diff --git a/lib/store.js b/lib/store.js
index 0467927..bf20a7a 100644
--- a/lib/store.js
+++ b/lib/store.js
@@ -222,10 +222,10 @@ export function createStore(options = {}) {
         error.code = 'STORE_CORRUPT'
         try {
           const bak = `${filePath}.corrupt.${Date.now()}.bak`
-          await writeFile(bak, raw, 'utf8')
+          await rename(filePath, bak)
           error.message = `${error.message} (backup: ${bak})`
         } catch {
-          // best-effort backup
+          // best-effort quarantine; persist() below overwrites either way
         }
         console.warn(`[dsh-ops-cron] ${error.message}`)
         state = emptyState()
diff --git a/lib/tools.js b/lib/tools.js
index 9ca9d19..a229f9d 100644
--- a/lib/tools.js
+++ b/lib/tools.js
@@ -41,9 +41,10 @@ const JOB_SCHEMA = {
     schedule: { type: 'object', additionalProperties: true },
     createdAt: { type: 'number' },
     updatedAt: { type: 'number' },
-    lastRunAt: { type: ['number', 'null'] },
-    lastStatus: { type: ['string', 'null'] },
-    nextRunAt: { type: ['number', 'null'] },
+    // Host assertSupportedJsonSchema rejects type arrays — use oneOf for nullables.
+    lastRunAt: { oneOf: [{ type: 'number' }, { type: 'null' }] },
+    lastStatus: { oneOf: [{ type: 'string' }, { type: 'null' }] },
+    nextRunAt: { oneOf: [{ type: 'number' }, { type: 'null' }] },
   },
 }
 
@@ -497,8 +498,9 @@ export function cronGuidanceText(nowMs = Date.now(), timeZone = 'Asia/Shanghai')
     'Agent preset: omit agent_preset to inherit (WhatsApp chat/group preset → creating session → Host default). Pass agent_preset to pin a preset for every scheduled run.',
     'When the user asks to look at, create, pause, resume, or delete 定时任务 / scheduled tasks / cron jobs:',
     '1. If cron_list / cron_create / cron_pause / cron_resume / cron_delete are in your tool list, call them.',
-    '2. If they are not listed, search/unlock tools or skills with query "定时任务" or "cron" (skill_search, skill_load, or dev_tool_search) and then call them.',
-    '3. Never run crontab, never read /etc/cron*, and never say there are no tasks until cron_list has returned.',
+    '2. If they are not listed, load skill "scheduled-tasks" via the skill tool (exact name), then retry the cron_* tools. Those tools are registered by the dsh-ops-cron plugin — they are not unlocked by skill_search/dev_tool_search (those names are obsolete).',
+    '3. If cron_* still return unknown tool after loading the skill, the plugin failed to register (check Host logs for unsupported JSON schema). Tell the user; do not invent crontab workarounds.',
+    '4. Never run crontab, never read /etc/cron*, and never say there are no tasks until cron_list has returned.',
   ].join('\n')
 }
 
diff --git a/package.json b/package.json
index f696f7a..0d02a93 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "dsh-ops-cron",
   "description": "Scheduled tasks for DeepSeek Harness: Agent cron_* tools + sidebar 定时任务, with DSH or WhatsApp/IM delivery per job.",
-  "version": "0.1.12",
+  "version": "0.1.13",
   "private": false,
   "type": "module",
   "repository": {
diff --git a/test/tools.test.js b/test/tools.test.js
index f67473e..bb6bbad 100644
--- a/test/tools.test.js
+++ b/test/tools.test.js
@@ -435,3 +435,25 @@ test('registerCronTools registers each definition and disposer unregisters', ()
   off()
   assert.deepEqual(registered, [])
 })
+
+test('cron tool output schemas never use type arrays (Host rejects them)', () => {
+  const defs = cronToolDefinitions({
+    async createJob() { return {} },
+    async listJobs() { return [] },
+    async pauseJob() { return {} },
+    async resumeJob() { return {} },
+    async deleteJob() { return {} },
+  })
+  const bad = []
+  function walk(node, path) {
+    if (!node || typeof node !== 'object') return
+    if (Array.isArray(node.type)) bad.push(`${path}.type=${JSON.stringify(node.type)}`)
+    if (Array.isArray(node.oneOf)) node.oneOf.forEach((branch, i) => walk(branch, `${path}.oneOf[${i}]`))
+    if (node.properties && typeof node.properties === 'object') {
+      for (const [key, child] of Object.entries(node.properties)) walk(child, `${path}.properties.${key}`)
+    }
+    if (node.items) walk(node.items, `${path}.items`)
+  }
+  for (const def of defs) walk(def.output?.schema, def.name)
+  assert.deepEqual(bad, [])
+})