
     )
     const recordOutcome = (outcome: 'added' | 'skipped', fileCount: number) => {
       if (outcome === 'added') added += 1
@@ -382,6 +482,7 @@ async function runSiteSyncPull(
       return
     }
 
+    throwIfJobCancellationRequested(jobId)
     totalFiles = filesSynced
     markJobDone(jobId, {
       message: `扫描 ${scanned}/${totalMedia || scanned} · 新增 ${added} · 跳过 ${skipped} · 失败 0`,
@@ -412,6 +513,7 @@ export async function runSiteSyncJob(
 ): Promise<void> {
   const token = tokens.get(jobId)
   if (!token) throw new Error('同步 Token 不可用，请重新发起任务')
+  const jobSignal = getJobAbortSignal(jobId)
 
   try {
     if (options.direction === 'pull') {
@@ -421,7 +523,9 @@ export async function runSiteSyncJob(
 
     const inventory = await fetchSiteSyncJson<SiteSyncInventory>(
       targetUrl(options.targetBaseUrl, '/api/site-sync/inventory'),
-      token
+      token,
+      undefined,
+      jobSignal
     )
     const targetUsers = new Set(inventory.users)
     const targetMedia = new Set(inventory.mediaKeys)
@@ -466,6 +570,7 @@ export async function runSiteSyncJob(
     })
 
     for (const row of rows) {
+      throwIfJobCancellationRequested(jobId)
       const backend = await getBackendForKey(row.key)
       let assetKeys: string[]
       try {
@@ -487,7 +592,7 @@ export async function runSiteSyncJob(
       })
     }
 
-    const saveCheckpoint = (message: string) => {
+    const saveCheckpoint = (message: string, cancelled = false) => {
       updateBackupJob(jobId, {
         progress: scanned,
         total: rows.length,
@@ -496,6 +601,7 @@ export async function runSiteSyncJob(
           targetBaseUrl: options.targetBaseUrl,
           conflictMode: options.conflictMode,
           direction: 'push',
+          cancelled,
           lastMediaKey,
           scanned,
           added,
@@ -520,11 +626,22 @@ export async function runSiteSyncJob(
     let lastCheckpointAt = 0
     const processPlanOnce = async (plan: typeof plans[number], isRetry: boolean) => {
       const { row, ownerUsername, backend, keys } = plan
+      throwIfJobCancellationRequested(jobId)
       if (
         !isRetry
         && options.conflictMode === 'skip'
         && targetMedia.has(row.key)
       ) {
+        await fetchSiteSyncJsonOnce<{ success: boolean }>(
+          targetUrl(options.targetBaseUrl, '/api/site-sync/complete'),
+          token,
+          {
+            method: 'POST',
+            headers: { 'Content-Type': 'application/json' },
+            body: JSON.stringify({ jobId, mediaKey: row.key }),
+            signal: getJobOperationSignal(jobId, SITE_SYNC_JSON_TIMEOUT_MS)
+          }
+        )
         skipped += 1
         filesSynced = Math.min(totalFiles, filesSynced + keys.length)
         failedKeys.delete(row.key)
@@ -532,6 +649,7 @@ export async function runSiteSyncJob(
       }
 
       for (const key of keys) {
+        throwIfJobCancellationRequested(jobId)
         const stored = await backend.head(key)
         if (!stored) throw new Error(`源文件不存在：${key}`)
         if (
@@ -540,9 +658,18 @@ export async function runSiteSyncJob(
         ) {
           continue
         }
-        await uploadObject(options, token, backend, row, ownerUsername, key)
+        await uploadObject(
+          jobId,
+          options,
+          token,
+          backend,
+          row,
+          ownerUsername,
+          key
+        )
       }
 
+      throwIfJobCancellationRequested(jobId)
       await fetchSiteSyncJsonOnce<{ success: boolean }>(
         targetUrl(options.targetBaseUrl, '/api/site-sync/media'),
         token,
@@ -550,9 +677,11 @@ export async function runSiteSyncJob(
           method: 'POST',
           headers: { 'Content-Type': 'application/json' },
           body: JSON.stringify({
+            jobId,
             media: toSiteSyncMediaTransferWithTags(row, ownerUsername),
             conflictMode: options.conflictMode
-          })
+          }),
+          signal: getJobOperationSignal(jobId, SITE_SYNC_JSON_TIMEOUT_MS)
         }
       )
 
