v7.0.0

• Breaking: 1:1 content can carry the profile key, with
  hosted.profileKeys. Give createHostedSignalProtocolClient a
  HostedRelayProfileKeys object: a getOwnProfileKey() function and a
  contacts store. Each 1:1 DataMessage then carries the account's profile
  key in the Signal DataMessage.profileKey field, inside the encrypted
  content. Before a 1:1 string or byte send to a contact that does not have
  the current key, the SDK sends one PROFILE_KEY_UPDATE DataMessage (flag
  4). The receiving SDK keeps the key with storeReceivedProfileKey, derives
  the contact's presence key, and calls grant(). It gives a key update to no
  application hook. The SDK calls accessKey() when the socket connects and
  when the profile key changes, so a rotation revokes the old presence key and
  the next message delivers the new one. The app writes no key code. No key
  goes in a field that the Relay can read: the profile key goes only in
  encrypted content, and the presence key goes only in the presence-key and
  presence-read frames. Group messages do not carry the key. Each device of
  an account must return the same profile key. A 6.0.x receiver does not know
  the key update and gives it to onMessageDecrypted. Update all clients to
  7.0.0 before you set hosted.profileKeys.

• New: hosted presence with hostedRelayPresence(client). It has
  policy(), setting(), setVisibility(), read(), and watch(). Each
  request is one versioned frame on the mailbox socket. Its answer comes back
  on the same socket. One read frame carries at most 100 accounts, and
  read() splits a longer list. A null result hides why the account has no
  presence.

• New: HostedRelayPresenceError. Its code is the Signal Protocol
  Relay's own code, for example PRESENCE_SETTING_FORCED or QUOTA_EXCEEDED.
  The SDK adds the codes NOT_CONNECTED, BUSY, TIMEOUT, and
  FRAME_REJECTED too. With code 1008, a Signal Protocol Relay without
  presence frames closes the socket. Each pending request then fails with
  FRAME_REJECTED, and the subscription reconnects.

• New: watch() polls every 30 s in the foreground. It reads when the
  socket connects and then every 30 s. It calls the listener only on a change.
  The poll stops while the socket is down. With bindRelayLifecycle, the
  socket closes in the background, so the poll stops there too. On web, a
  hidden tab continues to poll.

• No heartbeat. The SDK sends no presence heartbeat and reports no
  presence state. The Signal Protocol Relay records the socket edges.

• New: the presence key, with accessKey() and grant().
  accessKey(profileKey) derives a 16-byte key from the 32-byte profile key.
  It uses HKDF-SHA-256 with an empty salt and the info
  open-e2ee-presence-key-v1. It registers the key and returns it as 22
  base64url characters. A new key revokes the old one.
  grant(account, presenceKey) keeps a contact's key for read().

• New: hostedRelayWakePresence(client) for a client with no socket. A
  wake client has no mailbox subscription. It runs in a push handler or a
  background task. Its presence has the same members without watch(). Each
  request is one authenticated POST /v1/signal/presence. Neither carrier
  falls back to the other.