diff --git a/package.json b/package.json
index 2405ef3..52abebe 100644
--- a/package.json
+++ b/package.json
@@ -51,11 +51,11 @@
     "src"
   ],
   "scripts": {
-    "build": "rm -rf lib && tsc -p tsconfig.build.json && tsdown",
+    "build": "rm -rf lib && tsc -p tsconfig.build.json && tsdown && node scripts/apply-ime-guard.mjs",
     "typecheck": "tsc --noEmit",
-    "bundle": "tsdown",
+    "bundle": "tsdown && node scripts/apply-ime-guard.mjs",
     "watch": "tsdown --watch",
-    "prepare": "tsdown",
+    "prepare": "tsdown && node scripts/apply-ime-guard.mjs",
     "test": "vitest run"
   },
   "license": "MIT",
diff --git a/scripts/apply-ime-guard.mjs b/scripts/apply-ime-guard.mjs
new file mode 100644
index 0000000..97c6c1a
--- /dev/null
+++ b/scripts/apply-ime-guard.mjs
@@ -0,0 +1,26 @@
+// 持久 IME 守卫补丁（2026-08-10，changelog 见 AGENTS.md）：
+// Univer InputNumber 在 document capture 拦截全页 ↑/↓ 且无 isComposing 守卫，
+// 会摧毁中文输入法组合（候选词导航被劫持）。每次 build 后自动重打。
+import { readFileSync, writeFileSync } from 'node:fs'
+import { fileURLToPath } from 'node:url'
+import { dirname, join } from 'node:path'
+
+const root = join(dirname(fileURLToPath(import.meta.url)), '..')
+const target = join(root, 'lib/client.js')
+const src = readFileSync(target, 'utf8')
+
+const pattern = /function handleKeyDown\(e\) \{(\s*)if \(disabled\) return;/
+const guard = 'function handleKeyDown(e) {\n\t\t\t\t\tif (e.isComposing || e.keyCode === 229) return;\n\t\t\t\t\tif (disabled) return;'
+
+if (src.includes('e.isComposing || e.keyCode === 229')) {
+  console.log('[apply-ime-guard] guard already present, skip')
+  process.exit(0)
+}
+const count = src.match(new RegExp(pattern.source, 'g'))?.length ?? 0
+if (count === 0) {
+  console.error('[apply-ime-guard] ERROR: pattern not found in lib/client.js — univer structure may have changed, inspect manually!')
+  process.exit(1)
+}
+const next = src.replace(pattern, guard)
+writeFileSync(target, next)
+console.log(`[apply-ime-guard] injected IME guard (${count} site(s))`)