Stalwart 1.0 advertises `urn:ietf:params:jmap:metadata` by default, but
its handlers are still `todo!()`: a get that selects `metadata` or
`privateMetadata`, a /changes call with `ignoreMetadataOnlyChanges`, or
an Email/query filter such as `metadataExists` panics the request on the
server.
- Mailbox/get and SieveScript/get ask for explicit RFC property lists
(the same as today's 0.16 and 1.0 defaults) instead of none, so a
later default that includes metadata cannot reach them.
- Plugin category tabs (`tabs.set`) reject JMAP Metadata filter
conditions at any depth; the tab query went to Email/query verbatim.
- A test checks the requests the client builds, and the request-building
sources, for metadata properties, the /changes argument and the
capability.
