How to handle a download the host determines (via DownloadResult.version_history) is a NEWER revision of an already-catalogued archive.

Declaring this is entirely optional even for a plugin that does populate version_history: the host detects version_history support by static analysis of the plugin's own source (a plugin_introspect dispatcher call), so the settings UI offers both policies to the user regardless, falling back to DEFAULT_RELATIVE_NEWER_POLICY when the plugin states no preference. Declare it only to express a different default than that.