@@ -563,18 +692,29 @@ export async function runSiteSyncJob(
     const processPlan = (
       plan: typeof plans[number],
       isRetry: boolean
-    ) => retrySiteSyncOperation(() => processPlanOnce(plan, isRetry))
+    ) => retrySiteSyncOperation(
+      () => processPlanOnce(plan, isRetry),
+      jobSignal
+    )
 
     const retryPlans = plans.filter(plan => failedKeys.has(plan.row.key))
     for (const plan of retryPlans) {
       try {
         await processPlan(plan, true)
         lastMediaKey = plan.row.key
-      } catch {
+      } catch (error) {
         failedKeys.add(plan.row.key)
-        const message = `扫描 ${scanned}/${rows.length} · 新增 ${added} · 跳过 ${skipped} · 失败 ${failedKeys.size} · 已保存断点`
-        saveCheckpoint(message)
-        markJobFailed(jobId, '连续 3 次重试失败，已保存断点', message)
+        const cancelled = isJobCancellationRequested(jobId)
+          || isJobCancelledError(error)
+        const message = `扫描 ${scanned}/${rows.length} · 新增 ${added} · 跳过 ${skipped} · 失败 ${failedKeys.size} · ${cancelled ? '已取消，' : ''}已保存断点`
+        saveCheckpoint(message, cancelled)
+        markJobFailed(
+          jobId,
+          cancelled
+            ? '任务已取消'
+            : '连续 3 次重试失败，已保存断点',
+          message
+        )
         return
       }
     }
@@ -584,12 +724,20 @@ export async function runSiteSyncJob(
       scanned += 1
       try {
         await processPlan(plan, false)
-      } catch {
+      } catch (error) {
         failedKeys.add(plan.row.key)
         lastMediaKey = plan.row.key
-        const message = `扫描 ${scanned}/${rows.length} · 新增 ${added} · 跳过 ${skipped} · 失败 ${failedKeys.size} · 已保存断点`
-        saveCheckpoint(message)
-        markJobFailed(jobId, '连续 3 次重试失败，已保存断点', message)
+        const cancelled = isJobCancellationRequested(jobId)
+          || isJobCancelledError(error)
+        const message = `扫描 ${scanned}/${rows.length} · 新增 ${added} · 跳过 ${skipped} · 失败 ${failedKeys.size} · ${cancelled ? '已取消，' : ''}已保存断点`
+        saveCheckpoint(message, cancelled)
+        markJobFailed(
+          jobId,
+          cancelled
+            ? '任务已取消'
+            : '连续 3 次重试失败，已保存断点',
+          message
+        )
         return
       }
       lastMediaKey = plan.row.key
@@ -614,6 +762,7 @@ export async function runSiteSyncJob(
       return
     }
 
+    throwIfJobCancellationRequested(jobId)
     markJobDone(jobId, {
       message: `扫描 ${rows.length}/${rows.length} · 新增 ${added} · 跳过 ${skipped} · 失败 0`,
       payload: {
@@ -632,6 +781,10 @@ export async function runSiteSyncJob(
       }
     })
   } catch (error) {
+    if (isJobCancellationRequested(jobId) || isJobCancelledError(error)) {
+      markJobFailed(jobId, '任务已取消', '任务已取消')
+      return
+    }
     const message = error instanceof Error ? error.message : '两站点同步失败'
     markJobFailed(jobId, message)
     throw error
diff --git a/server/utils/storage/index.ts b/server/utils/storage/index.ts
index 5b13899..7ec7360 100644
--- a/server/utils/storage/index.ts
+++ b/server/utils/storage/index.ts
@@ -1,4 +1,4 @@
-export { getActiveBackend, getBackendForKey, getActiveBackendRow, getBackendRowForKey } from './resolver'
+export { getActiveBackend, getBackendById, getBackendForKey, getActiveBackendRow, getBackendRowForKey } from './resolver'
 export { LocalStorageBackend } from './local'
 export { S3StorageBackend, buildObjectKey, parseS3Config, validateS3Config } from './s3'
 export {
diff --git a/server/utils/storage/local.ts b/server/utils/storage/local.ts
index e92fbe8..d3dec66 100644
--- a/server/utils/storage/local.ts
+++ b/server/utils/storage/local.ts
@@ -1,3 +1,4 @@
+import { randomUUID } from 'node:crypto'
 import { createReadStream, promises as fs } from 'node:fs'
 import type { ReadStream } from 'node:fs'
 import { dirname, join } from 'node:path'
@@ -7,6 +8,7 @@ import { validateStorageKey } from '../image-key'
 import type { StoredImage, StoredImageMeta, StorageBackend } from './types'
 
