The Share popover is one flow: Online (the file is published to the server in
Preferences and the server names its links with short codes) or Local network
(the app hosts; the code carries its address and the session's secret), one
Start sharing button, the code large with Copy code and Copy link, who is here,
can edit / can view, and Stop sharing. Join with a code is one field in the
popover, on the home screen and in the Join dialog, for a code of either kind
or an invite link.
Protocol (within version 2, new variants last): Resolve / Resolved and Admin
code. The server keeps a stretched hash and the wrapped token, never the code,
and limits wrong codes per address (with a lockout) and for everyone. Older
servers leave the links in place of a code; older apps join by link.
collab.share, collab.join {code}, code and share in collab.peers; the server
preference defaults to the built-in server and can be reset or turned off.
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