Finally fixed this!
After compiling the forked budgie-screensaver and getting the same behavior, realizing the problem is on the receiving side of that signal (which I had no idea which application would be to follow through on that) I broke my desperation threshold: I reinstalled Solus (home is in a separate partition) yet the problem still persisted!
Gutting as this was, I obviously knew at this point that it's something in my configuration (so .config folder). I made a backup of that config folder (and a mental note to myself to add the step of creating a new user and testing with that before reinstalling the OS) and then proceeded to rename it and log in again: BOOM screensaver works but a ton of customization missing!
So now I was trying to find what exactly in .config affects this. I restored and renamed subdirs and very quickly narrowed this down to the "dconf" folder.
I learned that this file can be dumped to text mode and ran dconf dump / > dconf.txt
and reviewed it. I located 3 keys related to power management settings:
[org/gnome/desktop/screensaver]
color-shading-type='solid'
idle-activation-enabled=false
lock-delay=uint32 30
lock-enabled=true
picture-options='zoom'
picture-uri='file:///usr/share/backgrounds/solus/SolusFresh.png'
primary-color='#000000'
secondary-color='#000000'
[org/gnome/desktop/session]
idle-delay=uint32 60
[org/gnome/settings-daemon/plugins/power]
idle-dim=true
power-button-action='interactive'
sleep-inactive-ac-timeout=3600
sleep-inactive-ac-type='nothing'
sleep-inactive-battery-timeout=1800
sleep-inactive-battery-type='nothing'
The only thing suspect was idle-activation-enabled
but nothing I did in the setting gui would flip it. Also, the above gsettings reset org.gnome.desktop.lockdown disable-lock-screen
had not helped in my case (tried it again anyway). I ended up changing it manually with dconf write /org/gnome/desktop/screensaver/idle-activation-enabled true
which worked, but that did not help either (no screensaver).
So I just went nuclear again: logged out from X and logged into console, killed the dbus daemon process so that it is not running and reset all 3 categories with:
dconf reset -f /org/gnome/settings-daemon/plugins/power/
dconf reset -f /org/gnome/desktop/session/
dconf reset -f /org/gnome/desktop/screensaver/
A fresh dump revealed that these were no longer present in the file.
So, I logged back in, went to "Settings->Power->Blank Screen" turned it down from 5 to 1, waited a minute and ...BOOM !!! Screensaver on! Screen blank. Power saving starts! On moving mouse the system is locked and asking for the password...
I wasted probably 10 hours on this and do not wish it on my worst enemy.
The only positive is that I've learned a bit about gnome's architecture, read some gnome code, built the screensaver manually, etc... So at least I learned something...