Switching to an account somebody shared pointed the whole app at it. The
rule was "use the selected account if it can do this", and a shared file
account can, by definition, do files.
ihasmail keeps its settings in the account's Files -- that is what makes
them follow you between devices -- so changing any setting while looking
at somebody's shared folder wrote `settings.json` into *their* storage,
creating the `ihasmail` folder there to do it. Signature images went the
same way, and push registration would have gone to whichever account was
on screen. Reading someone else's data by mistake is bad; writing yours
into theirs is worse, and one line was doing both.
There are two questions, and they had one answer:
- what am I looking at -- follows the switcher, because switching to a
shared account is how you read what was shared
- what is mine -- never does
So `accountFor` keeps the first meaning and `ownAccountFor` is the
second, used by settings sync, signature images and push. A `??
accountId` fallback in `loadStoredSignature` went with it: the reader's
own signature, reached through whoever happened to be selected.
A third rule was hiding in the first. A capability the selected account
does not advertise fell back to the selected account anyway, so a session
naming no primary for something aimed it at whoever was selected --
somebody else. It now answers with nothing, which is honest: the feature
is unavailable, rather than pointed at a stranger.
What this does not settle is whether the mail, calendar and contacts the
switcher appeared to offer were ever really reachable, or only asked for
and refused. That depends on what Stalwart advertises on a shared
account, which needs a look at a sharee's session; if it advertises
capabilities nobody shared, more is needed here than routing.
