Found a direct UI hit at least with some resource strings in the last/mainline branch that checks out from the repo by default which is cm-14.1. It started by finding a repository that happened to have the words settings and application in its name was a very strong clue to start with. In the screenshot above you can see that the UI reads Root access and that is what we find verbatim in this resource file.
<!-- Setting checkbox title for root access -->
<string name="root_access">Root access</string>
<string name="root_access_warning_title">Allow root access?</string>
<string name="root_access_warning_message">Allowing apps to request root access is very dangerous and could compromise the security of your system!</string>
<string name="root_access_none">Disabled</string>
<string name="root_access_apps">Apps only</string>
<string name="root_access_adb">ADB only</string>
<string name="root_access_all">Apps and ADB</string>
Running a blame on that block of text lead to this diff
Going back to the branch that is installed on the device, or at least the closest stable matching variant, I do in fact find that root access resource string being present. I'm hoping there's something interfering that I can twiddle to bring that option to the forefront again because it's not showing up.
Doing a blame on that version leads to this commit...
- Root over ADB is now disabled by default on non-eng builds
- Requires support in su binary and adbd
- Root access can be configured to use ADB only, apps only, or all https://github.com/CyanogenMod/android_packages_apps_Settings/commit/c39be56248000ac1c88909874b28a80f5370fb2a