## What changed
- Add `subErrorType` to external agent config import failures and carry it through progress and completion notifications, persisted import histories, and analytics.
- Expose plugin store failure subtypes from `PluginInstallError` so manual installs and imported plugins report details such as `failed_to_copy_plugin_file` while failures without a subtype remain `null`.
- Keep existing persisted import records compatible by defaulting the new field when it is absent.
## Testing
- Cover store I/O subtype extraction, analytics serialization, persisted import histories, and migration notification fixtures.
GitOrigin-RevId: ec1a85623fc826cbd7cfe9f55c2dd2bc86665937