ここ作者みてますか?
archon版にこれお願いします。
manifest.json
--- manifest.json 2015-02-24 15:00:46.000000000 +0900
+++ jp.co.airfront.android.a2chMate.android/manifest.json 2015-03-02 10:38:19.444771245 +0900
@@ -10,7 +10,7 @@
     "apkList": [
       "custom-android-release-1400197.apk"
     ],
-    "enableExternalDirectory": false,
+    "enableExternalDirectory": true,
     "formFactor": "tablet",
     "name": "jp.co.airfront.android.a2chMate",
     "orientation": "landscape",
@@ -54,7 +54,9 @@
     "clipboardRead",
     {
       "fileSystem": [
-        "write"
+        "write",
+        "retainEntries",
+        "directory"
       ]
     },
     "
https://clients2.google.com/",