T9: Screensaver and suspend sync — StateMessage via D-Bus #15

Parent

#6

What to build

Keep the control surface in sync with desktop lock/suspend state. The daemon subscribes to two D-Bus signals and pushes StateMessage to all connected clients.

• org.gnome.ScreenSaver.ActiveChanged(bool) on the session bus → push StateMessage(locked=True) on lock, StateMessage(locked=False) + current LayoutMessage on unlock.
• org.freedesktop.login1.Manager.PrepareForSleep(bool) on the system bus → same locked/unlocked sequence on suspend/wake.

The client already has a StateMessage type; it should render a "desktop locked" overlay when locked=True and suppress input.

Acceptance criteria

• Activating the GNOME screensaver causes the client to show a locked state
• Deactivating the screensaver restores the client to the current layout
• System suspend blanks the client; wake restores it
• StateMessage(locked=True/False) is the only new protocol message; client suppresses widget input while locked
• Test: simulate the D-Bus signal via the fake backend; assert StateMessage is pushed with correct value

Blocked by

• T4: Per-app layout switching — focus watcher → layout push #10 (per-app layout switching — layout push on unlock depends on layout state)