Sessions support or save BSP layout

Looks like there is no way to save all windows positions/dimensions in BSP mode? It would be really useful to support it. Something like a session file with saving all windows state to it and then use it later to recover. For example after Reboot system restarts all opened applications and desktop became a mess with BSP layout enabled. If we save windows state before reboot, we could recover them easily.

Session like behaviour would also be useful to add a "mode" with various windows preinstalled in fixed positions. For example, I setup windows to positions suitable for some task and then recover that position using single shortcut. I know about workspaces, but their state also lost after reboot.

Third scenario is creating Cmd + Z like button. Say you made a mistake in shortcut and want to revert it, but most of actions is not easy to revert (except toggles). That case you may also save state in shortcut handler before executing main action and then use it to revert action.

What do you think about it?

No files, tests, or entry points are identified. First clarify whether the goal is persistent BSP layouts, reusable window-position modes, action undo, or some combination; define the session format, supported state, recovery behavior, and acceptance tests before locating implementation points.

Written by the indexing model from the issue text.