What
Fix the "missing essential plugin org.jetbrains.android" error after an Android Studio upgrade.
Why
Upgrades sometimes write plugin names to disabled_plugins.txt even though they're required for Android development. Deleting that file lets Android Studio re-enable the bundled Android plugin on next launch.
How
cd ~/Library/Application\ Support/AndroidStudio*.*
rm disabled_plugins.txt
Restart Android Studio. Adjust version number in path as needed.