 const META_SUFFIX = '.meta.json'
+const ATOMIC_TEMP_DIR = '.pichost-tmp'
 
 function keyToFilePath(key: string): string {
   return join(getDataDir(), ...key.split('/'))
@@ -39,8 +41,36 @@ export class LocalStorageBackend implements StorageBackend {
 
   async put(key: string, bytes: Uint8Array, _meta: StoredImageMeta): Promise<void> {
     const filePath = keyToFilePath(key)
+    const tempDir = join(getDataDir(), ATOMIC_TEMP_DIR)
+    const tempPath = join(tempDir, `${randomUUID()}.part`)
+    await fs.mkdir(tempDir, { recursive: true })
     await fs.mkdir(dirname(filePath), { recursive: true })
-    await fs.writeFile(filePath, bytes)
+
+    const handle = await fs.open(tempPath, 'w')
+    try {
+      await handle.writeFile(bytes)
+      await handle.sync()
+    } finally {
+      await handle.close()
+    }
+
+    try {
+      await fs.rename(tempPath, filePath)
+    } catch (error) {
+      await fs.rm(tempPath, { force: true }).catch(() => {})
+      throw error
+    }
+
+    try {
+      const directory = await fs.open(dirname(filePath), 'r')
+      try {
+        await directory.sync()
+      } finally {
+        await directory.close()
+      }
+    } catch {
+      // The rename already completed; directory fsync is best-effort on macOS.
+    }
   }
 
   async head(key: string): Promise<StoredImage | null> {
@@ -93,3 +123,31 @@ export class LocalStorageBackend implements StorageBackend {
     return { count: 0, bytes: 0 }
   }
 }
+
+export async function cleanupLocalAtomicTempFiles(
+  maxAgeMs = 60 * 60 * 1000
+): Promise<number> {
+  const tempDir = join(getDataDir(), ATOMIC_TEMP_DIR)
+  let entries
+  try {
+    entries = await fs.readdir(tempDir, { withFileTypes: true })
+  } catch {
+    return 0
+  }
+
+  const cutoff = Date.now() - maxAgeMs
+  let removed = 0
+  for (const entry of entries) {
+    if (!entry.isFile() || !entry.name.endsWith('.part')) continue
+    const path = join(tempDir, entry.name)
+    try {
+      const stat = await fs.stat(path)
+      if (stat.mtimeMs > cutoff) continue
+      await fs.rm(path, { force: true })
+      removed++
+    } catch {
+      // A later startup will retry stale temporary files.
+    }
+  }
+  return removed
+}
diff --git a/server/utils/storage/resolver.ts b/server/utils/storage/resolver.ts
index 6859977..20cf622 100644
--- a/server/utils/storage/resolver.ts
+++ b/server/utils/storage/resolver.ts
@@ -53,6 +53,18 @@ export async function getBackendForKey(key: string): Promise<StorageBackend> {
   }
 }
 
+export async function getBackendById(
+  backendId: string
+): Promise<StorageBackend | null> {
+  const fromEnv = createBackendFromEnv()
+  if (fromEnv) return fromEnv.id === backendId ? fromEnv : null
+
+  ensureDefaultBackends()
+  const row = getStorageBackendRow(backendId)
+  if (!row) return null
+  return createBackendInstance(row)
+}
+
 export function getActiveBackendRow(): StorageBackendRow | null {
   const fromEnv = createBackendFromEnv()
   if (fromEnv) {