"Allow apps to find accounts" has no effect on accounts added before it was enabled

The "Allow apps to find accounts" toggle (Legacy Settings, key auth_manager_visible) only takes effect for accounts added after it was switched on. Turning it on later does nothing to accounts that already exist, and nothing in the UI says so. This affects any app that enumerates accounts with getAccountsByType() rather than going straight to getAuthToken() — Viber and WhatsApp are the ones people keep reporting, but it is not app-specific.

The visibility row lives in /data/system_de/0/accounts_de.db, table visibility, as android:accounts:key_legacy_not_visible. Without it an app that holds neither GET_ACCOUNTS_PRIVILEGED nor the authenticator signature gets an empty list back. In the current tree setAccountVisibility is written in exactly one place, LoginActivity.java (lines 186 and 441), guarded by isAuthVisible:

if (isAuthVisible(this) && SDK_INT >= 26) {
    accountManager.setAccountVisibility(account, PACKAGE_NAME_KEY_LEGACY_NOT_VISIBLE,
                                        VISIBILITY_USER_MANAGED_VISIBLE);
}

The toggle itself is handled in AccountsFragment.onCreatePreferences, where the listener persists the value and refreshes the UI, with follow-up actions for two other settings:

SettingsContract.setSettings(requireContext(), Auth.getContentUri(requireContext())) { put(preference.key, newValue) }
updateSettings()
if (preference.key == Auth.TWO_STEP_VERIFICATION && newValue) registerGcmInGms()
if (preference.key == Auth.FIND_DEVICES && newValue) registerGcmInGms()

Auth.VISIBLE has no such branch, so enabling it never reaches setAccountVisibility. I confirmed that on device by toggling it off and on and re-reading the table: no write happened.

To reproduce, add a Google account through microG with the toggle off, then enable the toggle, then open any app that lists accounts — WhatsApp chat backup or Viber backup will still show no account. Reading the table shows the missing row:

adb shell "sqlite3 /data/system_de/0/accounts_de.db \
  \"SELECT _package, value FROM visibility WHERE _package LIKE 'android:%';\""

This is the mechanism behind the workaround people have been passing around in #1988 since 2024 — enable the toggle, then remove the Google account and add it back. That works because re-adding is the only moment the row gets written. It has been independently confirmed there by several users on CalyxOS and /e/OS, and the same root cause fits #2398 and #2244.

A fix would be to apply the setting when it is switched on, in the same place the other two settings get their follow-up: iterate the existing com.google accounts and call setAccountVisibility(account, PACKAGE_NAME_KEY_LEGACY_NOT_VISIBLE, VISIBILITY_USER_MANAGED_VISIBLE). Clearing it again when the toggle is switched off would keep the two directions symmetric.

Tested on LineageOS 23.2 for microG (Android 16), microG GmsCore 0.3.16.252432, on a Redmi Note 10 Pro. The code references above are from current master.