[Feature request] Command prefix and/or unit control for forked apps

[Vladimir-csp]

Is your feature request related to a problem? Please describe.

In a modern systemd-managed user session apps are being put into user's scopes or services. Apps spawned (when opening files in them) by PcmanFM remain a part of PcmanFM's scope or service.

Describe the solution you'd like

Two non-conflicting solutions:

• Command prefix for apps that are being spawned. A wrapper can handle session stuff for apps that are spawned.
  • a simple wrapper can take command line prepared by PcmanFM as is.
  • a desktop entry-aware wrapper can take the deskop entry path and file argument(s) by itself and process them.
• Direct unit control by PcmanFM.
  • option to choose parent slice (default: app.slice)
  • option to choose scope or service unit type (default: PcmanFM's own unit type)
  • naming and metadata options (how to generate unit IDs beyond recommended app-${DE}-${name}@${random}.service or app-${DE}-${name}-${random}.scope, how to translate desktop entry ID and attributes like Name, Comment to unit attributes like ID and Description).

Describe eventual alternatives you've considered

Context

I worked on app unit handling in uwsm app wrapper of my session manager extensively, feel free to query results of this experience for tips, tricks and caveats.