• user is in web UI
• finds a file and wants to open it locally (e.g. Collabora is not sufficient, Inkscape for SVG, etc.)
• user clicks "edit locally"
• special link type (tbd: nc://open/$account@Server/$remotePath)

On Desktop:

• client listens to this link
• client opens file if already synced, if not syncs it first, then opens it via native file handling mechanism)
• if account not set up or file not syncable (e.g. folder is excluded by "selective sync") show an understandable error message
• file is being locked while editing this file