This exists, T57370: [Epic] VisualEditor: Implement some form of auto-save to help with browser crash recovery and accidental tab closing
but it isn't mentioned anywhere in mw:Extension:VisualEditor, so technical users of the extension (3rd party developers and admins, new Wikimedia staff, etc) have no hints as to how it works.
See also: T202076: Document the VE auto-save feature for end-users