Error: Unable to Write File to applicationDirectory in Capacitor Filesystem

Problem: writeFile fails on applicationDirectory

When attempting to write a file to applicationDirectory using Capacitor’s Filesystem plugin, the operation throws a failure. The directory is intended to contain the app bundle’s assets and is read‑only after the app is installed on both iOS and Android.

Constraints & Considerations

• applicationDirectory is immutable post‑install; attempts to write return an error.
• Mutable storage must be placed in documentsDirectory, libraryDirectory, or cacheDirectory.
• Data in documentsDirectory is backed up to iCloud or device backups unless excluded.
• Path strings differ between iOS and Android and can change across OS updates.

Unresolved Questions

1. What is the precise error message returned when writing to applicationDirectory on iOS vs. Android?
2. Which directory constant should be used for data that must persist across app launches but should not be exposed in backups?
3. How can developers explicitly prevent sensitive files from being included in iCloud or device backups on iOS?