Who sees the button
The runtime asks Fluid whether the current page can be shared by the current visitor, and shows the button only when the answer is yes.
Guests trigger no request at all, because the runtime skips the check when the session marker cookie is absent.
What can be shared
The current page URL identifies what is being shared. Supported resources are products, media, pages, and playlists. The share is always credited to the member who is signed in. It is never credited to an identity taken from the URL, so a member browsing another member’s link still shares as themselves.Performance
The button itself is tiny. The share dialog and its dependencies load only when a member opens it, so a page that is never shared never pays for the dialog.Styling
The button and dialog read the same--fluid-account-* custom properties as your other Fluid account surfaces, so an existing override applies here too: