Identity is defined by RFC 8621 under urn:ietf:params:jmap:submission, not
under mail. ihasmail asked for mail alone, so Stalwart 0.16 rejected both
Identity/get and Identity/set with unknownMethod: no identities were ever
listed, none could be created, and sending then failed with "No sending
identity available". Older Stalwart builds accepted the calls anyway, which
is why this went unnoticed.
Also filter `using` down to the capabilities the session actually advertises.
A server must reject the entire request with unknownCapability when `using`
names something it does not implement, so one over-eager urn would take down
every call sharing the batch — including, on a server predating the submission
capability, the mailbox and message loads batched alongside an identity fetch.
Fixes#12
"Send failed: Invalid property or value." is Stalwart's description for
invalidProperties, and on its own it says nothing about what to fix. The
SetError also carries a `properties` array naming the offending fields, which
every call site was discarding.
setErrorMessage appends them, and the 35 places that surfaced a SetError -
send, save draft, mailboxes, calendars, contacts, sieve, files, signature
images, sharing - now go through it.