interoperability of workspaces and bookmark folders

[cognominal]

At any given time, one wants to deal with a limited number of workspaces out of many more.

This can be done by associating a workspace with a underlying eponymous bookmark folder. Say, under a dedicated bookmark folder named "workspaces".
Such bookmark folder associated to a workspace would contain the pinned tabs as entries.
For simplicity the folders in the workspace folder could not contain subfolders. Or if they do, the logic of tabs handling must handle it.

The bookmark menu should have a "workspace" sub menu. A entry with a x in that menu means an open workspace. Selecting an entry in that menu will toggle the status closed/open of that workspace.
The context menu of a workspace should have a "close workspace" entry.
One could drag a regular bookmark folder into the workspace one. The reverse operation should be supported.